Cooling the 1KZ-TE in the Hiace Super Custom

The Hiace 3.0TD has the 1KZ-TE engine that in hot climates has a reputation of overheating and cracking the head, so avoiding this is quite a good aim.

This forum covers the subject in the Hilux in supreme detail:

https://www.landcruiserclub.net/community/threads/cooling-the-1kz-te-motor.130304/
https://www.landcruiserclub.net/community/threads/cooling-the-1kz-te-motor.130304/page-8#post-1240706

Please see post #2 in this thread for my experiments in this area.

Moved from the cruise control thread:

Post 1
I read this about a top-hose thermostat conversion, sounds good, completely eliminates temperature spikes and gives a rock steady gauge:

https://www.landcruiserclub.net/community/threads/cooling-the-1kz-te-motor.130304/page-8#post-1240706

The top hose fits a 40mm pipe so the MG-ZT 38mm housing should fit fine as long as it's not too long as the top-hose still needs to be flexible for engine movement - so maybe the internal one ( https://www.ebay.co.uk/itm/Rover-75-MG-ZT-Diesel-CDTi-Inline-Thermostat-Kit-With-Instructions-86-Degrees/222986856020 ) if it fits.
The existing thermostat is however buried just behind the alternator so access is very poor so that looks like an Odyssey. I'd leave the lower thermostat frame in place to restrict the flow from the head (flow from the head is diverted to the sensor of the thermostat to make it open when the head gets hot, which it eventually does) but cut out the restriction part of it.

Page 2,3 of this gives the photos, basically the water enters the head at the back and exits at the front, going down to the buried thermostat bulb on the RHS and out to the temperature sensors and top-hose to the LHS where the cap is. So the old thermostat would need to be left open to restrict that flow back to the pump as it it was still there, but cut open so all temperature regulation was done via the new top-hose thermostat, which as a bonus would be far easier to change every few years...

Post 2
Some data on the temperature gauge 'damping':

Had a measure of the sender unit for the gauge in the Hiace, just to see how the dial reacted to various resistances. Note that this is the horizontal sensor/sender that goes right into the head with the yellow wire on it. At room temperature this sits at 1133 Ohms and the engine is cold. I then disconnected the wire so I could use various resistors in place of the sender to see how the gauge responded.

BTW the vertical sensor below the radiator cap with the purple wire controls the electric fan on Rad II which comes off if disconnected, so this has a thermo-switch action.

Data
At 255 Ohms the dial just comes alive and indicates on the bottom bar

Then adjusting down to 100 Ohms the gauge rises smoothly until it's at the bottom of the thermometer bulb symbol, about 45% of the way up. This is a lovely calming position because everything is under control and the van is doing well.

Adjusting all the way down to 39 Ohms has absolutely no effect, still the lovely calming 45% position. This is the damped or 'dead' zone of the gauge.

Then lowering down to 23.5 Ohm the needle suddenly pops up.
Note I only had fixed resistances at this point so it may move slightly earlier, somewhere between 39Ohm and 23.5 Ohm it makes it's lunge upwards. 23.5 Ohms is now telling the user 80%: getting a bit warm, careful now.

Then at 19.5 Ohm (the next fixed value I had available) it clearly says 'Hot' just a fraction below the top bar.

Conclusion
The Hiace SC temperature gauge is heavily damped to prevent the driver from seeing anything from 'warmed up' (100 Ohms) to 'Oh dear it's a bit hot now' (23.5 Ohm). Next stop is 'Hot!!!!' at just 19.5 Ohm.

It seems to me that if the gauge can be tuned to show the following in a linear manner:

255 Ohm = A bit cold
100 Ohm = Just right
20  Ohm = Hot!!!!

then it would be considerably more useful.
ETA: See this thread on how to modify it with a 220 and 47 ohm resistor:
https://hiace-super-custom.forumotion.com/t3426-modding-the-toyota-temperature-gauge-no-zener-dead-zone

I also looked into the thermostat design Toyota have used:


That bit at the end/bottom is a pressure relief valve, so when the thermostat is closed the hot water trying to leave the head forces it open and in doing do warms the area up a bit until it finally decides to open. So some of its action is from the temperature in that area (there's an oil cooler in there) and some from the head, so it's not really responding to head temperature at all but to an average temperature of block, oil cooler and a delayed head temperature as the head inlet basically has to heat up enough flowing water to wake the thermostat up, a bit like a kettle's off switch - the element can get hot if it likes but nothings happening until the water is hot.

