Engine/Transmission (1994 - 1998) Temperature cycling

[RJ2]

Towing a trailer on the interstate the temp guage would cycle 190 to 150 ,constant. Read a post on this subject from july 2001, mainly the jest was either normal or hard on the engine because of drastic temp drops .

Is there any new perspectives on whether there is really

an issue of the engine getting a blast of cooler water constantly. Or is the temperature guage in need of replacement? Thanks RJ

 

[SlyBones]

I believe that temp cycling is normal for a 97. Mine did it even empty when I first got it. Read lots of post about the thermostat that is supposed to fix this. Saw lots of debate over which was the correct part number. So I got both. Pulled the old and checked the PN. Used the other one. For get the number would have to go and look it up.



I find that this one is just slower. Maybe that not the right word, but now the truck warms up slower than before, however does not cycle while empty.



Towing on a hot day and the temps still cycle, just not as fast a cycle as before.

 

[illflem]

It's just that the Cummins cooling system is overbuilt unless you're towing 20k in 110° temps. You're seeing the tsat opening and closing. When I tried the "new improved" tsat my rig quit cycling but ran too cold. Went back to a 190° and don't let the ups and downs bother me.

 

[drees1]

Does the new t'stat offered solve this problem?? I would like to know. I don't care what Cummins or Dodge says about this cycling being ok. It's not. Low cycle thermal fatigue will aggrevate head cracking and head gasket problems. Why should I change a leaky head gasket at 250,000 miles when it could have gone 400?? Mine is a '96 and they are prone to leaking at the head gasket externally near the thermostat housing. Is that a coincidence??



The problem is related to the thermostat design, mainly. A large thermostat with high pump pressure does not have to open much to cool a lightly loaded engine. The response time of the T'stat or sticking are the source of the problem. It is not good engine design in my opinion. At CAT and Cummins, we had specific tests that cycled hot and cold water through a running engine to prove out durability in head gasket and head casting design. Every time the engine's temp changes the head gasket must cope with creep between a head and block that may move at different rates as hot and cold water is cycled through the engine. WHY PUSH IT?



P. S. What is the P/N of the new T'stat??



Doug Rees

 

[Matt42]

Originally posted by RJ2

Towing a trailer on the interstate the temp guage would cycle 190 to 150 ,constant. Read a post on this subject from july 2001, mainly the jest was either normal or hard on the engine because of drastic temp drops .

Is there any new perspectives on whether there is really

an issue of the engine getting a blast of cooler water constantly. Or is the temperature guage in need of replacement? Thanks RJ

The temperature cycling is pretty much normal on the 94s thru the 97s, and maybe the 98s as well. The owners manual that came with my 96 warned me that would happen. Watching the guage cycle gives me something to do when pulling up hills, and I don't worry about it. I also have also heard that an updated thermostat is available. I may install one some day.



I don't think that there is an issue about problems due to coolant temperature fluctuation. If there was, we would hear about a lot of cracked heads and blocks, even without any help from propane injection and other BOMBs.



By the way, the temperature guage cycle and the fan clutch engaging and disengaging are not directly related, so don't expect much correlation between them. The highest temperature I ever had on mine was about 210. That was pulling up the grade from Sacred Mountain into Flagstaff in June, towing, at the legal speed limit.

 

[Missouri Mule]

Mine temp changed a lot when newer but now it has settled down and does only occasionaly.

Never been over 190.

Cummins/Dodge states normal condition.

I will have to agree the temp fluctuation is so quick I wouldn't think any part of the engine except coolant/t-stat/temp gauge knows it.

The gauge usually cycles from 140 to 180 (180 to 140) every 10 seconds and then finally settle down at 180.

 

[Joe G.]

My 'stat is the original. 191K miles so far. It has always cycled. I have a hard time thinking that a change in coolant temp from about 150 to a little less than 180 could possibly be a problem. That's a coolant temp change of 30 degrees or less. I doubt the iron is changing that much. Other parts of the engine have to have a normal temp change of a lot more than that. For example, pulling a grade and then going down the other side should cause a pretty big temp change in the iron near the combustion chambers. A lot more than 30 degrees.