Time to Replace the Thermostat in my FJ60?

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In the 18 months I have had the 60, it has never seemed to run particularly hot, but after a 60 mile drive on the freeway earlier this week the temp gauge barely rose a click above C. Today, I picked up a temp gun and ran a few hours worth of errands (freeway driving, in town driving, etc.) and after a good 20 min run on the freeway, here was the temp gauge in the cabin and then the readings from the engine bay with the engine still running.
Dash Gauge.jpg


Reading 1.jpg


Reading 3.jpg


Reading 4.jpg


Reading 5.jpg


Reading 6.jpg


Questions: do results like this warrant replacing the thermostat? any other diagnostic work I should do before deciding?

There is a bit on overcooled engines here, and I found this thread that leaned towards yes (Problem with Thermostat or super efficient cooling system? - https://forum.ih8mud.com/threads/problem-with-thermostat-or-super-efficient-cooling-system.778689/) but it is also from 2013, so I wanted to see what current thinking might be.

Thanks in advance for the input.

Reading 2.jpg
 

Godwin

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If you don't know the history of the thermostat and cooling system replace the t-stat. You may simply be missing the o-ring that sits on top of the t-stat, or it may be degraded. A new t-stat and o-ring will bring your temps up to normal.
 

Gretsch

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In the 18 months I have had the 60, it has never seemed to run particularly hot, but after a 60 mile drive on the freeway earlier this week the temp gauge barely rose a click above C. Today,

When I first got my 60, it would run this way all the time. Temp barely above C. I replaced my cooling system just as general maintenance and added a new thermostat as part of that work. It ran hotter than it had after that work so I thought something was wrong. The top gasket was missing on my thermostat when I got in there to replace it. Read here that missing that gasket could cause the temp to run low like that. After replacing it on mine it started to run in the normal temp range. Perhaps your top gasket has deteriorated and is now not allowing the cooling system to work properly and run the temps low like that. Would agree with the others. Crack open the housing and see what's going on. HTH.
 

g-man

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What Godwin said. Mine was running just like yours and when I took it apart I found the top gasket/o-ring had been misplaced during install and this lets coolant past it, keeping running temps below normal.

Here I outline my unorthodox method to install and test that the top gasket has not moved:

Maybe I'm just crazy but I put my t-stat on very differently than most. I unbolted the lower housing from the head. While the thermostat was still inside the housing I could look in and see the top gasket was dislodged. That top gasket can easily slip out of position during install. After cleaning up the mating surfaces, I put the thermostat housing assembly together on a bench. I turned the top of the housing upside down and put the top gasket in first, then put the thermostat in upside down making sure the gasket is centered and the thermostat is sitting flush on it. Next I coated with rtv the lower gasket on both sides and put it on the lower housing. I turned the lower housing upside down and carefully put it on the mated surface of the top housing. Then holding it all tightly flipped it over and installed and tightened the 4 bolts. Next holding my thumb over the oil cooler hose attachment I blew in the top hole to make sure that I had a seal and no air was getting by. Lastly I replaced the lower (housing to head) gasket and with some rtv, bolted back on the head. This can get a little tricky with other stuff in the way but is doable. Probably not the normal way but made sense to me to be able to check the top gasket.
I suppose you could air test the top hole in the housing by attaching several graduating smaller hoses together so you can test blow through it w/out removing the lower housing. I was working on replacing my head and it all had to come off anyway.
 

Godwin

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Good idea to have new OEM bolts on hand in case any break. This is the part no. 9161160845. Reinstall with anti-seize.
 
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How much of the bolt stub is exposed? Heating the lower housing with a torch will aid in loosening the broken
Is ju
What Godwin said. Mine was running just like yours and when I took it apart I found the top gasket/o-ring had been misplaced during install and this lets coolant past it, keeping running temps below normal.

Here I outline my unorthodox method to install and test that the top gasket has not moved:

Maybe I'm just crazy but I put my t-stat on very differently than most. I unbolted the lower housing from the head. While the thermostat was still inside the housing I could look in and see the top gasket was dislodged. That top gasket can easily slip out of position during install. After cleaning up the mating surfaces, I put the thermostat housing assembly together on a bench. I turned the top of the housing upside down and put the top gasket in first, then put the thermostat in upside down making sure the gasket is centered and the thermostat is sitting flush on it. Next I coated with rtv the lower gasket on both sides and put it on the lower housing. I turned the lower housing upside down and carefully put it on the mated surface of the top housing. Then holding it all tightly flipped it over and installed and tightened the 4 bolts. Next holding my thumb over the oil cooler hose attachment I blew in the top hole to make sure that I had a seal and no air was getting by. Lastly I replaced the lower (housing to head) gasket and with some rtv, bolted back on the head. This can get a little tricky with other stuff in the way but is doable. Probably not the normal way but made sense to me to be able to check the top gasket.
I suppose you could air test the top hole in the housing by attaching several graduating smaller hoses together so you can test blow through it w/out removing the lower housing. I was working on replacing my head and it all had to come off anyway
What Godwin said. Mine was running just like yours and when I took it apart I found the top gasket/o-ring had been misplaced during install and this lets coolant past it, keeping running temps below normal.

