Just took my 97 out for a shakedown run. Didn't pan out perfectly. I don't care too much for the transmission when it locks up. It seems to put an awful lot of torque and weight on the lock up clutch all at once. The truck is running at about 2 K RPM and when it hits 50, it locks up and drops the RPM to about 15-1600. Is this normal? Also, the truck was running on the 1 of 190 on the temp gauge, and then it dropped to 140 and didn't come back up the rest of the trip. I thought it might be a problem with the coolant but I checked the temp with my finger in the radiator and it was not even luke warm. Also, the block was just barely warm to the touch. What would cause this? I know running hot is a common and bad problem, but how many people complain about running to cool? It was about 38-40 degrees outside.
Thanks
Chris

 

Sounds like the thermostat is stuck open, I would suggest replacing it. The trans sounds in line I think 3-400 for lock-up is par.

 

The rpm drop for the lock up sounds pretty much normal. The eng temp sounds a little low. You should replace the T stat. The finger in the radiator trick doesn't really mean much other than the coolant in the rad is cool. When the t stat cycles and closes the rad cools down.

 

I bet your heater don't get very warm either! Thermostat would be my guess.

 

If it went up to 190 then dropped to 140 the thermostat might be working OK.

Do you use winter fronts or a cardboard radiator blocker?

I have to, or I never get warm.

 

I vote for a stuck T-stat on the temp drop. Even on my truck it will drop 50 degrees but it always comes back up to 190*F mark.

140 and lower is hard on the engine...

 

If the T-stat was stuck open it would most likely never hit 190 then come down.
What Chris decribes sounds perfectly cold weather normal for a 12 valve.

 

Yep. Sounds about right for me too...both on the T'stat and the lock up. However, my truck does give lots of heater heat. Put the truck to work and find out what the temps are like.

 

I am going with the stuck open thermostat. I had just drained the radiator a few days prior and put new coolant in. Probably dislodged some stuff. I had wanted to do the thermostat then but the Cummins dealership didn't have one available. It just was a brain fart. I should have known that needed to be done but didn't do it and had to pay the price of doing a job twice. That antifreeze sure is expensive now.
Just for clarification, the temp did go up to 190 for a while, but for the rest of the day, it would not go above about 145-150 area. I figure, when it opened, it stayed open and the coolant just wouldn't heat up. I had to run it about 300 miles like that, the heater did work, so I know it was at least a little warm. Do you all think I might have damaged anything? I sure hope not.
Chris

 

I wouldnt think it would have hurt anything, since 160 really isnt cold.

 

Long term you might have but a day or two cool like that... no I don't think you hurt it a bit...

 

Nothing wrong with your thermostat, that is normal behavior for that engine in winter. The cooling system in your truck is much more efficient than it needs to be and unless you put a load on it, you won't see anything higher in the winter if the outside temps are low.

Mine will climb to 190, and then drop to about the same level and stay there unless I put my winter cover on.

 

eng208
If you change the Tstat can you report back the results?
I always thought a Tstat would close to maintain opperating temp if the rad cooling was to much?

 

It does but the large built for a load radiator is sitting there with nothing flowing though it, the coolant in it is about the same temp as the outside air. The coolant in the radiator never really warms up. The stat only needs to open for a second to lower the temp enough to close the stat again, that's why you see the temp needle going up and down and never getting real hot. Totally normal price you pay for being able to tow 20k pounds up a pass in the Arizona summer without overheating.

What 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

GAUGE FLUCTUATION WILL BE NOTICED MOST OFTEN UNDER STEADY STATE (HIGHWAY) DRIVING. PLEASE ENSURE THAT YOUR CUSTOMER IS AWARE OF THIS NOTE PRIOR TO RELEASING THE VEHICLE.

 

I replaced it. Now it is going to 190 and then dropping, then warming to 190 and dropping again. This I believe is normal. It would not warm up before. Thank you all for the help.
Chris