Thermostat question
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Laughing Gas
Joined: Jan 2023
Posts: 1,172
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Thermostat question
I have a 88 f150 302. It’s been 85-90+ out lately and I think I ruined my thermostat I put in 2 years ago but just wanted to make sure there’s no other things to check before I change it. I have a 192 degree thermostat in it, and it runs cool unless I’m stopped or going slow, and I was going on some dirt trails with friends and it hit 220 then, and in the drive through it hit 225. And the reason I say it hit those is I think it’s stuck open from hitting that high. It takes forever to warm up which is out of character for it in this heat, and it sits around 160 till I’ve been driving for 10 minutes or so. But it went back to normal yesterday, and then when it hit 225 in the drive through it acted up again.
I’m probably gonna change the thermostat, but also should I go with a fail safe thermostat or a regular? It’s a $10 difference.
(I do have an aftermarket coolant gauge on it that is reading this and the cluster lines up with that)
I’m probably gonna change the thermostat, but also should I go with a fail safe thermostat or a regular? It’s a $10 difference.
(I do have an aftermarket coolant gauge on it that is reading this and the cluster lines up with that)
SPONSOR
Joined: Jan 2025
Posts: 496
Likes: 302
From: White Bear Lake
It's definitely possible it failed. With low speed and idle overheat I would suspect the fan clutch has failed and the fan isn't engaging to get enough airflow through the rad. I personally wouldn't go with the failsafe because if it gets hot once it's fully stuck open permanently. I would start with a good coolant flush and spray out the radiator and ac condenser fins to make sure you don't have a blocked up rad. Then see once it gets warmed up if the fan is moving some air. You should hear the fan when you rev the engine up. If you can get the temps over the 210-220 range shut the engine off and see how much resistance the fan clutch has. At that temp it should be pretty stiff. If it just free spins I would look into slapping a new fan clutch into it.
-Dan F
-Dan F
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Laughing Gas
Joined: Jan 2023
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I’ll check the clutch again. But I replaced it with a Hayden cause of this. And I had a new water pump radiator and hoses so I just gave up and kept an eye on it. But I’ll buy a regular thermostat and check the fins are fine
Cargo Master
Joined: Mar 2007
Posts: 2,793
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I have heard that once the thermostat has been overheated, the wax fails and the thermostat is junk. How true is that? Well, for the cost of the thermostat and assuming the bolts are not seized, it's worth replacing.
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Laughing Gas
Joined: Jan 2023
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That’s what I’ve heard to. But I just checked the radiator while it’s just been started, for the second time and still no flow so I don’t think my thermostat is stuck open but it’s still not reaching temperature
Unless you just can’t see flow?
I’m just gonna replace the thermostat anyway but figured I’d check other stuff to in the meantime
Unless you just can’t see flow?
I’m just gonna replace the thermostat anyway but figured I’d check other stuff to in the meantime
Cargo Master
Joined: Mar 2007
Posts: 2,793
Likes: 1,009
I learned a long time ago.....testing thermostats is a waste of time. They are just too cheap to buy a GOOD new one. One of the few things I do not test and just fire the shotgun.
Make certain there is coolant in the engine or they have a tendency not to open when they should.
Make certain there is coolant in the engine or they have a tendency not to open when they should.
Hotshot
Joined: Jul 2020
Posts: 10,354
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From: Near Salt Lake City
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Tuned
Joined: Jan 2007
Posts: 334
Likes: 100
From: Salkum
I always look for thermostats that have the little jigger pin air vent hole. Or if I can’t get one, I’ll drill a little 1/32 hole in the thermostat to vent any trapped air in the system.
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jiggle pin* yes good idea.
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