Dan,

I never had the problem while living in SoCal, but had it in spades in
winter when I moved to Coeur d'Alene, Idaho.

My solution was a hinged aluminum plate on the outlet side of the oil cooler
activated with a Bowden cable to the cockpit. Simple and it works just fine.
Probably took all of two hours to rig it up. It allows quick adjustment of
the oil temp when the weather and/or flight regime changes.

Could it cause overheating in the summer if left closed? Sure, but like any
other aircraft system control, you gotta pay attention.

Dan Schaefer
Early 235, N235SP