Need help! Gas engine overheating. Cannot resolve.

If you can find someone with a Techstream/TIS subscription, TIS has all the little flow charts to go through with the temp and voltage readings and sensor status, that can lead you to the strange stuff like some electrical connection issue triggering some actuator to stick. If you do throw in the towel and call a dealer, ask if they have on staff and if you can meet directly with a "Toyota Master Diagnostic Tech". If you have a nearby community college that runs a Toyota T-Ten program, even call and ask for an instructor and tell him your issue and ask who he knows who in your area can help (some of those guys like unique challenges and even do side jobs!).

 

Then cut the jiggle pin from the thermostat.

 

I've got to give it to Sergey, the most persistent guy ever!

Being down in Phoenix area, overheating is not at all rare. I've had a number of cars in my garage or driveway over the years with my DIY efforts relating to overheating issues. I'm no expert on physics but pressurized coolant seems to be key to removing enough heat. If pressure does not get up to spec the engine won't cool right under high loads.

Also aftermarket cooling systems parts are a problem,. I've learned the hard way to always buy the overpriced oem. Which it sounds like you've done.

I've had aftermarket thermostats operate at wrong temps and lead to all sorts of trouble shooting until replaced again with OEM.

Caps are really important. I've had OEM caps fail, but I've had overheated engines with aftermarket caps. 96 prizm, 99 Volvo most recently.

One of my sons engine swapped his MR2 with one of those super duper drift car Japan engines. It overheated constantly, it passed pressure tests, and the cap passed it's pressure test. He bought a bigger radiator, a bunch of caps, then We stumbled onto a theory that a tiny little nub inside the cap housing (not part of radiator on that car) was causing an issue. Filed it off and solved.

I had an old 66 mustang that overheated in summer only going up hills or sitting in traffic. It used only a couple ounces of coolant per month. And oil was never cloudy so didn't suspect head gasket. Drove it like this for 3 years, later had a pushrod bend and took the heads off, hairline micro crack found by the machine shop was causing pressure issues and overheating. New head on one side fixed it.

I'm not sure any of these are even related to your issue, but who knows sometimes one idea leads to another. Best of luck.

 

Update: I have taken it to the dealership, but they refuse to diagnose it beyond simply replacing parts at $500 a piece (water pump, thermostat, etc.). All of this I have already replaced with brand new OEM parts directly from the dealership. In fact, I just replaced the water pump for the third time today.

Several days ago I blocked off the heater exchange (near the catalytic converter). I basically took the two hoses, put an L-shaped brass connector from Lowes between them (red circle in image below), and then blocked off the two ports on the cat side with a standard rubber cap (orange circle in image below).



Refilled coolant (with sensor above EGR taken out, to allow air to escape), and burping air with car at an upward slant. During this process, the car backfired once. I assumed it had to do with the modification, and the computer recalibrating. Afterwards, I took the car for a test drive and it was worse than ever. Temps rose to 245°F within 3000 feet - I limped home slowly. This time I even had steam billowing out from underneath the car and out of the hood (from the general area where these modifications had been made). I recall reading a thread where someone did this same mod., and had steam for the first test drive, but it cleared up (from coolant in heat exchange burning off). It doesn't answer why the temps rose higher than before. I'm kind of at a standstill. Dealership isn't particularly helpful, and I'm not sure a non-dealer mechanic would even be able to dig me out of the hole at this point. I'm to the point of selling it to a dealership and being rid of it - maybe get $500 for it.

Why I blocked off heat exchange: I was under the impression that coolant circulates through the heat exchange for the sole purpose of heating up coolant in winter months, and that there is a valve which shuts off coolant flow once the temp has risen to a certain point. It is possible for this valve to lock open and cause catalytic converter to constantly boil the coolant, causing overheating. This was the theory. But I'm still in car hell.

I still haven't tried modifying thermostat as Ragingfit suggested - that is likely my next step. I guess my question is, should I consider undoing the heat exchange modification? Should I associate this with the worse-than-usual overheating?

 

Hi Jacob, It seems like the Mod did not work so (one vote) that it may make sense to reverse it. Do you know anyone that has access to TechStream? It connects in a way that provides way more info then a OBD reader--you can get things like rpm readings on the water pump which is determined by a reading on another sensor along with all the other settings and sensor readings to the cooling system. If not have you been able to test for trace amounts of exhaust gases /hydrocarbons in the coolant? If the car is in decent shape other then this problem don't get frustrated and give it away for $500, A Prius with a blown motor is worth at least $1500-$2000 more IMHO.

