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Towing with our 2018 Cayenne. Was running with the A/C off thinking I was easing the load on the engine. The oil temp modulated a few degrees around 230F. Started to get hot in the cabin so I switched on the A/C and within a few minutes the oil temp decreased to 210F and stayed there. Was a bit surprised so I turned the A/C back off and within about 3 minutes the oil temp started rising again so back on with the A/C and lower oil temps. Can anyone explain why this happens. Seems a bit counter intuitive to me.
 

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When you turn the AC on you also turn the fans on the radiator to max speed. Since there is an oil cooler on the engine chances are the increased airflow over the cooler will result in decreased oil temperature. Is there a reason you're turning the AC off? It's most efficient when run in full "Auto" mode. The compressor is a variable displacement compressor so when it's not needed it basically goes into an idle mode and doesn't compress any of the refigerant.
 

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Thanks for your reply and explanation. I guess running with the A/C off to ease the engine load (and hence keep the engine running cooler) is old school thinking.
Pretty much. The thinking now is AC is a fuel saving device, since the vehicle has more resistance pushing the air aside if the windows are open. Closed windows and AC running it the most efficient way to drive the car.
 
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