Bad Thermostat?

[Kyle Keller]

What is the normal temp range for a full warmed up ST? Once its all the way warmed up it runs between 198-207 farenheit. Also is the coolant from the overflow resovior supposed to cycle through while driving? I filled it up and then drove 30 miles with A/C on and the temp hovered around 200. But when i popped the hood afterwards the coolant in the overflow had not moved and the radiator hoses didn't feel full at all as if water was going through them. Am I just worrying about nothing or do I have a bad thermostat that needs to be replaced? Also I don't know if this matters as well but usually my overflow resovoir has to be topped off once every two weeks. Like it has a leak or something. Let me know what y'all think or if I'm just worrying about nothing?



Thanks

Kyle

 

[Gavin Allan]

You have a bad radiator cap.

 

[Mrlunchbox]

What makes you think its a bad cap? Just curious...

 

[EddieS'04]

Back during the summer I had to replace my '04 oem t-stat. I had noticed my temps on my scan gauge started creeping above 190/197, my summer norm. Gen 1 has a 192 t-stat, + or - 3 for error. It got to the point I was running 217 on the highway.

I used my digit temp gauge in a pot of boiling water, 212. OEM stat was only open about a 1/4".



Radiator cap is only to relief pressure from excess temp. Or normal expansion.



I would look at the t-stat.

 

[Kyle Keller]

But its never gone over 207. I drove for 30 minutes with A/C on in 70 degree weather. It stayed at 198-200 the whole drive. It never cycled from The overflow resovoir but if the tstat was stuck wouldnt that cause the temp to shoot through the roof? I'm thinking what Gavin thought that it could be losing pressure through the cap. If it helps diagnose it sometimes smells like coolant after the car is turned off.

 

[EddieS'04]

sometimes smells like coolant after the car is turned off

Pin hole leak somewhere. Are you having to add coolant?



The coolant will only cyle in the overflow. On expansion. With enough temp the pressure will go above the cap 16psi. Dumping coolant into the overflow. Then after cooling completely down. Upon cool down constriction. A vacuum is created pulling the coolant back down to the norm level.



Only fill the overflow to the cold level when cold. When you know the radiator is full when cold.



Maybe not understanding what you are asking.

 

[Kyle Keller]

I've had to add coolant a few times over the past few weeks. I'm not one to neglect a car just haven't had time till now to look at the situation. Basically the coolant from the reservoir is not cycling through. How do I know this? Because I added a slightly different color from a radiator leak preventive to the expansion tank and after 30 minutes/30 miles it was still the exact same color at the exact same spot in the expansion reservoir. The car stayed between 198-200 at most of the time but it did get as hot at 207. My question is....If it is the thermostat stuck or not operating correctly, after 30minutes/30 miles of driving, surely the temperature would have gone way over 200. Maybe 217 like you mentioned. But it hasn't. This is what is baffling me. If the coolant isn't cycling through from the expansion tank but the engine is not overheating what could be the cause?

 

[Kyle Keller]

As well as when the car is turned off you can smell a faint coolant smell.

 

[EddieS'04]

As well as when the car is turned off you can smell a faint coolant smell.

I suspect a pin hole leak, maybe. This leak is causing the preasure relief. So the cap is not having to relieving to the bottle.

Therefore you say you are having to add fluid.

I would look around the lower t-stat housing. Common leak point on the 4.0L motors. Also look at the radiator real close. For signs of seepage. you may have to take the fan shroud loose. To get a good look. Not always but, alluminum radiators. Tend to develop leaks at the bottom. Or the seals on the tanks.

Odd enough my neighbors trac. Had a hair line crack on the radiator nipple. Where the top hose went.

 

[swshawaii]

Ditto Eddie on the lower thermostat housing splitting and leaking.

Seems to be a weekly occurrence on here and other forums.

 

[Kyle Keller]

Replaced the thermostat and radiator cap this morning. Truck isn't running over 190 degrees. I'll check for leaks over the next few days. Thanks for all the help fellas

 

[James Williams]

Ya im having the same problem putting almost a whole gallon of water in the radiator every other day but its leaking some where so judging from what you guys have been saying i need to replace the lower thermostat housing .

 

[Gavin Allan]

If the engine is running at normal temperature and isn't overheating, it sure ain't the thermostat. Thermostat either works or it doesnt. It either fails open or closed. Your symptoms do not match thermostat failure.



If the cap's fails to seal to atmosphere then it won't draw coolant back when the eingine cools. The cap has to seel two directions: 1. atmosphere and 2. radiator pressure relief.



I would still replace the cap. Clean the neck of the radiator good before installing the new one. You want it to seal well.

 

[EddieS'04]

Thermostat either works or it doesnt. It either fails open or closed.

Gavin,

I have to disagree. Recently this past summer. My temps were reaching 217 on the highway.

It was my t-stat, only opening partialy. I tested it against a new one in boiling water. The new one opened completely as marked, 192. I also bought and tested 180 that is the one I used. The old one(marked 192) was bairly cracked open at 212 degrees. Maybe 1/8". I was using a new digital pocket stick thermomter. I also tested it against my old anolog thermometer. Of course I didnt need to. Water boils at 212 here.



I have had this to happen twice in the past. On other cars. I have got in the habit of testing new t-stats before install. Ever since I got a bad new one, years ago. It is a comfort zone for me. To know the exact temp the new one is wide open....