I also suspect when the thermostat gets a bit old the main valve gets a bit sticky, and when it gets stuck the mildness + delay of the action to open it means the head roasts before it opens - hence you get the temperature spikes and related head gasket issues. So if using this arrangement I think installing a proper temperature gauge (or fixing the instrument panel one) is a very smart idea, then if it starts to get to hot just pull over and see if it cools down while you are at idle for a few minutes.

With a brief spurt of power I can't see any reason why that thermostat should open in time to save the head.

This relief valve also needs to be there when converting to a top-hose thermostat arrangement so IMO this thermostat should never be fully removed as that would allow water from the head to re-circulate too easily, we really want it be pushed out to the radiator to be cooled before we get it back. Then when the radiator itself warms up this warms up the viscous coupling to cool the radiator.

Looking at the access to the side mounted thermostat I'm not sure I'm brave enough to do the conversion right now, maybe it's a job for the winter..


Interestingly all Hiace 1KZ-TE thermostats appear to be 76 C ones, so it looks like Toyota knew there was an issue and didn't use the 82C one. This also means lower MPG of course. An outlet thermostat would be 89 C as it could respond rapidly and give more MPG.

Maybe I'll just buy that thermostat first and see how easy it looks to modify.

Maybe it is also worth looking into an intercooler setup?
That significantly makes the head run cooler.

Next to that, or in combination, you could use an EGT gauge, which also gives you an indication.

You could also add a digital temp gauge which you mount on the head.

An intercooler is an excellent suggestion although space is very tight there, just enough for a catch can.

The issue with all engine designs with inlet thermostats appears to be one of rapid thermal changes (shock) rather than absolute temperatures. BMW seems to get away with it but they may have just designed an engine with a very even cooling/heating character so it gets away with it.
MG, Toyota, Landrover and Porsche however all suffer from the inevitable effect of using an inlet thermostat, which I'm guessing must have seemed like a great trendy thing to do in the mid-90's - I assume there is a paper out there that drove previously sensible engineers to do this insane thing.

If there was a paper, it was probably based on a theoretical thermostat with no lag. In the real world however it takes time for the wax to melt through, and more time for the wax to solidify again simply due to the limited thermal conductivity of wax, despite it being in a nice copper tube. Add to that the fact it is balanced between cold inlet water and hot head water and it has significantly more lag.

So the thousands of damaged Porsche 996/997, Toyota 1kZ and MGF engines are simply down to this schoolboy error of trying to be 'smart' and using an inlet thermostat. The problem is one of violently oscillating temperatures it causes - driven like in all good oscillators - by a delay - in this case the delay of the wax thermostat and water mixing.
The inlet thermostat has a head channel of hot coolant (a bypass) directed at the back of the wax bulb, the rest of the bulb is in the gallery of coolant - in the 1kZ case just above the oil cooler.

The oscillator:
Loop start:
When the head heat wins the balance the thermostat opens and lets in some cold water. In winter this is very cold which is why most MGF head gaskets fail in the winter. This cold water floods into the head until the inlet thermostat - now swimming in cold water, closes up again. Then the head heats up nice and hot again and its bypass channel takes priority of the thermostat again and we goto 'Loop start' to give the head yet another violent thermal shock, and this happens again and again and again and again until the coolant system is warm.

Each time we use the engine.

Another sad side effect of the inlet thermostat is that a sudden burst of heat is again subject to quite a bit delay because the water around the thermostat has to warm up again before the outside of the thermostat bulb even knows about the heat. This causes a big heat spike that gives the head another big thermal shock, with in winter some impressive after shocks as again the system oscillates..

In the MGF these thermals shocks destroy head gaskets, loosen cylinder liners and play havoc with the insides, in Porsches the bores overheat and get scored, sometimes bits of cylinder falls off the open deck cylinders and of course the odd head gasket fails, in the 1kZ the head gasket fails and generally the head cracks too.

