Overheating only at higher rpms

Hey good folks of the forum,

After digesting all I could from this forum and consulting most of the people I know who know a thing or two about engines, I have to lay out my struggles.

LH107W-MFPQS with the 3L has been running fine for me up until about a week ago. Drove it from LA to Washington state after buying it without a hitch, then from Washington down to Utah where I moved to recently. It's been doing fine in all respects, but on a recent trip to Colorado the coolant light came on during the drive home. Didn't identify it properly at the time, nor was there any place to stop for coolant, and drove home with the light flickering on and off at intervals.

Didn't overheat on that drive, nor subsequent drives after topping off. I drained the radiator out of the standard petcock, then refilled, but I did not get the engine drain bolt as I have read here might be necessary, so I don't think I actually got it all.

It drove fine around town in the days after this, but when I drove twenty minutes up a hill on the highway at a steady 3000-3500 rpms to try to get up to the speed limit, I noticed the temp gauge was blinking at the top of the guage... Pulled over, coolant boiling over in expansion tank, and I let the engine cool at idle, which it did in 10ish minutes, then coaxed it out to where I was working that evening and let it idle for 20 minutes, which it did at normal temps.

Drove it home that night and since it was downhill it was fine. I've read about the bad thermostats, dampened viagem, and inherent flaws in the cooling system, and I have a fresh tsat ready to pop in as soon as she cools down from running her with coolant flush and distilled water in the tank. Planning to do a full flush (does this mean I need to take off the skid plates and loosen the engine drain bolt?), replace thermostat, and see what happens, but I have the worst possible scenarios of a broken head running through my mind...

Could this be a simple thing of replacing the tstat and flushing, or does this smell like bigger trouble to you all out there? Thanks in advance for your help, I'm hoping to get to the bottom of it as fast as possible, even if it is what I don't want to hear... No sense hiding from reality and messing up the engine more.

So I got a tip from the guy I do drywalling for, his neighbor here has a small auto shop and has worked on some delicas, the other popular JDM van imported into the US, he seemed a little wary, but gave me the name of a shop in town that he said will work on "exotics".

Called the shop and talked with a guy who told me his own struggles of importing a WRX, then having to stuff it into a US body in order to have a valid VIN. We talked about the struggles of lack of info, and he suggested delving into Japanese forums, or even giving my Japanese friend a call for help. Definitely inspired confidence that he knew what he was getting into, and have a diagnostics appointment in a couple weeks (small town of Moab, Utah with lots of 4x4 trails nearby means busy shops), but hopefully I can get things hammered out myself before then.

Did another flush with the thermostat out, going to replace the thermostat this evening and get into the engine block drain bolt. Also, I'm still unclear if I have one or two radiators, I saw on jp-carparts that the other assembly I have parallel to the ground might be the heater/ac assembly, but the fans aren't spinning when heat is on. Other forums I've read have said that 4wd models usually have the 2 radiators, but I've read on this one that it's mostly the 1kzte and I have the 3L.... So many questions and all my reading just gives me more.

Still hoping to hear from anyone out there who this sounds familiar to, and still combing the archives for hints, but it seems like all the threads I find fizzle out without resolution, and since I can't search posts by username, I can't ever track down what happened to these people and their vans!!

Thanks, and hope to hear from yall soon.

Just a thought: did you remember to turn on the heater when you refilled the coolant to prevent an air-lock in the pipes? And yes you will need to drain the block if you want to do a thorough clean / flush. Refill with the correct coolant mixture (ours needs the RED coolant but is a lot earlier model to yours so yours may be different) to prevent corrosion. Ours has only one radiator for the engine, which we just had to replace due to rust, and the horizontally mounted radiator underneath is just for the A/C.

If in doubt fit a new fan, these vans need a fully working viscous fan to not overheat.

Thanks for the tips...

I did have the heater going when burping and the fan seems to be doing fine (as far as I can tell).

I did manage to get to the engine drain bolt last night, but managed to royally screw myself over when replacing the thermostat. I figured I'd use the old gasket, run it for 15 minutes for another flush, then use some gasket maker when it cooled down later to let it dry overnight... I filled it up and started to see water dripping down the engine block in small stream, started freaking, thinking I found the leak, only to realize it was coming through coolant outlet gasket. I tried to torque the bolts down a bit more, but ended up cracking the outlet due to unevenly torquing the bolts in my panic.

Now I am waiting on a part coming from the UAE, $70 with expedited shipping and it still won't be here til next Tuesday at the earliest.

Plenty of time to twiddle my thumbs, buy a proper torque wrench, and worry. I think maybe I screwed myself by using some Bars Leaks coolant sealer product when I initially did the coolant change. Not draining the block coupled with putting more gunk in may have been causing some nice blockages.... At least the YouTube nightmare stories I watched about stop leak stuff has me thinking this.

Still no signs of water in oil/exhaust in coolant etc. So hopefully it's just wait for the part, flush one or two more times and smooth sailing.

Will keep you all posted, and thanks for the replies.

Oops!

