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Old 05-22-2016, 02:57 PM   #1
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Engine/Allison Trans Temperature differential ?

For the Technical cummins engine guys out there? I have a Silver leaf engine/Trans monitor running. Cummins 350 ISC, Allision 300 tranny. My engine temp stays at 180-181 consistently (even up hills is Co.). My transmission temp varies a lot. And has been as high as 208F. All within normal operating temps, from what I have read. But, I'm puzzled that the temp difference between engine and tranny could be as much as 25-28 degrees? Any evidence of a lingering issue?? Thanks
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Old 05-22-2016, 04:45 PM   #2
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Mine does about the same thing on small hills but on flat ground the transmission runs about 10F cooler then the engine. On hard pulls the transmission will get hotter then engine, I have to down shift to keep RPM's up to keep tranny cooler.

I have a 350 ISC with side radiator, which I think has better cooling capacity then rear radiator.
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Old 05-22-2016, 04:50 PM   #3
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Ok. Thanks. No big deal then! Mine has side radiator also.
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Old 05-22-2016, 05:19 PM   #4
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Allison has been quoted stating there is no problem with the transmission temperature even as high as 240.
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Old 05-22-2016, 05:51 PM   #5
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Quote:
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For the Technical cummins engine guys out there? I have a Silver leaf engine/Trans monitor running. Cummins 350 ISC, Allision 300 tranny. My engine temp stays at 180-181 consistently (even up hills is Co.). My transmission temp varies a lot. And has been as high as 208F. All within normal operating temps, from what I have read. But, I'm puzzled that the temp difference between engine and tranny could be as much as 25-28 degrees? Any evidence of a lingering issue?? Thanks

Congrats on running the Silverleaf. "Knowledge is power". I'm not sure how CC cools the transmission fluid. If your fluid cooler is internal to the engine radiator, then the tranny temp will slowly rise to a few degrees above the engine temp. Long hard up grades will cause the engine temp to rise above the transmission. The place that will push the transmission temp up is stop and go city driving or extensive idling while in gear. The torque converter is a big producer of heat. If you get caught in a traffic back up, set your brake & sift to neutral. Temp will go back down.

Watch that Silverleaf. It will make you a better driver.
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Old 05-23-2016, 09:08 AM   #6
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Interesting... Mine will cool down in the city. Warms up when I'm pushing it at around 68 MPH...Hills etc... But has never topped 208 F... sometimes there is too much information to watch on the Silver Leaf..
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Old 05-23-2016, 10:49 AM   #7
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Your coolant temp of 180 is to cold. The ISC should run at 195. I think you might have a problem with your fan controller or one of the sensors. Running to cold will have an effect on your fuel mileage.
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Old 05-23-2016, 12:17 PM   #8
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Your coolant temp of 180 is to cold. The ISC should run at 195. I think you might have a problem with your fan controller or one of the sensors. Running to cold will have an effect on your fuel mileage.

Not necessarily too cold. The Cummins engines back in that era, before EGR was added to the fuel system, had thermostats designed to open around 180. When on level ground, with boost pressure low, my 2002 built ISM runs plus or minus 180. The thermostats were changed as emission controls were added. This started for Cummins with engines designed to meet '04 and later EPA requirements.
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Old 05-23-2016, 12:38 PM   #9
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My 2002 Windsor with 350 ISC runs at 180F, that's when the thermostat opens. It will get hotter climbing hills etc but will settle back down to 180F
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Old 05-23-2016, 01:45 PM   #10
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Yes I thought so too in the beginning. But Cummins Southwest confirmed its running at design temp... I would prefer that it run hotter to ensure complete fuel combustion. but cummins says it's fine!
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Old 05-23-2016, 06:52 PM   #11
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My engine temps are virtually the same, regardless of outside air temp. The Allison is much more outside temp sensitive. If hot it runs warmer than if cold.
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Old 05-23-2016, 07:04 PM   #12
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All comes down to trans cooler type and location , my trans cooler is a heat exchanger in the lower rad hose, on a side rad chassis.
So the coolant from the rad cools the trans before it gets back into the engine.
Trans temp always a few degrees lower than engine , and when coasting or using the exhaust brake , drops considerably lower.
Trans temp will start to get above engine , if stuck in traffic , then I know it's time to shift to neutral and let the trans cool off.
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Old 05-23-2016, 11:15 PM   #13
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Sorry guys but what I have been told by Cummins is that the ISC should run at 195. Mine has run at 195 ever since new until the fan controller went south and then it ran at 180.Changing the controller brought it back up to 195.

It looks like there is some confusion with Cummins as to what the correct temp should be
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Old 05-24-2016, 07:02 AM   #14
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Sorry guys but what I have been told by Cummins is that the ISC should run at 195. Mine has run at 195 ever since new until the fan controller went south and then it ran at 180.Changing the controller brought it back up to 195.

It looks like there is some confusion with Cummins as to what the correct temp should be

If you plug your engine serial number into the Cummins Quickserve app, you can see the operation temp range of the design thermostat. The opening temp is the bottom of the normal operating range and the wide open temp is the top. Mine is 180-201.
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