Not an RV12, but the same situation no matter what airplane you are flying. I have an RV6 with my oil cooler mounted on the firewall, fed through a 3” scat tube from the #4 baffle. I have a butterfly valve in the scat tube feed controlled from the cockpit. This time of year in southern Ohio, it’s closed all the way 100% of the time, and I never see above 160* OT. The last week or so with ice cold OAT’s, I don’t get above about 145. The butterfly shuts off all of the air, so the only other thing I could try is to cut off oil supply to the cooler. Not willing to do that - too many failure points. An experienced aircraft engine guru from here told me that if I’m seeing 160*, I have nothing to worry about. Internal crankcase pressure is slightly lower, so is the boiling point of moisture. But mostly there are hot surfaces inside the engine that will flash off moisture in an instant. Like piston skirts that get splash oil every revolution. They can be as high as 500-600*. Lycoming agrees, because their recommendation for long term engine health is to maintain oil temps above 160. I’m planning on flying tomorrow during our “heat wave” - temps may hit 35* and it’s supposed to be sunny. Even though temps around here have been sub-zero lately, my hangar temp doesn’t dip below 40* usually. I still preheat, so my goal is to see how hot I can get my oil - 160 or above - and hold it there for 20-30 minutes. All engines, including Rotaxes, should behave similarly relative to operating oil temperature vs moisture.