I was wondering if I have a problem with the thermostat in my 95 Cummins it seems to slowly creep up to 190 or so then plumets down to 150 it does this rather quickly as I drive under all load conditions.Is this normal or should the t-stat be replaced?

 

Cummins says,

THE COOLING SYSTEM USED ON THE CUMMINS DIESEL ENGINE EQUIPPED VEHICLES PROVIDES THE CAPACITY AND PROTECTION OF THE HIGHER GVWR AND GCWR RATINGS AVAILABLE ON THESE VEHICLES. OWNERS SHOULD BE ADVISED OF THE NORMAL SLOWER WARM UP AND LOWER ENGINE OPERATING TEMPERATURES ASSOCIATED WITH DIESEL ENGINES.

THE COOLANT TEMPERATURE GAUGE WILL FLUCTUATE ON DIESEL ENGINE EQUIPPED VEHICLES. IT IS INFLUENCED BY VEHICLE LOAD, OUTSIDE AMBIENT TEMPERATURE AND EXTENDED IDLE TIME. THIS FUNCTION IS CONSIDERED NORMAL

 

So Bill I take it that this is normal?The reason I ask is I have to open up the cooling system anyway and figured I change it while I was in there but if this is normal why spend the money.....

 

its normal...i have it too...it fluctuates as well...even if im driving on flat road empty without wind....but it fluctuates slowly and regularly

 

Ok then I won't worry to much about it.I just want to be sure to get enough heat out of this system to keep my vegi oil hot enough.Does anyone know what temp. the stock thermostat is?

 

I just read your post after I posted a new one similar to your question. Did you replace your thermostat? I have a long trip ahead of me and I never noticed the temp gauge work so hard.........95 Dodge 4X4 Turbo 3/4 Ton.

 

Nope never changed it and I use the Ac every day and I have no problems,But to be honest I would like to run a hotter stat that didn't roam all over the place if there was one available?

 

Thermostats are cheap and after reading about one member losing two engines because of a faulty t-stat, I'd go ahead and replace it. My temps sit at 190* no matter what. Make sure you go to dodge or cummins and get one from them. Do not get the o'reilly brand or whatever cause those are junk and will bounce all over the place and not open soon enough. The one from the dealer is pricey at about $50 but it's well worth it in my opinion.

 

Blue, your temps are steady because you have a 24 valve, the fluctuations are 12 valve thing.
If you replace the stat on a 12 valve for one that doesn't fluctuate your temps will run colder.

 

Thanks for that info Infidal,I will need to keep the temps as high as I can to keep my vegi tank good and hot.So in your opinion my stat is fine?

 

I think so. Many of the folks who have switched to the nonfluctuating stats have switched back to get their temps back up.
I personally wonder how much the temp really does fluctuate. When I had an oil temp gauge it didn't fluctuate at all when the coolant gauge did. Leads me to believe that the engine temp is actually very steady.