Thermostat stuck open, backordered

Wredge · Mar 1, 2022

Hi:
Sorry. This is a long post.

I estimate that I drove at least 1000 km (600 miles) with the thermostat stuck open, maybe even double that. The last two gas fill-up I noticed the range to empty was 500 km instead if the usual 600 km range. At first I assumed low air, then the tire type. When I questioned the low cabin heat and then saw the gauge needle either just below or just above the cold mark, that’s when it hit me that the thermostat was stuck open. Toyota’s diagnostic confirmed it and only then told me that it will be six or more weeks before I might get my new assembly from Toyota Service Dept (I’m third in the list and they don’t know how many they will receive.

I read here that the system compensates for the lack of heat with a richer gas mixture, which in the long term, can damage the catalytic converter and maybe the engine; so, I parked it.

I found and just ordered the housing on Ebay (might get it in 4 weeks) and ordered a thermostat from Rock Auto. I didn’t find a seal for the housing yet.

So now I’m wondering if I might have actually caused some damage by driving it as much as I did during the coldest Canadian months of the year.

Also looking for comments and advice on my idea of assembling the housing. Toyota says I could crack the housing.

And I’d like to know if, by putting a piece of cardboard and carefully watching that the temperature gauge goes up to but not over half, (like in the old days) I could prevent further damage while allow me to drive it, or is there something else that is affected by the open thermostat (maybe related to the sensor on the housing) that could still be an issue.

Any help will be greatly appreciated.

BMR · Mar 2, 2022

It would be running with “default” fueling curves, which are intentionally rich to avoid engine damage. This can cause cats to overheat to the point the honeycomb core melts down and blocks the flow of exhaust gases. I’ve got a ‘97 F150 that did this. But I’ve not heard of it being such a problem on Toyotas, so they must not set the defaults so rich.

Wredge · Mar 3, 2022

First, thanks BMR for your comments; that helps to learn that enriching the fuel actually protects the engine. I assume small trips to groceries, etc… may not be too harmful. Btw, same thing happened to the cat on my ‘81 T-Bird.
I’m still considering retricting air flow to the rad if this can help the exhaust system overall; otherwise, and to avoid any overheating risks, I can tolerate colder cabin temperatures. The coldest days are behind us anyway.

And, if I receive my used OEM housing and new OEM thermostat before the back-ordered new assembly arrives, and manage not to crack the housing while assembling them, I’ll replace the assembly. Got the gasket too.

Has anyone gone through replacing the thermostat? Any suggestions like heating the plastic housing, lubes or whatever?

Thanks!

drcoffee · Mar 4, 2022

I had to do it on my 2008 and 2014. Its not a bad job. Drain the coolant, then using a 10mm socket on a 1/4” ratchet with a 6” extension. A wobble would be handy as there is no straight line to the nuts. Plan for spillage because the cross pipe that feeds the T-stat will still hold coolant when you pop it out. The quality of oem is so much better than anything aftermarket. Buy OEM Toyota. No sealant is needed.
Might be a good time to replace the belt and idler pulleys while you are in there.

the housing is aluminum. You just need the thermostat and seal. The nuts get torqued to 9-10 ft Lbs (snugged down). Dont crank on it.

Wredge · Mar 28, 2022

Thanks to everyone who helped and has made me feel welcomed. Thanks Dr. Coffee for your detailed information.

Two weeks ago, I received from eBay, a brand new OEM Toyota housing assembly - complete with thermostat. Parts department confirmed it.

Since the oil change and air and cabin filters were due, I just got them to install the new housing assembly. They also found a rear shock leaking, which I replaced last Friday. I couldn’t, at this time, manage the belt and pulley job with the rest. Hopefully, at 82,000 Km (52,000 mi), I didn’t make a risky decision.

Btw the “OEM” thermostat from Rock Auto looked nothing like the one in the housing. Returning it.

So, thank-you all for your support.

Thermostat stuck open, backordered

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