Here I outline my unorthodox method to install and test that the top gasket has not moved:

Maybe I'm just crazy but I put my t-stat on very differently than most. I unbolted the lower housing from the head. While the thermostat was still inside the housing I could look in and see the top gasket was dislodged. That top gasket can easily slip out of position during install. After cleaning up the mating surfaces, I put the thermostat housing assembly together on a bench. I turned the top of the housing upside down and put the top gasket in first, then put the thermostat in upside down making sure the gasket is centered and the thermostat is sitting flush on it. Next I coated with rtv the lower gasket on both sides and put it on the lower housing. I turned the lower housing upside down and carefully put it on the mated surface of the top housing. Then holding it all tightly flipped it over and installed and tightened the 4 bolts. Next holding my thumb over the oil cooler hose attachment I blew in the top hole to make sure that I had a seal and no air was getting by. Lastly I replaced the lower (housing to head) gasket and with some rtv, bolted back on the head. This can get a little tricky with other stuff in the way but is doable. Probably not the normal way but made sense to me to be able to check the top gasket.
I suppose you could air test the top hole in the housing by attaching several graduating smaller hoses together so you can test blow through it w/out removing the lower housing. I was working on replacing my head and it all had to come off anyway.
Is just the 2, 14mm bolts attaching the lower housing to the head?
 
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Well. Got to get my hands on some new bolts, but everything out and looks like the worn out o-ring that I had to fish out of the lower thermostat housing was the most likely culprit.

Thanks for the input so far folks.
9EE54566-F803-46E6-8074-1F75B33C808B.jpeg
 
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Predicting the future…now I have to teach myself to extract the broken bolt.View attachment 2888566
Haha, I’m in the middle of the same job and same exact thing happened to me. Of course I then broke the extractor trying to get the stub of a bolt out. I ended up carefully center-punching the stuffed hole and progressively drilling it out just short of the threads. When I got real close, I reamed the hole with a M8 tap. I got lucky and didn’t need to helicoil. Threads are only a little damaged. The tap (VERY well lubricated) did a nice job of chasing out the remaining bits of the bolt.
 
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Don’t cheap out on the thermostat.

F3982B91-6421-42C3-821C-D8F2002C352D.jpeg

Think these are 3 different thermostats? Wrong. They’re all supposedly for my 62. On the left, a Duralast I bought a while back as an emergency spare. Stamped “Motorad”. In the center, what I pulled out of the truck. At right, a new Aisin.

I’m assuming the center one is Aisin or some other Toyota OEM judging by how stout it looks. The sheet metal is thicker, it’s made from fewer pieces, and it even has a little tuning screw at the top. The new Aisin is close to that quality level, and the Duralast is just … garbage. It also does not fit snugly into the thermostat housing. It’s about 1mm shorter than the original or the Aisin.

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8100AD09-DB48-4AD7-BBC7-CACE4689F593.jpeg

The difference between a good one and a crappy on is only about $5, but you’d never know if you don’t compare.
 
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Don’t cheap out on the thermostat.

View attachment 2889303
Think these are 3 different thermostats? Wrong. They’re all supposedly for my 62. On the left, a Duralast I bought a while back as an emergency spare. Stamped “Motorad”. In the center, what I pulled out of the truck. At right, a new Aisin.

I’m assuming the center one is Aisin or some other Toyota OEM judging by how stout it looks. The sheet metal is thicker, it’s made from fewer pieces, and it even has a little tuning screw at the top. The new Aisin is close to that quality level, and the Duralast is just … garbage. It also does not fit snugly into the thermostat housing. It’s about 1mm shorter than the original or the Aisin.

View attachment 2889308



View attachment 2889309

View attachment 2889311
The difference between a good one and a crappy on is only about $5, but you’d never know if you don’t compare.

Excellent point. The difference between the thermostat from Napa (left) and what I removed (right) is pretty significant. Presumably the one on the left is 30 years newer, but definitely worried about fit now.

A61BF4E0-AD20-4F54-BF64-1C04B59C78EB.jpeg
 
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Been a long time since I regularly tried to work on my own vehicle (which was a 71 bug in high school), but thanks to all of the input here I was able to get this all sorted out.

Had to get the bolts from Toyota, so decided to go with the OEM thermostat after comparing the two.

Was pretty straightforward putting it all back together, and after 20 minutes of idling and a driving around the block a few times, no leaks, temp seems about right, and that heater had me rolling the window down.

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