You can get gasket material you cut out to size, may be a good idea.

BTW the fan always spins, but you should hear it moving some decent air when warm and feeling the wind standing near the engine.

That's a good point, I will have to check it's speed when I get it back up and running.

I just feel like logically since this problem coincided with a coolant change, especially one in which I used the bars leaks stuff, it has to be related to that more than the fan....

Coolant system working, change the coolant, starts overheating... Doesn't make sense that it would be the fan to me, but I've been misled by my "logic" plenty of times before.

Well, I'm going to try to distract myself this week since I can't do much of anything till I get the part, but I'll report back when I do

I'm with GPW that it's definitely good to confirm correct operation of your radiator fan. It could be the viscous coupling on the fan is not engaging as the coolant temp is climbing. You can hear an audible increase in white noise (and slight decrease in power) from the engine when the fan's RPM increases. When the viscous coupling gets hot enough, it locks the clutch to match the pulley speed versus allowing for slippage at lower tempts (fan still spins, just not as fast).

I just got back from the beach, having to traverse our coast range each way, and on the climb (2nd or 3rd gear @ 3000-3500RPM depending on the grade) the temp on my aftermarket water temp gauge would start climbing into the high 190Fs and sometimes to ~205, and then the fan would spin up, and the temps would drop 5-10F rather quickly. I can imagine if the fan didn't speed up that the coolant temp would become critical in short order. There are threads online via the tacoma/hilux forums about servicing the viscous coupling, looks to be a bit of a pain, but you have to take the fan off either way to repair or replace.

I had to smile when you said you were trying to get up to the speed limit. I have resigned to the fact that I'm the slowest vehicle on the road, and don't even try to get up to the speed limit when not on the flat, just whatever speed the van decides it can manage. Have gotten to know the O/D Off button quite well

I was reading your post again and I'm wondering if some corrosion broke loose during the drain/refill and has partially blocked a pathway. When I did my flush, I drained the rad and the block, and then removed the thermostat and used a pool/spa pre-filter attached to the end of my garden hose to flush the rad/block under some pressure. I just pressed the pre-filter against the water outlet opening to create as best a seal I could and un-kinked the garden hose. I definitely got some scale/flakes coming out from that effort, though nothing too big. I then flushed with distilled water and a coolant flush treatment product before adding coolant. Perhaps trying this on your next flush might help dislodge any blockages?

Hmmm, that's definitely a possibility, and like I said, I'll be checking the fan more closely when I get this damned coolant outlet next week.

Also, yeah, the color has changed significantly from the first drain to the last couple flushes. It's coming out clear and steady now, and a lot of the crud from that stop leak stuff is coming out as well. I'm hoping that with a new thermostat and such will help solve any kinks in the flow, as I know it's not a bad water pump.

Is it bad to let it sit with an empty coolant system after flushing with distilled water? As in, if I let it sit empty, will it be at more of a risk of rusting than if I fill it with coolant?

Not sure it'll rust much over a few days, you could always tape over the open holes so no new air can get in.

Also remember to flush the rear heater matrix if fitted too, I found mine was quite silted up when I took it out (as part of a camper conversion, it was still working well!).

Noted, I will check the manual tonight after my second job is over and see if I can locate that... Does it have a separate drain bolt?

Coolant has anti-corrosion additives in it, so I would think that it would be better to not have it sit empty, or full of just water for very long. Not sure how much of a problem leaving it that way presents for just a few days, but I would maybe put 10% coolant / 90% water in the interim just to be safe?

While you wait, here is a really interesting article on the coolant/water ratio: https://www.sparkplugs.com/learning-center/article/653/quest-for-the-ideal-coolant-ratio

The rear heater matrix has a mix of soft/hard lines running down the driver's side of the van, which enter the body just ahead of the rear wheel. You could disconnect one of the lines sending coolant towards the matrix at a hard/soft junction and force flush from there. You can identify which line is the sender as it will have a valve body inline near the rear wheel that is actuated by the heater controls in the 2nd row trim panel. GPW may have a better method, as he's been tinkering on these vans far longer than I!

The rubber hoses to the rear matrix were pretty easy to remove on mine so I'd disconnect them both and flush the matrix on it's own with a hose.

If you're ok at draining and filling the system you may as well flush the matrix and then immediately refill most of the system as the bit you are waiting for sits at the top anyway.

Yeah GPW is a powerhouse of info from all I've read on this forum, and that info is much appreciated. I will look into doing that this weekend, I think I may opt to not go on a climbing trip with my roommates in favor of doing some prep work on the coolant system for when I get the coolant outlet next week...

Also worth noting is that I found a streak of rust colored coolant last night coming out of a small hose on the top left (when facing out the windshield) of the radiator that looked fresh since I could wipe it away with my finger. I'll be replacing that hose and clamp, but how much of an impact could that have on the system? If it reduces the pressure somewhat that could cause a lowering of the boiling point in the system if it's not getting up to pressure, right? I'm hoping with all these minor things I'm finding it could add up to the larger problem, but I'll find out more when I get it all back together next week.

