Hot Hot Hot 1KZ Engine

Hey folks,

Our 1998 KZH128 campervan with the 1KZ-TE engine has in the last few days been overheating something fierce on the drive down the Pacific Coast Highway i Northern California. Coolant has to be replenished frequently, sometimes several times a day on longer drives with big hills. Engine temperature goes up to the red zone on steep hills and Automatic Transmission Oil light comes on from all the heat. Of course we pull over to cool down, but it is happening more & more frequently and we are at a bit of a loss.

We've been driving the coast for a month and a half with little trouble, but the last few days have been an overheating apocalypse.

We had the Hiace checked out at our garage back home before heading out on the road trip and all was reported well except for a 3 pound drop in coolant line pressure. 'Nothing to worry about' we were told but, well, here we are with plenty of worries.

A local garage thinks that the head gasket may be the culprit but they have no Hiace experience and I would like to ask if anyone here has had a similar problem. Any suggestions are welcome, we need to find the problem and are a long way from home!

Cheers

Hey, good evening.

Wonder why a pressure loss is no big deal? If it is evident in testing something is wrong. Should hold with no drop for a half hour.

We are in the PNW too and I made some careful mods to keep my wife’s Hiace running cool. However if you are experiencing coolant loss with no external leaks evident the leak is likely internal. Cracked head, head gasket, etc. none of that is fun.

There is nothing special about a Hiace for diagnosing this. Combustion gases will escape into the coolant and simple testers catch them every time.

If your engine is sound, all we did was put a (10 bladed?) different Toyota fan they put on hot climate models. A fresh blue fan clutch. Fresh coolant. New temperature sensors and I rebuilt the front horizontal radiator power pack with new seals and a significantly more powerful cooling fan assembly.  Hers runs great now. Just needed that little extra help.

Bottom line, it’s a simple diesel with a traditional cooling system. Diagnosing it should be trivial for a reputable shop. Getting parts and fixing it are much more challenging if it’s broken inside here in America.

I hope your van isn’t broke. Good luck

-Bryan

Hello.

Do you have the part number for the 10-blade fan, and is it still ~400mm in diameter?

Thanks

The part number is 16361-54131

Maybe 100 dollars.

It’s the stock diameter and everything.

Hope you have an awesome weekend,

I suspect the fan drive is non functional.
You'll need to listen, be careful, when warm, they should be moving a LOT of air.

If not, the fan boss needs refilling or replacing.
Look for youtube videos of people refilling them with the silicone drive fluid.

Old fan clutches can cause all sorts of problems. But the OP is experiencing coolant loss without an obvious external leak.

It’s important to focus on where it’s going first before looking at coolant fans. Start at one end of the problem, test while moving to the other end. It absolutely could be anything at this point, but we know the coolant system isn’t holding pressure or coolant. In those situations good news is hard to find. I hope it’s something small too, but the OP should be prepared for internal engine damage.

Hello.

I’ve thought about responding to this post on a couple of occasions but the danger is it reads like: “it could be this or it could be that”. I also wonder about the fan clutch as if faulty it will limit active coolant cooling but there could be plenty of other problems, not least small issues or long-term degradation that has been exacerbated by changes to warmer environmental conditions etc. For example my van was holding pressure but the cooling system had suffered neglect such that I expect driving up long hills in hot climates would lead to overheating. I’ve written a long post here:

https://hiace-super-custom.forumotion.com/t4317-my-lh119

that might be useful and was written as I wanted to document the issues with my van and many posts on this forum relate to cooling so opted for the post once refer to often mantra.

Anyway as initially stated and reiterated will_hiace’s van seem to need the coolant topping up without obvious external leaks.

I’d go about this by establishing definitively that there are no external leaks. The cooling system is not sophisticated but on some vans there can be a lot to it with one or two engine cooling radiators plus one or two cabin heater matrixes, a transmission cooler(?) and associated pipework that goes front to back and side to side, plus it can be difficult to view and access. Rear heaters can leak into the air ducting and front ones into the carpet. Pipe clamps can fail and solid and flexible pipes weep or leak. I’d also include a faulty pressure cap as an external leak though leaks here can be due to the cap or issues elsewhere in the system. Finally here, water pumps can get clogged or leak externally, but this isn’t where I’d start. Hopefully you have a not obvious external leak that’s easy to find and sort.

