[Pillow]

>the cooler fan switch should go at the cooler outlet so if the cooler cannot keep the desired 180deg oil it will cycle on and cool the oil without overcooling if the cooler does not need the fan to keep up. <

100% correct Kdanie. The absolute best place to check oil temperature is AFTER the oil cooler.

This can really only be done on an external cooler setup as the stock T1 and T4 have no place to monitor oil temps except from the sump plates, which is a compromise.

The real concern is what temperature the oil is when it hits the bearings and so forth. So on a full flow system this is the oil flow returning from the oil cooler. Once the oil has settled into the sump it is hot from being "used" to cool the heads or through the bearings.

The only reason the sump plate temp sensor locations work is that the oil flows quickly enough that the readings give a ball park estimate of how the engine is doing at cooling the oil.

On a well engineered oil system the oil will quickly warm up to 180-190 and stay there.