Engine/Transmission (1994 - 1998) thermostat ??

[BigEasy]

This week, I made two round trips from home to Knoxville TN... a few times along the way, I noticed the temp gauge going up and down in the 150-190 range. The gauge is usually right around 150 all the time since I got the truck in September, but the heater blows hot and it's getting good fuel mileage, so I just figured maybe the sender was bad.



Any ideas?



Just a note... I love this truck! I averaged over 20 mpg with a 4x4 at 75+ going thru the hills of PA, WV, VA, and TN!!!

 

[ChillyDog]

My '97 does the same thing, as do most of the 2nd Gen 12 valves. It is very common and is not something to worry about.



Bill

 

[TRAMPLINEMAN]

My '97 does the same thing, as do most of the 2nd Gen 12 valves. It is very common and is not something to worry about.



Bill

What he said.

 

[BigEasy]

Thanks for the info... anyone know what causes it? I'd like to get the temps to stay at a steady 190... will these build enough heat to do that or not?

 

[EKlem]

For most people who are not pulling really heavy loads, the coolant in the radiator is much cooler than the coolant in the engine. The temp gauge will climb slightly when the thermostat is closed because it is only heating up the coolant in the engine. When it reaches the set temperature, the radiator is connected into the system and a whole lot of cold coolant is introduced which explains why the temperature will drop very quickly when it hits 190 or so. It scared the heck out of me too when I first saw it.



There are a couple of things that can help deal with it but it really isn't a problem. In cold weather, blocking parting of the grille can help so that the radiator doesn't get the coolant as cold. Another thing is that hooking a big heavy trailer to your truck will usually make the fluctuations less. The other thing that some people have had luck with is modifying their thermostat. The way it is designed, the coolant doesn't get good flow through it so it is slow to react. I remember someone posting a diagram of where they had drilled some extra holes in the thermostat and claimed that it was working better. Also, cummins came out with a redesigned one but I haven't heard whether it works or not. I wouldn't worry too much about it though.

 

[WDixon27]

i have the "updated" t-stat and the temp gauge was doing a impression of a windshield wiper, i drilled a couple small holes in the body of the t-stat so that the element wouldn't get shocked as badly by the temp changes, it helped a lot on unloaded running and next week ill find out loaded as i am going on a 2300 mile round trip towing about 6k for the 1st half and about 8k for the return trip

 

[MKline]

My '97 does the same thing, as do most of the 2nd Gen 12 valves. It is very common and is not something to worry about.



Bill

Mine has been doing it for 3 years, and never gotten over 190.

 

[Missouri Mule]

My has been doing since I've owned it. It has only gone over 190 once.

 

[TRAMPLINEMAN]

I also have the "upgraded" t-stat. I pull heavy loads all the time and it still does it. I haven't tried drilling yet, YET!

 

[MFrenchek]

I had to change out my thermostat as the engine wasn't even getting up to 150. Found the original stat had a rubber seal that broke and wedged in the opening. I got a NAPA hd unit and now it runs about 185 pretty consitently loaded or unloaded at all speeds and conditions. Can't recall the part number.

 

[Joe G.]

Mine went up and down for years. On a fishing trip to OR it stopped doing that so I was suspicious. The rubber gasket had slipped and jammed it open a little. I got a new one from NAPA. It's moving up and down again like it was so I'm comfortable with it again.

 

[MKline]

Mine went up and down for years. On a fishing trip to OR it stopped doing that so I was suspicious. The rubber gasket had slipped and jammed it open a little. I got a new one from NAPA. It's moving up and down again like it was so I'm comfortable with it again.

It's amazing how we are not happy unless we have all our quirks happening. :-laf

 

[Extreme1]

My truck overheated so I replaced mine on a trip and the fan clutch was actually the problem. The NAPA replacement doesn't fluxuate like the original one did. There were a bunch of write ups in TDR years ago, the fluxuations don't harm anything but because of all the comments by concerned owners (see above), they changed the T-stat to respond slower and it doesn't fluxuate. My new NAPA T-stat keeps the engine on the lower end of the temp guage now, I miss the old one (especially in the winter).

 

[Highfinance97]

Mine also has been doin it since i owned it, but now today... ... ...



i was racing a VW on the interstate today and my engine temp got a little above 190 probobly 205-210 so i decided to drive normal and it went back down to 190.

when i got off the interstate and started driving around town it stayed at 140-150 , i got to my destanation, shut it down, and left.

about an hour later got back on the highway and it stayed between 140-170



What is going on



Michael

 

[TRAMPLINEMAN]

Your rubber gasket might have slipped and is keeping it open a little. Just an idea.