 

Update: I removed the thermostat from the thermostat housing as @Ragingfit has suggested and that did the trick. Drove over an hour and the temps never reached above 170 (F), mostly staying around 140. I am thinking this will come with it's own problems, so I will reverse the heat exchange bypass, and maybe (1) look for another thermostat), or (2) drill holes in the metal "barrier" of the thermostat to allow a small amount of coolant to constantly pass through it (as has been suggested earlier).

I just can't understand how I've replaced the thermostat three times (all from Toyota dealerships) and none of them have worked correctly... does anyone have a suggestion on a decent thermostat?

 

Yeah without a thermostat you're cooling is going to be constant. Protracted freeway driving in cool weather (for example), you might cool the engine too much.

When you get a thermostat, for giggles: suspend in a pot of water (not touching bottom), and bring to a boil while watching for it to open, and when. A thermometer in the pot (again not touching the bottom), will give you more feedback as to the temp it opens at. Suspend the original in there too, for comparison.

 

Is the thermostat fool proof meaning you can't insert it the wrong way?

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Boiled the OEM Toyota thermostat and it didn't open until 205-210 (F). It closed at 185-190 (F). My understanding (correct me if I'm wrong) is that it should be opening up by 185-190 (F). I've tried the AISIN off of Amazon with similar results (and by that, I mean bad results), so I guess I'll go with the DORMAN brand, and see if that fixes my problem...

I reversed my modification of the heat exchanger, allowing coolant flow once again. That brought up average operating temps to 165-170 (F), with upmost of 180 when getting up to speed on highway. Still, with the thermostat removed, that's a little on the cool side. Will update when my Dorman thermostat arrives.

 

Probably better to research elsewhere then condemn the OE Toyota thermostat of which you've tried 3...

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Perhaps you aren't installing it correctly? The little bleeder hold with a piece of metal in it goes up.
If it doesn't have one, drill a small hole in it, and it goes up....

 

Technically, the first one I tried was the one that arrived with the 4th gen engine which I put in my 3rd gen car. The second one I tried was an AISIN from Amazon. The third was an OEM one from Toyota. At least I think.. it's getting hard to remember at this point (I've been working on this thing for 2 years)

 

@Jacob Bonner Okay. Now I'm getting my bearings. This is an engine overheat thread. People are coming in with plain Jane overheating BUT yours is a Gen 4 to Gen 3 engine swap overheating. I've seen people get this done at shops, and drive off happy campers, so we just don't know the secret!

As I understand Toyota made improvements to the Gen 4 engine to improve efficiency. The question is how? How can one improve efficiency? I would guess the #1 way is to run hotter. So you have a Gen 3 ECU managing an engine that's trying to run hotter than the ECU wants to accept.

Possible solutions:

You actually asked this back in 2020, replace Gen 3 ECU with Gen 4 ECU and let it run hotter.

Install a Gen 3 thermostat and cross your fingers. (Is this possible? I mean are they the same except for temperature at which they open)? I guess is keep everything as much as possible Gen 3 except those that must be Gen 4 (ie ONLY Gen 4 part fits).

I'm beginning to suspect it is not air in the system. Can verify by researching Gen 4 bleeding procedure.


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so now this thread is a gen 4 engine overheating? Now Im starting to understand how what people with a.d.h.d. goes through.

 

I've considered the type of coolant may cause the overheating because of it's surface tension or viscosity.
If the jiggle pin is sized for Toyota coolant and I'm using Prestone (Propylene vs Ethylene or HOAT vs OAT, whatever) it may not be able to bleed the air through.
This is a wild guess and should not be taken too seriously but who knows.
It is obvious, air gets trapped behind the thermostat and insulates it, causing the thermostat to stay closed.
Cut the jiggle pin!

 

PIN! Thanks! I could not remember that name!
And make sure you are using the correct coolant...

 

After reading this from (EDIT post #184):

"Update: I have taken it to the dealership, but they refuse to diagnose it beyond simply replacing parts at $500 a piece (water pump, thermostat, etc.). All of this I have already replaced with brand new OEM parts directly from the dealership. In fact, I just replaced the water pump for the third time today."

I went back to his first post in this thread, (he's not the OP), and read through as much as I could bear then started skimming. Yup, Gen 4 engine swapped into a Gen 3.

Maybe bring the car to one of the shops that do these engine swaps for repair...

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and post in gen 4 sub forum since gen 4 cars have gen 4 engines with gen 4 members there to help.

 

Now you are just being racist!!!!!!!