M35A2 Running Hot

[palskidoo]

Hello All,
Last week I pulled the Deuce out of her winter resting spot hoping to get some dirt for the yard. (I start and let her idle every few weeks throughout the winter but no driving)

I checked the oil, coolant, tire pressures ect. Everything looked good so we headed out. A couple miles down the road I noticed the temp gage was at 180, couple minutes later 200, then 220. By the time i pulled into a parking lot the gage was sitting on 240. I popped the hood and the engine was definitely hot (what I would guess operating temp would be) but it didn't smell like she was over heating.... yet.

I've been doing some reading on here and the common responses seem to be either the gage, wire or sending unit is bad but; these cases all had the gage suddenly "pegged" at 240. I watched my temp rise rather smoothly. So I am thinking it is either the water pump or tstat. I will be pulling the tstat out and boiling it in one of the wife's pans on the stove (shhh, dont tell) to see if its working correctly.

Does anyone have any other suggestions on what could be causing this issue? My coolant is topped off. Radiator appears to be clean but i could spray out the fins.

Also, if I were to double check the engine temperature with an IR temp gun where the best spot? Anywhere on the block?

Thanks

 

[glcaines]

Use your IR gun where the temperature sending unit is located. If you are going to pull the thermostat to test it, I would go ahead and replace it with a new one. Just because looking into the radiator tank looks clean doesn't mean your radiator core isn't plugged up. Another possibility is the water pump. Make certain the belt is tight and not slipping. Also, the pump impeller can be bad. You're starting right though. Confirm you actually have an overheating problem with the IR gun.

 

[cattlerepairman]

I am not advocating to go overboard for what might be a simple problem. If you happen to be draining a lot of coolant in the process of doing thermostat and water pump, it might be good to flush the whole cooling system. Crud, rust and stuff are likely to accumulate over time, reducing cooling performance.

 

[palskidoo]

UPDATE!!
Yesterday I was able work on the truck and remove the thermostat. The first thing I noticed was how little coolant came out of the radiator and tstat housing. This is really odd because I checked the radiator the day she ran really hot. There was fluid in the radiator filler neck just below the overflow tube. So I would think that if fluid is visible in the fill neck the radiator is full.... no?

I am thinking that there may have been an "air bubble" in the coolant system which gave me a false sense of a full radiator.

Anyways, tested the tstat in boiling water and worked just fine. It began to open at 160F. I tried to purchase a replacement tstat at NAPA but i was told that THM 358180 is obsolete. So I was forced to get some gasket material and put the old tstat back in the truck. After I refilled the coolant, making sure she was as full as possible (adding water right into the tstat housing) I took her for a HARD run around town. The temp gage never went above 180F.
-----------------------------
On a different thought, does anyone else have an issue with coolant disappearing? I seem to always need to add a little coolant. There is no coolant in the oil! i checked because i was worried i had a leaking problem either with head gasket or the block somewhere.
Im trying to figure out where the coolant may be going.

 

[cattlerepairman]

Trucks have different preferences for where their coolant level sits when full. Sounds odd but is true.

If I fill mine to the filler neck, she will puke coolant until the level sits where she likes it. This is usually just below the filler. I can barely touch coolant with my finger when she is full. I can see it when I look straight down into the filler. And zero issues.

I suspect your truck also has a preferred level for its coolant.


Sent from my SM-G950W using Tapatalk

 

[M37M35]

I tried to purchase a replacement tstat at NAPA but i was told that THM 358180 is obsolete. So I was forced to get some gasket material and put the old tstat back in the truck.

The replacement T-stat is Stant 13938. I think Gates 33398 is also the correct one.
The T-state seal that goes inside the housing is Gates 33602.

Trucks have different preferences for where their coolant level sits when full. Sounds odd but is true.

Yup! I've noticed this too. Not so much on newer vehicles, but definitely on older ones.


Adding an overflow tank to the radiator might be a good addition. I did that on mine. Link.

 

[palskidoo]

The replacement T-stat is Stant 13938. I think Gates 33398 is also the correct one.
The T-state seal that goes inside the housing is Gates 33602.

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Yup! I've noticed this too. Not so much on newer vehicles, but definitely on older ones.


Adding an overflow tank to the radiator might be a good addition. I did that on mine. Link.

THANK YOU!!! I was just getting ready to start cross referencing part numbers for thermostats!

By the way, VERY JEALOUS of your center mount crane!!!!