This interesting research has a graph of the violent oscillations that the inlet thermostat causes:
http://www.mgf.ultimatemg.com/group2/common_problems/HGF_pages/dave_monks/mgf_head_gasket_failure.htm

There is only one real fix for this in my view: getting rid of the oscillators active element: The inlet thermometer. Once warmed up of course an intercooler would be a huge help, that maybe a winter project one day

A pros and cons view of the 1kZ and possible fixes:

Inlet thermostat only
Con: Thermostat oscillates on each warmup, stressing head
Con: Thermostat closes when engine is switched off stopping convection: bad heat soak!
Con: Slow reaction can cause any sudden load to thermally stress the head

Top-hose thermostat , inlet thermostat jammed open
Pro: Thermostat in the right place to react
Con: Away from flow - will it react?
Con: Thermal shock when it opens
Con: Possible cavitation (destroys water pump vanes) if both bypass and top 'stat is closed


Top-hose thermostat, inlet thermostat removed
Pro: Thermostat in the right place to react
Pro: Allows good mixing of cold inlet + head bypass
Con: Away from flow - will it react?
Con: Thermal shock when it opens
Con: Head bypass also flows when hot

Top-hose thermostat with 2-4mm hole, inlet thermostat removed
Pro: Thermostat in the right place to react
Pro: Allows good mixing of cold inlet + head bypass
Pro: In moving stream from head - should react well
Pro: Slowly warms radiators avoiding thermal shock when it opens
Con: Head bypass also flows when hot
Con: Slower warmup

So the only solution that looks good to me is the last one, it's also quite simple which is nice.

Well I saw that somebody fitted an air to water intercooler eith the 1kz in a hiace, very tight fit. So that means an additional advantage as it delays the heat build up a bit. That is just because of the water taking up
/ buffering the heat and still giving cool air for some short time.

I found something. But he modified the rear acces panel:
http://www.offroadexpress.kiwi/Forums/viewtopic.php?t=34013

Interesting links, I'll have a read of them, a watercooled version would indeed be fine if hooked into the right point.

BTW I decided to remove my thermostat to have a look at how easy it was and think about what to do, the van hasn't had any bad symptoms but with a trip coming up I thought it was easier to check in the garage then by the side of the road LOL.



It's worth bearing in mind that from the factory in normal usage for most people there really isn't a problem, but radiators silt up, coolant ages, leaks happen and thermostats die, a good first move would be to modify the temperature gauge so you can see what the engine is actually doing:
https://hiace-super-custom.forumotion.com/t3426-modding-the-toyota-temperature-gauge-no-zener-dead-zone

..and then perhaps make sure the coolant is good and check the 'stat anyway as it's super-vital on the 1Kz. In fact I tested my 76C stock thermostat I took out, at around 85 C it just about opened and then at 100C it fully opened, and stayed open - so it's faulty anyway, just as well I dug it out LOL.

Instructions on removing the Hiace 1KZ thermostat;
The bottom radiator hose runs into a cast hose/thermostat housing behind the alternator with 3 x M6 bolts with 10mm heads on them. There are also a couple of pipes on a bracket that bolts onto this cast hose so you need to undo that first.

Access is tight but not too bad in practice. First drain the water from the tap on the front radiator into a clean washing up bowl and empty into a container for proper disposal. Also get a huge 500mm square tray perhaps from a garden centre to put under the engine toward the side you are working on to catch coolant. Keep coolant way from cats as they will rapidly die from kidney failure if they lick it.

You'll also need to remove the drivers seat (slide+tilt forward to access the electrical plug first) and the panel below it. Now is also a good time to contemplate fitting that catch can kit too but that's another topic.  

Then undo the heater hose pipe sticking out of the top of the thermostat housing. It's not actually attached to the housing thankfully but looks like it is. Gentle with the pipe, wiggle, twist etc and it will ease off without breaking anything. The key is to improve the Hiace, not to give yourself difficult jobs fixing broken stuff on a stranded van..

Your job now is to identify the top two M6 bolts top and bottom of the thermostat housing. You'll need a 6 point socket on an extension on a 3/8" handle. Don't use a 12 point socket because rounding off those bolts is harder than finding 6 side sockets.

