Oil Temperatures

I have a Cessna 172F with the Lycoming O-360 conversion and a C/S speed
prop.

My oil temperatures are always low. I pulled the probe and place in in a
can of oil heated to 180 degrees and had a calibrated thermometer beside
it. I marked the meter in the plane so I know where this temperature is.
Even in the summer I cannot reach that temperature. I have the oil
cooler mounted on the back of the rear baffle on the port side of the
aircraft. It has run cool with the old engine and two years ago I
installed a factory overhauled engine. Any ideas why it stays so low.

Ross