12v Cooling Issue

[Jared Mason]

I'm new to the diesel world, so I apologize for my lack of knowledge. I just purchased a 96 Ram 2500 12v and it has 66,000 miles on the truck. I had someone flush the coolant and change the hoses. While doing so, they put in a NAPA Safety Stat Thermostat in it. The new thermostat behaved differently in that it, if the engine cooled down for a few hours, would go above 190 degrees to I'm guessing around 200 degrees because the temp gauge isn't numbered for 200. Once it reaches the 200 degree mark on the temp gauge it falls back down to about 150 degrees and cycles between 150 and 190 degrees for the remainder of the time.

So I put an Orielly's Thermostat (180 degree) in Friday night. It's seems to behave roughly the same way.
I have a Coolant filling funnel that allows me to 'burp' the coolant system. I got it to burp. I'm not sure if more air is trapped or not.

I've got a Cummins thermostat on order.

Is this normal temp behavior for one of these engines? I expect the cycling. But not high temp on the warm up.

Thanks for any help or advice.

 

[Cummins12V98]

YUP. USE a QUALITY T stat.

 

[Timd32]

Sounds normal for those stats. Maybe they are just opening a little later. Swings are normal as you noted.

Swap the Cummins in and it is what it is. I have a Gates from Geno's I'm pretty sure it does about the same thing. Little over 180-190 and back down.

I did not need to use a special funnel set up on my truck, I have flushed and filled mine a few times. Not that I would expect that to cause any issues, just I did not need to do that.

You can always throw them in a pot of water and watch them operate.

 

[GAmes]

The temp swing is normal. https://www.cumminsforum.com/forum/94-98-engine/449279-low-fluctuating-coolant-temperature.html

I suggest you acquire a factory service manual. There is no need to "burp" a 12 valve's cooling system, a couple of normal heat cycles will purge all the air. A small excerpt from the manual.

"The air bleeds (jiggle pins) that were used on the thermostats of diesel engines in previous years are
no longer used. They have been replaced by a vertically mounted one-way check valve (jiggle pin) and a
rubber bypass hose. The check valve is used as a servicing feature and will vent air when the system is being filled. It is also used to block the flow of coolant during engine operation (all coolant will pass through the thermostat.)"

A FSM will be the most used tool in your shop and pay for itself very quickly. I prefer the print version.

https://www.genosgarage.com/product/dfsm96-print/dodgeram-factory-service-manuals
https://www.genosgarage.com/product/dfsm96-cd/dodgeram-factory-service-manuals

 

[Joe Mc]

Welcome to the world of Diesel and the TDR! Odd but proven (there are many threads here on Cummins vs over the counter parts) the Cummins T-stat and water pump work best. I too tried to save a few bucks and purchased new T-stats and new (not reman) water pumps over the years only to have them fail, EXAMPLES: 1.) 2 new (not reman) water pumps lasted 1 year each (replaced under warranty and ultimately credited full amount when I returned) - purchased new from Cummins, going on 5 years now. 2.) T-stats just didn't seem to function as the original one, Cummins stat rock solid at 190 (this time of year) it'll fluctuate some in the summer with the A/C on but not much. Don't get sticker shock when you see the price difference between Cummins and over the counter parts, just remember you get what you pay for and is your engine worth the possibility of damage due to inferior cheap parts? Answer = "NO".

 

[The patriot]

Yes, to all stated above.
Also, I read somewhere (probably here) that the early 2nd gens had a faster gauge than say a 1998.
They were getting complaints, so they dampened the 1998's and newer so the swing isn't so noticeable.

 

[Timd32]

Yes, to all stated above.
Also, I read somewhere (probably here) that the early 2nd gens had a faster gauge than say a 1998.
They were getting complaints, so they dampened the 1998's and newer so the swing isn't so noticeable.

Was probably a very minor subset of complaints that they listened too. I'm amazed how much Cummins had figured out with these 5.9's. Now its all a joke, in my 4th gen gasser, you should see how fast the made up numbers change, I will have to video it, all the numbers are made up. Which is fine as long as you dont get caught up that they might mean something.

 

[Matt42]

Be wary of the drawing used in the 1996 factory service manual that shows the orientation of the t-stat! It shows the rubber gasket and t-stat being put in backward. Aftermarket repair manuals picked up the drawing and repeated it. It's easier to put the t-stat and gasket in right than wrong, despite what the drawing shows.

Also, the disquieting temperature gauge swings are perfectly normal. The actual operating temperatures inside the engine are going to be OK.

Even so, buy a copy of the factory service manual from Geno's. I bought one right after I bought my truck--23 years ago. It was worth every penny, despite the picture.