** Then get a tiny peen hammer and give the bolt heads a whack so the hammer rings, and you can also spray some easing oil over the housing as technically the bolts are outside of the rubber gasket so the oil may/should find them.

Then use the sockets to gently try the bolts. Keep a gentle even constant pressure and wait. If/when it doesn't budge try again after a cup of tea by going back to **. Repeat as needed. I'm going to assume you get them undone successfully here. When you put them (or new ones) back in use copper-ease on the threads, make sure the threads are dry and don't tighten them to too hard as the rubber does the sealing, not the teeny bolts, their only job is to press the thermostat valve against the head bypass inlet and to support the cast pipe/housing.

Disassembly
Once the top two bolts are turning the main task is complete. Now undo the bracket bolt on the cast pipe. Then undo the lower M6 bolt (should be easy as it's in a dry location), then undo the top two M6 bolts.

Gently ease the cast pipe away from the block, the thermostat will be stuck in the block. You can now carefuly push the housing toward the ground so the top level with the middle of the thermostat. Use a small screwdriver hooked over the end of the stat to wedge the thermostat out from the block. Take care where the tip goes and just apply constant pressure and time will do the rest.

Hiace4wd wrote:

I found something. But he modified the rear acces panel:
http://www.offroadexpress.kiwi/Forums/viewtopic.php?t=34013

Wow that guy can fabricate stuff well, amazing skills, way beyond mine LOL. Interesting about the inbalance of the manifold and the gas flowing, if I ever have the manifold off to clean out the inevitable EGR crud I'll think about having it flowed - or at least to grind any casting edges off.

Just an update to the 1kz-te cooling system research, it appears that fixing cooling systems is quite widespread!

The best solution I came across being the 'constant flow' one that landrover developed and uses. It involves a PRT - a Pressure Relief Thermostat that allows for odd situations to be managed.

The basic idea of this is to always maintain maximum flow around the engine which evens out head and engine temperatures at all times, so there is no 'shut-off' with the thermostat, it merely diverts the flow down a big bypass back to the engine when no cooling is required. Its action is like a thermostatic shower but the mixing is determined by the 'hot' side of the shower



The thermostat fits on the return side of the radiator which may raise some alarm bells, but it's fed directly from a wide bypass tube direct from the head so it's not slow to react at all. Also on the 1kz-te Hiace there is a parallel bleed tube in the top so a top-hose thermostat is not such a simple thing anyway.

So the fitment is this: The top-hose is Tee-d off with a wide bore hose that (on the Hiace) has to head straight down. Then it needs a 90 degree bend to the right under/behind the main pulley and a tilt to the front to hook into the thermostat bypass port,  which has it's other ports connected in the middle of the bottom hose a few inches away from the radiator. Exact placement is yet to be determined.

The PRT's single port is for the cool radiator outlet, the angled port is the always flowing one going back to the engine and the straight one of the pair is the bypass feed from the T in the top-hose.

The old thermostat is then replaced with an empty thermostat frame.

This means that during warmup the radiator's exit is shut off but the bypass means the head coolant is flowing both out of the RHS to the open internal bypass and out of the top hose down the wide-bore external bypass. So a lovely even fast head flow for warm-up. And at all other times, no sudden swapping sides like the stock arrangement.

Then when warm the thermostat starts opening like a mixer shower, allowing some water from the cold radiator out, which then mixes with the bypass in the bottom hose to create a nice warm flow still.

Then when hot the bypass is fully closed (except for pressure events) and the radiator flows fully, but again unlike the original the head is still flowing both front exit ports: i.e. the old internal bypass (which would now be closed by the old thermostat) and the top-hose.

The mixing and pressure relief means that this system has a single gentle warmup and a more even cooling under all conditions, plus it never just runs either the top-hose or the internal bypass, both are always flowing so the pump is also happier and using less fuel.

The basic design is shown here (make sure to read right at the bottom for the actual system diagram)
http://web.tiscali.it/elise_s1/index.htm

The conversion of a Toyota Estima is here:
http://teoc.ws/community/topic/27315-little-project/

Apparently the PEL500110 grey landrover thermostat with the soft spring is the one to use.
More info as i collect it.

