Coolant guage goes back to cold after being shutdown for 20 minutes

[The motor guy]

I have two dodge cummins trucks. One will pretty much stay up to temp most of the day when making frequent drives around town, my other truck, you can stop at dairy queen for lunch and it will be back all the way down at the minimum 140 mark. Of course it goes back up to temp once faster once you start driving though in a short bit. Opinions?

 

[edyvw]

I have two dodge cummins trucks. One will pretty much stay up to temp most of the day when making frequent drives around town, my other truck, you can stop at dairy queen for lunch and it will be back all the way down at the minimum 140 mark. Of course it goes back up to temp once faster once you start driving though in a short bit. Opinions?

Same engines etc?

 

[zrxkawboy]

Are they the same year? Maybe the way the computer controls the temp gauge varies between model years.

 

[dumkid]

Different radiator design? One engine thermo-siphons?

 

[Dave9]

Research it in a Dodge/owners' forum. Possibly it is a *dumb* gauge that doesn't actually show accurate temp, just moves the needle to indicate hot/cold? Are you the original owner and/or certain that it didn't have the temp sensor replaced with the wrong one? Does the gauge appear to move linearly as it warms up? Well I mean with the obvious deviation that happens when the thermostat opens.

 

[The motor guy]

Same engines etc?

Same engine block, but one is 5.9 liters and the other is 6.7

 

[edyvw]

Same engine block, but one is 5.9 liters and the other is 6.7

Do they use same materials in block and head? Under engine protection? Engine covers? Cowlings?

 

[The motor guy]

Do they use same materials in block and head? Under engine protection? Engine covers? Cowlings?

Yes both are big hunks of iron. Probably a computer thing

 

[edyvw]

Yes both are big hunks of iron. Probably a computer thing

Something is dissipating heat, maybe an auxiliary water pump. Is heating the same in both vehicles after parking, or does one where the temperature falls faster has weaker heating?

 

[The motor guy]

Research it in a Dodge/owners' forum. Possibly it is a *dumb* gauge that doesn't actually show accurate temp, just moves the needle to indicate hot/cold? Are you the original owner and/or certain that it didn't have the temp sensor replaced with the wrong one? Does the gauge appear to move linearly as it warms up? Well I mean with the obvious deviation that happens when the thermostat opens.

It acts just like the newer 07 truck. Just cools off quicker. They didn't maintain the coolant in this truck though. Possibly the probe is gummed up?

 

[Dave9]

If there is goop buildup on the business end of the sensor, it should just lag slightly in response to temp change. Any chance there is air in the system and the sensor is not in contact with coolant?

 

[The motor guy]

If there is goop buildup on the business end of the sensor, it should just lag slightly in response to temp change. Any chance there is air in the system and the sensor is not in contact with coolant?

There shouldn't be. It's done this for a while now. The engine stays good and hot for even a couple hours after shutdown using the hand test.

 

[Gasbuggy]

That's interesting. My CTS-V will hold heat for hours.

 

[eljefino]

Get an infrared thermometer and gather data off the thermostat housings and other spots in common.

 

[ElectroMechanoMan]

I had 2 5.9L Cummins , 160hp& 180hp. 1992 and 1994. They wouldn’t warm up unless they were moving. They would idle and never come off of cold. Drive a couple miles and they would warm up, but the temperature gage would cycle from center of scale to roughly 1/4 scale. Cummins N Power mechanics said it was do to a very oversized radiator. I don’t recall how fast they cooled off, but if I ran them hard, I’d idle them a few minutes before I shut them down.

 

[kschachn]

I had 2 5.9L Cummins , 160hp& 180hp. 1992 and 1994. They wouldn’t warm up unless they were moving. They would idle and never come off of cold. Drive a couple miles and they would warm up, but the temperature gage would cycle from center of scale to roughly 1/4 scale. Cummins N Power mechanics said it was do to a very oversized radiator. I don’t recall how fast they cooled off, but if I ran them hard, I’d idle them a few minutes before I shut them down.

That sounds more like a thermostat problem to me. The coolant isn't really getting to the oversized radiator unless the thermostat is allowing it to do so.

 

[The motor guy]

I had 2 5.9L Cummins , 160hp& 180hp. 1992 and 1994. They wouldn’t warm up unless they were moving. They would idle and never come off of cold. Drive a couple miles and they would warm up, but the temperature gage would cycle from center of scale to roughly 1/4 scale. Cummins N Power mechanics said it was do to a very oversized radiator. I don’t recall how fast they cooled off, but if I ran them hard, I’d idle them a few minutes before I shut them down.

All diesels are like that. My questiom is how come I can drive 20 miles, eat lunch for an hour and come back out and have the temp guage back at zero. My 6.7 won't do that. It maybe like halfway after an hour or so..

 

[dumkid]

All diesels are like that. My questiom is how come I can drive 20 miles, eat lunch for an hour and come back out and have the temp guage back at zero. My 6.7 won't do that. It maybe like halfway after an hour or so..

Has it always done this? If it's always cooled down quicker than I wouldn't worry.

 

[The motor guy]

Has it always done this? If it's always cooled down quicker than I wouldn't worry.

I haven't owned long enough to know. I did throw a new thermostat and change the coolant when I got it. I would think a big cast iron block like that would hold heat for quite a while. I can barely touch the valve cover like 3hrs after driving, so no way that temp guage is accurate

 

[dumkid]

I haven't owned long enough to know. I did throw a new thermostat and change the coolant when I got it. I would think a big cast iron block like that would hold heat for quite a while. I can barely touch the valve cover like 3hrs after driving, so no way that temp guage is accurate

If the engine stays between 180 and 200 and the temp gauge moves with the engine temp then it's fine