Thank you all so much for chiming in here, I'll be keeping you posted as things come back together here in the coming days.

I don't really know that much about the vans, I just seem to end up doing a lot of fettling

Not sure what your question means, just check there are no leaks when filling and also when it warms up and gets to pressure.

I got the rear heater matrix flushed... Much of it ended up on my face haha, and I was able to fit a little camping water filter onto the end of the hose, which was quite perfect.

I just read something on this forum about the radiator shutoff blind? What is this sorcery and where would I locate this to check to make sure it's not blocking flow to the radiator? Or does it even exist on my 1992 3L?

For me, with the 2.4 instead of the 2.8 (but same engine apart from size), the visco fan is very noticeable. You can clearly hear it engaging, even on the highway. You can even notice a small difference in power, because the fan can take a few hp.

You might need to find out what solvent will dissolve the Bar's Leaks and put some of it through with a flush as you'll really need to be sure you've removed all of it from the system otherwise it will be 'the gift that keeps on giving'. I cringe at the thought, that stuff is horrible and I'd never consider using it on any recent vehicle.
I agree you won't miss when the viscous coupling cuts in, the change of sound and amount of air moving is very noticeable. Just have the seat up to access the engine and hold the throttle to bring up the revs a bit then watch the temp gauge and the fan as the engine warms up. On ours I can see the gauge rise then drop some when the thermostat opens, then rise again until the fan goes full power and it drops a bit again. Note that I have done the modification to remove the central 'dead zone' that the stock gauge has.
I keep forgetting about the rear heater as ours doesn't have one and I don't know if it ever did but yes that also needs flushing as you have done.

AgathaAlice wrote:

Note that I have done the modification to remove the central 'dead zone' that the stock gauge has.

Ah, I didn't know you'd done that! I think you still have the stock 1kz plumbing? Is there much variation in use of the gauge? Did you use my resistor values or find better ones to centre the gauge? Mine settles just above the middle but I have a landrover thermostat and different plumbing now so I'm not sure how that relates to the original state..

(yes - I changed two things at the same time LOL)

I used the values I found in one of the threads here and yes it does settle a little above centre as yours does. I'd try different values but it's such a PITA to get the instrument cluster in and out as there's so little length on the speedo cable and so little space to get a hand in behind to unclip or reconnect it so Carole has been told that it is staying the way it currently is unless it has to come out again for some other reason! The thermostat is new and genuine from Toyota.
The modification did make a huge difference to the gauge operation; I can easily see how an unmodified gauge could give a driver a false sense of safety and lead to damage.
All the plumbing is standard as much as I can see but sometime when it is on a hoist I must look and see if there are any signs of pipework that once would have fed a rear heater and if so what has been done with it. I simply can't get under the vehicle when it isn't lifted and my driveway is not on the flat so I don't trust putting it up on just a jack.

Speaking of rear heaters, I can understand why someone would take one out. In flushing the rear heater matrix the other day I found that the hard part of the soft, hard, soft piping had a nice little pinhole in it. I decided to get 60 inches of housing, a bunch of new hose clamps and some hose unions and took out the disgusting rotten metal piping. Great advice to flush that rear matrix, every hose I replace now will help in the long term.

I'm going to try to get some pictures up soon for all of you to have a bit more context, but that's all for now.

Unbeknownst to me, my rear heater hard lines were rotten as well when I picked up the van. I think I'm lucky I was able to drive it home from the port without them rupturing! They got replaced with soft lines, and all the other soft lines were replaced at that time as there was a lot of rust scale in them. You could hear an audible crunch when you squeezed the upper radiator hose! :/ I've got a few more flushes to go before I'll feel 100% confident about the system, though it's operated without issue so far.

@Leeku13 if you have a look at the pictures of our van in the 'show us yours' thread you'll see that with all the custom work that was done back in Japan there's no sensible use for the rear heater so if it ever did have one it would have been removed back then as part of that work rather than as a result of problems, which is perhaps fortunate.

@djathens you had a lucky escape then!

@AgathaAlice Your van is amazing!

@djathens All the coolant lines in the engine bay for me are nice and supple, I don't have the time or money to replace them so that is really lucky for me, but the ones going to the rear heater matrix, as they're exposed more to the elements under the van and out of the skid plates, were definitely doing the rusty crunch when I took them off. It feels good knowing they are back in good shape.

I got a couple more flushes with a hose and a filter done yesterday and filled it with coolant to prepare for when the coolant outlet comes.

I did have one other question though, I want to find a viscous fan clutch online so that I can order it quick if it turns out that I need it, but I'm having trouble finding the part number on jp-carparts or toyodiy. It doesn't seem to be in the radiator section, and the belt section didn't prove to be much help either. I did find one on Australian eBay for the 3L Hilux with model number LN107, but would this transfer over to my LH107? It didn't list the parts number either, so no way to cross reference or search that number in toyodiy...

Again, thanks to everyone for the assistance, as a 25 year old with minimal wrenching experience and very little cash to throw at a mechanic, y'all are one of the best tools i have for figuring this out.