This is my first Cummins (had a CAT in previous coach). The pesky, expensive, prone-to-failure, Sauer-Danfoss hydraulic fan control gizmo on my rig is likely failed and my side radiator fan runs constantly at high speed. Some folks say fine since some ISL's tend to run hot due to variations in how some coach builders install cooling components, etc. The other school of thought is with fan running all the time, my engine may tend to run cooler than needed for optimum efficiency. I cannot find specs on what is optimal operating temp for the ISL 425 clean diesel engine. Today, pulling my CRV on a short, one hour trip in 70F ambient temps, my Silverleaf shows an average temp of 188 - 192 with a brief period of 195 when climbing a short grade.Is this generally too cool for the ISL or about right?

My ISL runs around the high 190s. Hotest it ever got was crossing the Rockies...207.

Fan on high will NOT cause the engine to run too cold. The thermostat determines how much coolant goes to the radiator. Very similar to operating in near-freezing temperatures-- the thermostat doesn't put as much coolant to the radiator.Yes, fan speed on high will lower temperature of coolant in the radiator AND take extra HP.

wolfe10 wrote:Fan on high will NOT cause the engine to run too cold. The thermostat determines how much coolant goes to the radiator. Very similar to operating in near-freezing temperatures-- the thermostat doesn't put as much coolant to the radiator.Yes, fan speed on high will lower temperature of coolant in the radiator AND take extra HP.Thanks for that clarification/reminder. I will not fret the failed fan controller. Can't find anyone who has one anyway and I am told the Sauer-Danfoss controllers many coach manufacturers use fail often.

Extra HP and better MPG and less fan noise are reasons that you may want to get your two speed/variable speed fan controller fixed.

Check the 12v fuse going to the controller -- If it`s blown, the fan will run on high speed -- You will probably have a hard time finding the fuse -- The best way to check, is disconnect the connector at the controller, & check for 12v power there -- Bill Willard

ISL 'normal' operating temp | Good Sam Community

15 Replies

mmccwill
Explorer
Aug 20, 2013
Check the 12v fuse going to the controller -- If it`s blown, the fan will run on high speed -- You will probably have a hard time finding the fuse -- The best way to check, is disconnect the connector at the controller, & check for 12v power there -- Bill Willard
wolfe10
Explorer
Aug 20, 2013
Extra HP and better MPG and less fan noise are reasons that you may want to get your two speed/variable speed fan controller fixed.
smlranger
Explorer
Aug 20, 2013
wolfe10 wrote:
Fan on high will NOT cause the engine to run too cold. The thermostat determines how much coolant goes to the radiator. Very similar to operating in near-freezing temperatures-- the thermostat doesn't put as much coolant to the radiator.

Yes, fan speed on high will lower temperature of coolant in the radiator AND take extra HP.

Thanks for that clarification/reminder. I will not fret the failed fan controller. Can't find anyone who has one anyway and I am told the Sauer-Danfoss controllers many coach manufacturers use fail often.
wolfe10
Explorer
Aug 20, 2013
Fan on high will NOT cause the engine to run too cold. The thermostat determines how much coolant goes to the radiator. Very similar to operating in near-freezing temperatures-- the thermostat doesn't put as much coolant to the radiator.

Yes, fan speed on high will lower temperature of coolant in the radiator AND take extra HP.
Blaster_Man
Explorer
Aug 20, 2013
My ISL runs around the high 190s. Hotest it ever got was crossing the Rockies...207.

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ISL 'normal' operating temp

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