If you definitely have no external leak then it’s likely to be a head gasket or in the engine somewhere. If combustion gasses are getting into the cooling system then this can be tested with chemicals (and it’ll likely lead to overpressure, too). If coolant is getting into the cylinders then it’ll probably be evident in the exhaust gasses (and make the exhaust smell different, too). If coolant and oil are mixing them you can get the typical mayonnaise-product, but you can have head gasket problems without this being apparent. With almost all head gasket issues there tends to be a power drop or misfire, too.

Btw, thanks to blgravely for the 10-bladed fan part number. It checks out on both the Amayama and Autodoc sites. Of note, the Autodoc site lists an AISIN part for ~£37 and it’s probably an AISIN part that’s fitted as OEM. Almost every ‘catalogue’ part on my van is either AISIN or DENSO so I presume Toyota just uses them as their preferred supplier and sticks them in a red-labelled box or bag if you buy from the dealer. For the UK Autodoc ships orders >~£120 without extra fees so I think I’ll add the 10-bladed fan to my next order from them.

HTH

The fan clutch is also an Aisin FCT-004 (blue) off 90s land cruisers sold here if it tests bad

Thanks to all for the great advice & tips, here is where I stand so far:
- No obvious leaks to explain where the coolant is going;
- I received a tip from a Hiace knowledgeable mechanic to start the van from cold with radiator top off and watch radiator top to see if there is any bubbling (indicating, I am told, that there are likely exhaust fumes getting into coolant which could indicate a head gasket problem)
- I performed the above step and, after running engine at idle for about 15 minutes there was indeed evidence of bubbling through coolant;
- I have also heard of a Combustion Leak Test (essentially a tapered tube that fits into radiator opening, fill with blue liquid and presence of exhaust gas would turn liquid green/yellow)
- This could be my next step.
I would be 'happy' to find that there issue is 'not' the head gasket as that would seem to be the most costly to repair, and the nearest Hiace knowledgeable garage is 150 miles away over steep & rolling hills

Speaking from experience with the 1kzte engine not the present one in my Hiace but a previous one in a Prado/Colarado but do now what to look for. Alas it would appear you do indeed have a cracked head, so did I in my colarado , a few diagnostic steps will confirm put a plastic tube on the outlet pipe of the expansion tank place the end in clear bottle of water if bubbling occurs at operating temp or at all you have a cracked head . Look at the oil on dip stick if it is coffee colour you have a cracked head also if there is coolant coming from exhaust pipe you have a cracked head . Sorry but there is no alternative but to fit a new cylinder head (other than scraping the vehicle) complete with new gasket and head bolts .I did mine as a DIY project and still cost £700 not cheap . As above have stated its essential to make sure the cooling system is working correctly or the engine will overheat again causing the new head to crack they are obviously unable to resist over heating cycles.

Yep it is THE most common fault with the 1KZ. Cracked head. Guaranteed that every 1KZ from the mid 90’s will require a replacement head at some stage after 15 years 250,000kms. I was told by the local dealer that Toyota were onto their 5th version of the head when I replaced mine with genuine head. Apparently there was a design problem with the coolant passages.

The other part worth checking is the thermostat. If it is stuck closed (rare failure) it could cause similar symptoms. Pain in the arse to change on the van.

The classic test for diagnosing head failure in these vans is that it may drive perfectly fine around town and maybe even up to 90kph but as soon as it is pushed a little, uphill or more speed, the heat spikes up and fluid is pushed out the overflow.

The weird thing is that they often pressure test fine and you won’t necessarily see bubbles in the overflow or the radiator fill point. I actually rigged up hose to the expansion overflow that fed a coke bottle jammed in the frame up under the front and I would pour it back into the system every other morning. Could see at a glance up under the front passenger wheel whether fluid was in it and pushing the engine a bit hard was like a switch to pressurising the fluid out.  Drove like that 3 months until getting all the parts together.

Additionally, once you see the heat warning on your trans, the trans-fluid has a much shortened lifespan. Aim to change that after head fix.

blgravely wrote:

Hey, good evening.

