As a cross check, you might try checking the sump oil temp immediately after
flying by dipping a long thermometer into the dipstick tube.
I have an O-360 A4A in my Archer with a very small oil cooler near the
bottom of the firewall. My problem until lately was too high an oil temp in
summer. At annual I asked my mechanic to check the vernatherm. He told me
it was OK. A bit later I pulled the vernatherm to look at it and saw the
seat on the plunger was not hitting the seat in the oil filter adapter
squarely. I had another mechanic install a new vernatherm and resurface the
filter adapter seat. The engine temperatures now look OK on summer
climb-outs.
I can't imagine my engine running too cold in the summer even with the
vernatherm stuck closed and routing all of the oil through the cooler. But
if it was stuck closed and the OAT was cool and I was running at 60% power,
it might happen.

Here is an interesting discussion of the factors affecting engine oil temp:

http://www.sacskyranch.com/eng18.htm
--
Regards,
Mike

http://mywebpage.netscape.com/amountainaero/fspic1.html
"Ross Richardson" wrote in message
...
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