I posted about how I put a shutter in front of the oil cooler on my 6. I was still getting low oil tempertures in the cold, even with the shutter completely closed. What I did was to insulate the oil cooler all around the outside of the unit, as some suggested. I used thin closed cell foam used as packing material. It's maybe 1/8" thick. I put on a few layers and went around the entire thing with duct tape. On the back where the air comes out if the shutter is open I put one thin layer with a seam down the middle. This way if I open the shutter it will blow through. It is not pretty but it raised my temps for sure. Today was not as cold as it has been so I flew up to 8500' and throttled back and cruised. I was up to 200 degrees after the climb then it fell to about 190. I've never seen temps that high, especially in the cold weather. At 8500' it was 35 degrees outside. I'm doing better for sure. On the next real cold day I'll try it again.
