Engine/Transmission (1994 - 1998) Water Temps all over the place

[jburnes]

Since new the water temp gauge has moved from 150 to 220 depending on my load and grade. I replaced the thermo and am still having the problem. 56k on this thing and change out the fleetguard 50/50 each spring (flush too). I know the fluxuating readings have been a problem so what's the fix?Dump the transmission cooler and add a remote cooler w/fan? Help!



1996 4X4,Auto rebuilt of course, Banks, Rip Rook Exaust 4" thanks Rip! 56K

 

[Matt42]

This is a normal condition. Mine does it, too. It's never been a problem.



The 1996 Owners Manual, page 57, states in pertinent part:



"NOTE: 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 fluctuation is considered normal.



"Gauge fluctuation will be noticeable most often when driving at steady highway speeds and stop and go city type driving. "



And by the way, welcome to the TDRoundtable.

 

[redram]

That's a bunch of bull. I have a 96 and I also had a 89. The 89 NEVER fluctuated except for a load factor.



My 96, with the cruise control set, running on flat road (everything around Houston is flat) with the air on or off, the water temp guage would "fluctuate" from 140 to 190 area on the dash guage in as little as 20 seconds to no more than 45 seconds and then would drop quickly down to the lower temp and repeat for hours on end.



I agree, where the guage would register will vary if it's 90 F out 32 F, whether towing or pulling a grade. But why did it vary so much in 45 seconds?



Because Dodge had a crappy thermostat setup in 96. I went to the upgraded thermostat several years back (search the archives for the most recent upgrade from Cummins) and also switched to the premixed Texaco Long Life Coolant (Dexcool) and my guage no longer fluctuates nor runs over 180 degrees even in Houston heat and humidity.



That line in the owner's manual and shop manual was the biggest CYA I've ever seen. I was concerned about running the engine too cold due to the thermostat opening and closing repeatedly, I didn't have a temperature guage, I had an open / close indicator for the thermostat!



It was as accurate / functional as my fuel guage isn't!!!!

 

[dan_gilson]

That thermo swing was the last straw for my '96. Dodge could not fix it. I called Cummins and at least they gave me a good explaination why and that they were working on it.



There is supposed to be a replacement thermostat that corrects this. It has more holes in it to let more coolant through when it is closed and a slower bi-metal to reducing opening/closing times.



You might want to use the search facility here and see if you can find a part number. I seem to remember a post a while back that had it.



I would not expect Dodge do know (even though they should). At least 2 Dodge dealer tried telling me that this was OK and not to worry. BullS^%$!!! At best you are reducing you fuel milage. I was more worried about thermo shocking that large mass of cast iron. A cracked block or head was not my idea of a good thing.

My 96 would go from 140 to 195 and back in 2 minutes when on the highway using the cruise control under light load. It was the only vehicle in 25 years to ever do this.

 

[Blakers]

It's normal for these engines. So why try to fix it when it doesn't hurt anything?



Blake

 

[dan_gilson]

I strongly disagree! It is a problem for this engine BUT NOT normal. Thermo shocking a large chunk of cast iron just can not be good. Cast iron tends to develope cracks when with cooled too quickly. Cycling temperatures quickly tends to cause problems with expansion across a lot of components.



I am not very good with control system stuff but temperature cycling is a for of oscillation. In general it means that there is a problem with the controls.



Cummins knew of the problem and they new the reason why. It was just going to take then a couple of months to go through all the "right" steps to get it fixed. That was just too long for me.



Here is the story that I was told: The cooling system for the RAM is the same as that of the V10. The V10 puts out >400Hp so the 6BT is over cooled. (This is really nice for the bombers!) The problem is the stock thermostat is too fast. It allows the system to heat up to 190+oF and then fully opens. The temperature drops quicky to 140oF where the thermostat completely closes. repeat...



This is what I have gathered from other posts:

The newer model is supposed to be a 2 stage and slower reacting. It may give some initial oscillation but should reduce to a steady state temperature around the thermostat's preset temperature.



I liked my 12V (6BT). I just did not like all the other problems that Dodge could not seem to fix. It was a Mexican truck and may have been a Moday/Friday car.



My 24V I really like. The extra 500RPM sweat range is really nice. It has had it share of issues. Same Dodge BS! They just can't seem to fix it the first time. My only big complaint is that my 12V got 22Mpg and the 24V get 16. 5-17. The 24V was supposed to get 5-10% better.

 

[Matt42]

Yikes! What an interesting array of, ahem, information. :-{} My experience here where it's almost always way over 100F obviously differs from the experience of others where it is a cool 90F. Then again, maybe my thermostat is comparatively laid-back.



I am still running the original t-stat. I also have read that Cummins has a newer version that reduces the open/close cycles. Does anyone have the Cummins part number for it?



Could the part number, from the Cummins box containing the new one in my hand, not yet installed, be 3928499?



The counterman at Cummins SW was amazed to have one in stock. They get five in, and all five go straight out the door, with orders for fifteen more.