Thanks GPW looked on Ebay kit readily available at about £60 let us know when yours fitted and exactly what we need .

JT69 wrote:

Thanks GPW looked on Ebay kit readily available at about £60 let us know when yours fitted and exactly what we need .
 

Is there a kit already available for the Hiace? I found all the bits I think I need separately but I've not seen a kit except for landrovers, Elises, MGFs etc - have you a link?

I think with sedate driving in the UK and Japan the 1kz is probably fairly reliable, my old thermostat was also a 'reluctant to close again' so that probably evened things out too but the new scheme should make it far more robust in everyday driving.

The old system of hot coolant swapping between the exit hole on the RHS when the thermostat is closed to the hole on the LHS (to the top hose) when hot (and that flood of cold water coming in) could never have been a good idea though

The idea of a smooth uninterrupted flow through both all the time makes me want to change over all the more, I plan to drive this through heat baked Spain etc at some stage so the PRT mod is a must really.

Not a hiace kit just the Landrover one

Ah ok - I get you!!

The landrover 'stat is about £20 on it's own, 32mm pipe is about £25 (est as I have some already), the 38/32/38 Tee is about £20 and the silicone 45 degree is £8, the 90 degree swept bend £10 and about £12 of clips, so the total should be just under £100 which isn't bad. You may also need a new thermostat gasket (advised) when you gut the old inlet thermostat as new rubber seals much better than old rubber (as the old rubber retains impressions of the imperfections it found.

You also need 2 of these to fit the old hoses to the 32mm landrover thermostat: https://www.carbuildersolutions.com/uk/38-32mm-id-reducer

There seems to be two popular coolant sizes, 1.25" and 1.5" (32mm and 38mm), the Toyota uses 38mm and the land-rover uses 32mm so my design will use a 32mm bypass from the top hose that will go (via the swept 90 deg bend) into the silicone 45 deg and into the (centered outlet of the pair on the) thermostat (i.e. the bypass, the angled one is the mixed stream that returns to the engine). The lone port on it's own is to the return of the radiator.

That's my parts list in an ideal world anyway, I still have to see if this will work - it only looks like it all fits neatly so far, reality may be different! I'm hoping the curve of the bottom hose matches the curve of the thermostat's angles hose and the resultant angle plus the 45 deg silicone bend all blends in. I suspect a lot of the trick will be to cut the right amount and best positioned bits of the hoses, but at the end of the day the bypass hose has some flexibility so it should fit.

Ok some updates on the cooling project, including some useful information for those who (may) follow!!

Both engine side metal outlet and inlet are 38mm connections.
Both top and bottom radiator outlet and inlet are 35mm connections.
The PEL500110 has 35mm connections for in (from radiator, lone connection), out (to engine, angled connection) and 32mm for the bypass input (from top-hose Tee, straight connection of pair).

I'm using 32mm for the bypass which matches the landrover thermostat bypass gauge of 32mm.

Top hose:
The current plan for the top hose is to use a 35-32-35 T in there. An alternate to cutting the Toyota hose (as the radiator angle is mid way between 45 and 90 degrees) is to find a rare 60 degree bend like Samco make. The engine side bend is 45 degrees so you can use a silicone or the original.
Because you'll cut only the top hose, do the bottom hose and critical bypass routing first - no need to burn the bridge.

Bottom hose:
This is replaceable by a straight 38-35mm reducer onto the thermostat and a 45 degree 35mm angle from the thermostat to the radiator outlet.
This means you can lay your Toyota bottom hose aside as a spare: it's not needed (and is in fact the wrong shape to splice the thermostat into).

Bypass
This is the complex one (all in 32mm) and needs a 100mm legged 45 degree silicone pipe from the thermostat to dive down under the main pulley to sit just behind the crossmember, a long legged alloy 90 degree bend to come up next to the main pully on the top-hose side - to be secured with a P clip to a handy steering pump bolt, then up to the tee piece on the top hose.

