Engine/Transmission (1994 - 1998) Thermostat ?

[McCRam]

My temp gauge is fluctuating from 190 down to about 150. It doesn't matter if it is city driving or on the highway. I was ready to put a new tstat in, but I did a search and found that this has been a common problem. Does Cummins have a better tstat to replace this with? If so, can someone please give me the part# so that I don't have to do this twice. Even if this is "normal", I still want to stop it. It just ain't right.

 

[Howard Durand]

I don't see any information as to where you are or what truck you are driving but. if the drop from 190 to 150 is accompanied by the fan running, it should not be a problem, just normal operation.

 

[Joe G.]

It's normal. If mine didn't do it I would be looking for the reason why not. There is a lot of coolant in the system. So it takes a while to warm up enough to open the t-stat. Then cooler coolant flows into the engine from the radiator. There are t-stats that will smooth this fluxuation out. However, the only way I can think of that would do that is to restrict the flow of coolant from the radiator. That is NOT something that I would want on a hot day towing up a steep grade.

 

[bmoeller]

It's normal. It is worse in the winter than the summer. The only time mine is steady, is when towing or running 70-75 empty on a warm day on the interstate.



The sensor is in the head on the driver-side above and slightly to the rear of the fuel filter.

 

[JJW_ND]

Revised thermostat fixes this..

The revised thermostat that has been out for several years will stop the cycling but it does run slightly cooler. One needs to make sure all the air gets out of the system and the jiggle valve works and is not blocked or stuck.



While the cycling is very common I am not sure I would call it normal.



THe cycling is even worse in cooler climates. Even the new stat cycles once or twice but then stabilizes. Something the factory or several replacements (same as factory) never did.



jjw

 

[y-knot]

I am not so sure about it being normal. I had a thermostat that did the same, but randomly. It would stick and the temp would go up, then unstick and it would drop. Gust keep cycling, I got a new one from the Cummins dealer and it fixed it. Good luck.

 

[McCRam]

Sorry, I should have told you the specs. 97 2500 12v 5sp. And I live in MT. Its been in the low to mid 40's this week, it didn't seem to slow down the fluctuations much, and I have only had the truck for two weeks. I understand the cooling system is the same as the v10 trucks, so that the cummins would be overcooled a bit. Although, I have never seen fluctuations like this on a properly working cooling system before. My uncles 98 24v does not fluctuate at all, nor does our 91 D250 12v. Is it just certain years? From the posts on this thread and others I found, it seems like some trucks have been fixed. Is it just a better thermostat? I'm just trying to understand my new truck. I don't want fix something thats not broke. On the the other hand, I don't like my truck breaking down with a load of cattle in the trailer either. Thanks for the replies, and any further clarification would be appreciated.

 

[Andy Morrison]

it's not broken. it's normal !!!







Andy

 

[Slow Six]

When I had my 94 I installed a super stat from Napa. I also put in a 195 degree stat and ran it year around, heavy towing and everything. The stat would cycle up an down once or twice and then stablize. I was quite satisfied with this setup especially in winter. I ran with this for thousands of miles with no problems.

 

[mainer]

My '96 does the same thing - with great predictability.

 

[McCRam]

Thanks guys I appreciate the replies.