Wonder why a pressure loss is no big deal? If it is evident in testing something is wrong. Should hold with no drop for a half hour.

We are in the PNW too and I made some careful mods to keep my wife’s Hiace running cool. However if you are experiencing coolant loss with no external leaks evident the leak is likely internal. Cracked head, head gasket, etc. none of that is fun.

There is nothing special about a Hiace for diagnosing this. Combustion gases will escape into the coolant and simple testers catch them every time.

If your engine is sound, all we did was put a (10 bladed?) different Toyota fan they put on hot climate models. A fresh blue fan clutch. Fresh coolant. New temperature sensors and I rebuilt the front horizontal radiator power pack with new seals and a significantly more powerful cooling fan assembly.  Hers runs great now. Just needed that little extra help.

Bottom line, it’s a simple diesel with a traditional cooling system. Diagnosing it should be trivial for a reputable shop. Getting parts and fixing it are much more challenging if it’s broken inside here in America.

I hope your van isn’t broke. Good luck

-Bryan

This is really good stuff!

blgravely wrote:

Hey, good evening.

Wonder why a pressure loss is no big deal? If it is evident in testing something is wrong. Should hold with no drop for a half hour.

We are in the PNW too and I made some careful mods to keep my wife’s Hiace running cool. However if you are experiencing coolant loss with no external leaks evident the leak is likely internal. Cracked head, head gasket, etc. none of that is fun.

There is nothing special about a Hiace for diagnosing this. Combustion gases will escape into the coolant and simple testers catch them every time.

If your engine is sound, all we did was put a (10 bladed?) different Toyota fan they put on hot climate models. A fresh blue fan clutch. Fresh coolant. New temperature sensors and I rebuilt the front horizontal radiator power pack with new seals and a significantly more powerful cooling fan assembly.  Hers runs great now. Just needed that little extra help.

Bottom line, it’s a simple diesel with a traditional cooling system. Diagnosing it should be trivial for a reputable shop. Getting parts and fixing it are much more challenging if it’s broken inside here in America.

I hope your van isn’t broke. Good luck

-Bryan

Bryan, could you share more details on the “front horizontal radiator power pack”, not sure I know what that is? Is the “more powerful cooling fan assembly” and electric fan separate from the upgraded 10 blade engine powered fan? Also any intel on the new temp sensors would be greatly appreciated. This sounds like a really good upgrade that would be helpful here in New Mexico!
Chris.

Hi

The front horizontal cooling pack is a sandwiched condenser and auxiliary radiator assembly suspended in the front right behind the bumper. It has an electronic fan on top that is fed by a ballast on the drivers side. It activates when the AC is on along with full speed operation when the engine gets 215/220 ish. That temp sensor is on the water manifold by the radiator cap. Ground it out and the fan comes on is the test to see if you have the right one.

Ours had a bad condenser fan and the gasket between was allowing air to escape when I could get it to come on. It’s a pusher assembly and I couldn’t source a replacement.

So I broke the assembly apart and resealed the 2 halves with weatherstripping. Then I put a 2 speed derale electric cooling fan off my race car because it fit perfectly. I’ll attach pictures below.

The 10 bladed fan is a Toyota part they put on the 1KZ’s in hot climates. It fits perfectly.

Her van doesn’t smoke, the AC is ice cold and it doesn’t overheat even when you wood it up the 3 mile hills we have up here.

I will say that the temp sensor is very slow to react even new. If yours is bad if memory serves I put a NTK Sensor off a 90s Toyota on it. It’s used on a ton of Chevrolet and Toyota models. I’ll find it in a bit.

Hope this helps. If you have more specific questions I can punch you in the right direction (I think) just know that assembly is very challenging to get to.

Good luck everyone!

Have an awesome summer ahead

I will say of you go this route or similiar, the new fan is much more powerful and much much quieter. It’s like 2400CFM to the stock 8/900 ish.

It blows leaves around when it’s on haha.

It really helps with the AC too.

blgravely wrote:

Hi

The front horizontal cooling pack is a sandwiched condenser and auxiliary radiator assembly suspended in the front right behind the bumper. It has an electronic fan on top that is fed by a ballast on the drivers side. It activates when the AC is on along with full speed operation when the engine gets 215/220 ish.  That temp sensor is on the water manifold by the radiator cap. Ground it out and the fan comes on is the test to see if you have the right one.