BTW this is all only possible with the fan, shroud and overflow bottle out of the way, unless you have the arms and hands of a small child or Inspector Gadget. The fan is held on with 4 12mm M6 bolts so use a little WD40 and care as you don't want to strip them. I plan to replace with mild torque only and a dab of blue threadlock, or you could use washers and nyloc nuts I guess.
Then you can unclip the top part of the shroud and put that aside. Then undo the bolt for the bottle and the two bolts for the shroud.
Then get the top hose off because the bottle is NOT coming out with it still there.
Then disconnect the low-coolant sensor and with endless patience you'll be able to lift and turn anti-clockwise the bottle to get it out - sliding it out past the timing chain cover. Get someone else to hold any light, you'll need two hands for this.

The fan shroud is a similar diabolical puzzle and ideally needs one person each side to guard the auto cooler lines etc. It will only come out in one piece if you rotate it up at the bottle/top hose side and down at the bottom hose side, almost jammed between the metal and the cam chain cover. It will bend slightly to help the corners clear stuff. You may want to remove the tinware below the radiator before to give it a little more room, 4 12m bolts from under the van's steering rack.
Good luck.

Initial testing of the Landrover cooling method on the Hiace:

So after a lot of to-ing and fro-ing the new system is in and has a few miles under it's belt. Not many miles - not enough to prove reliability, but the operation can be proven.

Note that I used the PEL500110 Landrover pressure sensitive 83C thermostatb for this conversion.
The hose parts you need are:

1. 45 degree tight angle (silicone) for the top hose into the Tee. This will be cut as short as possible

2, Aluminium 35-32-35 T to provide the bypass flow to the thermostat

3. Straight radiator hose 34cm of 32mm  (e.g EPDM W.P. 4 bar).

4. Original rubber tophose from radiator, cut to allow the Tee and bypass (down-pipe) to miss the water overflow bottle by about 5mm. This hose is vibrating so must not touch the fixed tank.

5. Aluminium 90 degree swept bend: this must fill a 18cm square - bigger is also fine i.e. 20cm). I.e. it has to have very long legs. This goes from the bypass downpipe to the 45 below.

P-clip for the above 34cm long downpipe bypass hose, and a P clip for the aluminium bit. This is to attach 1. to the bolt in the steering pump to hold the pipe rigid against the engine, and 2. via a 50mm M6 hole-to-hole 45 degree twisted strip to a sump bolt to make sure it doesn't get any ideas about moving forward and chafing on the crossmember.

6. 32mm 45 degree pipe with 100mm legs (ideally one leg can be 120mm, one will be cut down). This connects the thermostat bypass in to the aluminium pipe.

7. The PEL500110 thermostat, the pair of openings side to the engine, single side to the radiator outlet.

8. 38mm - 35mm reducer silicone cut to 90mm evenly around the size change. This goes from the old thermostat casting to the new thermostat.

35mm 45 degree bend cut as suited to connect the thermostat to the radiator.

Important tip: Position all the jubilee clips so you can access the heads from under the car, because when the engine cover, fan and shroud are back in it's a bit tricky when you want to check they are tight enough. Do not overtighten, it's silicone and plastic.

Preparation
Check around ALL the pipes that there is room and no chafing. The engine is continually vibrating and care must be taken to prevent stuff from wearing and rattling.

Notes
Note that I have my modified temperature gauge and only a wild guess as to where 'normal' was. I also have not fitted the digital gauge I got as I couldn't find anywhere to screw it in and was too busy to solve that one. With the temperature gauge modification I can however see every single temperature fluctuation and 'normal' now with this thermostat is just at the top of the thermometer symbol. This is so stable it is obviously the thermostat point (83C) so the head temperature is probably around 86C.

Note also that my dummy thermostat is the old Toyota thermostat with the core removed but bolts and washers simulating a cold state of the bypass plate at the bottom, so the old head bypass is allowed to flow as if there is a cold position thermostat. I felt this was important because it diverts the flow away from the pump and allows it to mix better with the water coming in the side, now unimpeded. I removed the jiggle pin so it also has the bleed hole at the top.

Note that this system took about 11 litres of coolant to refill. Buy concentrate Toyota red long life coolant and mix 1:1 with Tesco deionised water £1 for 2.5 litre tubs.

