Cummins 6.7 temp goes up when I stop while towing, anyone know why?

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Hey all, not really a concern just curiosity, when I tow my travel trailer and stop at a gas station or something then put it in park and leave it idle (I always leave it idling on short stops) the oil And coolant temperatures shoot up about 10 degrees and eventually go back down, or go down right away when I start driving, I assume this is just residual heat from the engine block and the fluids aren’t flowing as much due to lower rpms but am curious if there are other things possibly emission related or who knows what going on.
 
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The reason is the coolant is flowing a lot slower at an idle and the heat in the engine has more time so soak into the coolant and oil inside the block. Since the engine is not working hard, the cooling system catches up after a brief while.
 
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The reason is the coolant is flowing a lot slower at an idle and the heat in the engine has more time so soak into the coolant and oil inside the block. Since the engine is not working hard, the cooling system catches up after a brief while.
plus less airflow through the rad with the vehicle stationary. the fan can only do so much.
 
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I had much the same thing happen to my Volvo 740 Turbo while driving fast on a very hot day. It must have been about 100 F. It was fine while I was moving but the temperature rose alarmingly when I stopped for gas.

I assume it was residual heat in the turbo and the block combined with lack of sufficient radiator cooling due to less airflow and the high ambient temperature.

The radiator was also semi plugged (inside and out) and when that was cleaned it never happened again.
 
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what type of cooling fan on that? what temps are we talking about?
Some variation is normal.. but also why ford went to dummy gauges on many vehicles.. to stop complaints about normal operation.
 
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what type of cooling fan on that?
It's an electronically controlled mechanical fan clutch. They fail in 2 ways. Usually about 80k the clutch is just plain wore out.

The second common failure is the wires that run to the clutch get wrapped around the fan which pulls them out on both ends.

Both ends being the actual clutch and the vehicles wiring harness.
 

Big E

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The oil temperature reading is fake. There is no oil temperature sender unit on the Cummins Rams.

Just FYI.
 

Jaymie

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Interesting that the oil temp reading is fake, so there’s actual rtd temp sensor, it’s just calculated by the computer?
 

Big E

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Oil pressure and temperature reading are calculated by computer algorithm.

The pressure sending unit is a 6psi on/off switch. There is no oil temp sending unit. Only coolant.
 

JHZR2

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Those trucks were known for fan clutch failure. I have literally replaced hundreds. Gotta get one from the dealer. Aftermarket ones are junk.

Also check for dirt,bugs,leaves etc between the coolers.
Fan clutch was the first thing that came to my mind too. Can hear it engage and disengage on the 5.9 engines at least.
 

Jaymie

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Update, I used the high idle with the ac on (fan came on) and the temps didn’t climb at all, not sure if I’m actually helping anything but I’ll continue to do this.
 
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You can also turn the air control knob to defrost (windshield) with the cabin fan on and that also starts the radiator fan and the ac compressor without the need to turn the ac on. At least in 2 of my cars with electric fan it does that. My other 2 cars the fan is mechanical and running all the time. Also give it some gas (e.g. 1500 rpm instead of 700) while in idle to get the water pump running faster and you see the temperatures drop quicker. But all these are putting more load on the engine ...

Eventually best is to get some air flow and start moving without any ac. Overall, cars are designed to handle this and I wouldn't worry too much.
 
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Interesting that the oil temp reading is fake, so there’s actual rtd temp sensor, it’s just calculated by the computer?
correct the computer calculates the oil temp and the oil pressure...

FWIW my 2012 does the same thing as yours and my tranny temp climbs more than the coolant usually. After 6 years of ownership, I don't worry about it. I've been using it for towing since I got it. I have learned that as soon as I start moving again both coolant and trans fluid temps drop back down. I keep my trans below 200F and the radiator fan doesn't come on until 217F unless you force it like others stated above. I let my truck idle when towing as well, but don't use the auto idle unless I need it warmed up, the temps you are seeing won't hurt the truck.

just my $0.02
 
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What year truck? Old trucks often have a belt driven fan. If so, replace it with an electric thermostatic fan
 

Jaymie

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correct the computer calculates the oil temp and the oil pressure...

FWIW my 2012 does the same thing as yours and my tranny temp climbs more than the coolant usually. After 6 years of ownership, I don't worry about it. I've been using it for towing since I got it. I have learned that as soon as I start moving again both coolant and trans fluid temps drop back down. I keep my trans below 200F and the radiator fan doesn't come on until 217F unless you force it like others stated above. I let my truck idle when towing as well, but don't use the auto idle unless I need it warmed up, the temps you are seeing won't hurt the truck.

just my $0.02
Thanks for the input, its good to know that it’s a common theme among these trucks. I wonder if they went with a calculation so that a failed temp sensor doesn’t result in a truck on the side of the road.
 

Jaymie

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What year truck? Old trucks often have a belt driven fan. If so, replace it with an electric thermostatic fan
It’s a 2018, I got a great deal on it when the new style started hitting lots, thankfully I got it before they started jacking up the prices, my buddy bought a new Chevy diesel and he paid like 6k over the sticker price.
 
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