Ours had a bad condenser fan and the gasket between was allowing air to escape when I could get it to come on. It’s a pusher assembly and I couldn’t source a replacement.

So I broke the assembly apart and resealed the 2 halves with weatherstripping. Then I put a 2 speed derale  electric cooling fan off my race car because it fit perfectly. I’ll attach pictures below.

The 10 bladed fan is a Toyota part they put on the 1KZ’s in hot climates. It fits perfectly.

Her van doesn’t smoke, the AC is ice cold and it doesn’t overheat even when you wood it up the 3 mile hills we have up here.

I will say that the temp sensor is very slow to react even new. If yours is bad if memory serves I put a NTK Sensor off a 90s Toyota on it. It’s used on a ton of Chevrolet and Toyota models. I’ll find it in a bit.

Hope this helps. If you have more specific questions I can punch you in the right direction (I think) just know that assembly is very challenging to get to.

Good luck everyone!

Have an awesome summer ahead

I see, i knew about the e-fan cooled condenser behind the bumper, and now I understand the seals you replaced were weather stripping, thought they were some internal seals I wasn’t aware of. Will appreciate the sensor info. Is there a model number or size for the derale fan? U must have order the 10 blade fan from over seas? Super excited about this mod! How did u figure it out?

Hey buddy.

Got the 10 bladed fan and sensor from megazip (Japan)

P/no’s:
Sensor: 89428-20100
Fan: 16361-54131

The electric fan and shroud is a derale 16816. It’s a pretty nice 17” fan and shroud. Dimensions are 16-3/4''W x 17-5/8'' x 3''D. Actually fit perfect for some strange reason.

I just was wanting her van to be reliable and still look original. Let it keep that Japan charm. But it’s cooling system was weak coming from an island that doesn’t get hot and the speed limits are low. It has a ton of coolant in the system but not much in the way of airflow. Instead of reinventing the wheel I thought I would try this first.

If it didn’t work I was going to put a single aluminum race car radiator and a huge fan in front of the engine and never worry again. But thankfully this has worked perfect. I am tempted to put a PWM controller on it this summer so the fan can go from 0-100 instead of the 2 speed step it has now. I did that on her Tacoma and it works great.

If your Hiace is getting warm, try getting more air to the radiators like I did. It worked for us and I hope it can work for you too.

Have a great night
-Bryan

blgravely wrote:

Hey buddy.

Got the 10 bladed fan and sensor from megazip (Japan)

P/no’s:
Sensor:  89428-20100
Fan: 16361-54131

The electric fan and shroud is a derale 16816. It’s a pretty nice 17” fan and shroud. Dimensions are 16-3/4''W x 17-5/8'' x 3''D. Actually fit perfect for some strange reason.

I just was wanting her van to be reliable and still look original. Let it keep that Japan charm. But it’s cooling system was weak coming from an island that doesn’t get hot and the speed limits are low. It has a ton of coolant in the system but not much in the way of airflow. Instead of reinventing the wheel I thought I would try this first.

If it didn’t work I was going to put a single aluminum race car radiator and a huge fan in front of the engine and never worry again. But thankfully this has worked perfect. I am tempted to put a PWM controller on it this summer so the fan can go from 0-100 instead of the 2 speed step it has now. I did that on her Tacoma and it works great.

If your Hiace is getting warm, try getting more air to the radiators like I did.  It worked for us and I hope it can work for you too.

Have a great night
-Bryan

Thank you so much. Here is a dude i follow on YouTube, he has got some helpful tips. He replaced his radiator with an aluminum one. Will do your mods first, and keeping radiator replacement as a last resort. https://youtu.be/lyKTAG1bums

Agree totally. It’s more expensive this way, but I think we’d both be happier with the Japanese setup working great vs a race car setup.

I don’t know what I’m going to do if the radiators ever fail though. Fingers crossed they have decades still in them.

Good luck. I think you’re going to be really happy soon.

blgravely wrote:

Hey blgravely,

I was curious what the wiring process looks like for installing this fan. Is it as simple as plug and play? Thanks

blgravely wrote:

The flip flops are back !