Note: This system was ridiculously easy to bleed, coolant poured in the cap flows down both sides of the T piece and into the head leaving no air pockets, although you may wish to test the heaters to bleed them.

Note: This is a high flow system, at all times and temperatures the head has an even stream of water moving along it and exiting both sides - into the internal bypass and into the T-piece, from which the Landrover thermostat will choose how to mix water from the bypass and radiator to blend into the engine cooling inlet.

Note: Although fitted on the radiator output this is NOT a slow thermostat like the old one. It will open with pressure (high revs) and also the fat 32mm bypass means that it receives water at head temperature continually at a fast flow.

Initial Testing
Only tested in hot weather so far!!
Initial warmup is gentle but definite.
Once the operating temperature is reached the (corrected) temperature gauge has a range of only around 1mm, dropping slightly down leafy hills and rising slightly when working. It's amazingly stable.

So initial impressions are very good. It's a bit of a job and probably not really necessary in the UK but if towing or exploring hot and/or mountainous areas it should in theory be much kinder on the engine, and possibly more economical too - I'll have to see what I get!

No photos yet as I changed phones.

Good wright up GPW this mod is on my list on mine I have a digital gauge normally engine runs at 80deg to 86deg dependent on incline, when towing up steep hills in hot weather can reach 110 deg but then second fan comes in and never goes higher just wondering if this is too high for safety what do you think .

JT69 wrote:

Good wright up GPW this mod is on my list on mine I have a digital gauge normally engine runs at 80deg  to 86deg dependent on incline, when towing up steep hills in hot weather can reach 110 deg but then second fan comes in and never goes higher just wondering if this is too high for safety what do you think .    

I bought the digital gauge but didn't have the time to fit it - especially the business end that measures the head temperature - I noticed the factory sender goes right into the head itself (although the gauge is damped as per other thread).

I think the way the temperature changes is more important that the actual temperature - but 110 does seem a bit warm - I'd not want it to top 95 ideally if it was me. But the top cooling limit will be determined by the condition of the radiator(s), pipes, pump, coolant, fan and thermostat etc rather than topology as the thermostat should already be wide open then.

My sender is fitted in the top hose next to filler cap reading does not move untill thermostat opens then appears to be quite sensitive to engine load even on motorways in top gear you can tell if there is an incline (my favorite trick is slip streaming trucks works wonders for the MPG when towing a race car trailer) and keeps temp down.

JT69 wrote:

My sender is fitted in the top hose next to filler cap reading does not move untill thermostat opens then appears to be quite sensitive to engine load even on motorways in top gear you can tell if there is an incline (my favorite trick is slip streaming trucks works wonders for the MPG when towing a race car trailer) and keeps temp down.

I was thinking of buying a top-hose sender adapter but my top-hose is now rather busy with the 32mm bypass Tee piece so there's no space there now. TBH the new undamped gauge is so sensitive that the pressing need for the digital gauge is now just a 'nice to have' feature so there's no rush

Great write up ! You wouldn't happen to have any pictures of the install by any chance ?

Cheers

GPW wrote:

Ok some updates on the cooling project, including some useful information for those who (may) follow!!

Both engine side metal outlet and inlet are 38mm connections.
Both top and bottom radiator outlet and inlet are 35mm connections.
The PEL500110 has 35mm connections for in (from radiator, lone connection), out (to engine, angled connection) and 32mm for the bypass input (from top-hose Tee, straight connection of pair).

I'm using 32mm for the bypass which matches the landrover thermostat bypass gauge of 32mm.

Top hose:
The current plan for the top hose is to use a 35-32-35 T in there. An alternate to cutting the Toyota hose (as the radiator angle is mid way between 45 and 90 degrees) is to find a rare 60 degree bend like Samco make. The engine side bend is 45 degrees so you can use a silicone or the original.
Because you'll cut only the top hose, do the bottom hose and critical bypass routing first - no need to burn the bridge.

Bottom hose:
This is replaceable by a straight 38-35mm reducer onto the thermostat and a 45 degree 35mm angle from the thermostat to the radiator outlet.
This means you can lay your Toyota bottom hose aside as a spare: it's not needed (and is in fact the wrong shape to splice the thermostat into).

Bypass
This is the complex one (all in 32mm) and needs a 100mm legged 45 degree silicone pipe from the thermostat to dive down under the main pulley to sit just behind the crossmember, a long legged alloy 90 degree bend to come up next to the main pully on the top-hose side - to be secured with a P clip to a handy steering pump bolt, then up to the tee piece on the top hose.

BTW this is all only possible with the fan, shroud and overflow bottle out of the way, unless you have the arms and hands of a small child or Inspector Gadget. The fan is held on with 4 12mm M6 bolts so use a little WD40 and care as you don't want to strip them. I plan to replace with mild torque only and a dab of blue threadlock, or you could use washers and nyloc nuts I guess.
Then you can unclip the top part of the shroud and put that aside. Then undo the bolt for the bottle and the two bolts for the shroud.
Then get the top hose off because the bottle is NOT coming out with it still there.
Then disconnect the low-coolant sensor and with endless patience you'll be able to lift and turn anti-clockwise the bottle to get it out - sliding it out past the timing chain cover. Get someone else to hold any light, you'll need two hands for this.

The fan shroud is a similar diabolical puzzle and ideally needs one person each side to guard the auto cooler lines etc. It will only come out in one piece if you rotate it up at the bottle/top hose side and down at the bottom hose side, almost jammed between the metal and the cam chain cover. It will bend slightly to help the corners clear stuff. You may want to remove the tinware below the radiator before to give it a little more room, 4 12m bolts from under the van's steering rack.
Good luck.

Yes! I got them off my old phone now so here they are!

Looking down to where the new thermostat fits

The 'sideshoot' goes to the pipe to the engine where the old (now open) thermostat lives. The main centre shoot curves off to the 90 degree metal curve that sweeps up toward the Tee. The single pipe is the inlet from the radiator.

The thermostat monitors the temperature and pressure of the hot water from the engine and the cool (sometimes heated by the transmission) water from the radiator and opens to the radiator when required, mixing the result (like a mixer shower) into the engine through the sideshoot.

Looking forward to the radiator, note the transmission auto-cooling line above.


The bypass into the thermostat arrives behind the main pulley, the metal curve held in place by a P-clip to a bolt on the sump (added after picture). The bottom of the vertical rubber pipe is held in place by a P-clip to a bolt on the steering pump (the big shiny band in picture. These two P-clip anchors prevent the pipes touching the chassis or fan.


Bypass pipe running from a Tee at the top, 32mm radiator pipe.


Summary views after fan reinstallation


Note on my van I replaced the old thermostat centre with washers and bolts to simulate an open thermostat (i.e. a disc a few mm away from the internal head bypass drilling), so that the internal bypass water from the head mixes nicely in the block around the oil cooler - but it probably doesn't really matter.

With a modified undamped temperature gauge I get a smooth warmup and the needle only moves around 1mm between racing up a hill and coasting down the other side, so remarkably stable. Ultimate cooling is of course still governed by the condition of the rad, pump and fluid.

That's awesome thanks so much ! I'll be doing this mod soon.

No worries, keep the thread updated on how it goes.
You'll need access to the underside, so don't start until you have it, it's needed to check the pipe routing and that the metal bend is safely clear of the pulley and captured by the stainless P clip.

Before you try it you may want to modify the temperature gauge to remove the huge dead-spot in the middle - it's dangerous and not required after this mod.
See:
https://hiace-super-custom.forumotion.com/t3426-modding-the-toyota-temperature-gauge-no-zener-dead-zone
Note - if you use the values of resistor I give in that thread the needle sits at around 10 O'clock when warmed up as I didn't quite know the 'normal' thermostat position I was aiming for so I had to guess.
At some point now I know I'll adjust the values so it sits at 9 o'clock for normal.

Sounds good. I may opt for an aftermarket temp gauge as well. Thanks for all the info !

Tremendous post and hugely detailed. I just came here looking for some coolant details but will pour through this when I've got a bit more time.

Just a small thing I've noticed is that it seems the thermostat on the 3L and 1KZ engines operate at quite different temps: https://www.hiacesoutheast.com/store/cooling-system. Interesting