BillJ, sometimes I think that people put too much emphasis on how fast an engine can turn a prop. You can lightly load an engine enough and get extraordinarily high rpm figures but this does not necessarily equate to performance. I used to fly a Byron Pitts with a Tartan twin on glow with no nitro turning a 20x10 Zinger. I don't remember what the max RPM was but it was a terrific performer. I never had any over heating with this combo because it was running on glow fuel, which runs cooler than gasoline, and I had very good air flow through the cowl. Most of my running was in the air and not on the ground. Of course the engine picked up quiet a bit of RPM while flying. What is your cooling air flow situation when you are experiencing the over heating problem?

Actually adding more oil to the fuel probably adds to the problem by creating more friction thus more heat. The vaporization of the alcohol does most of the cooling. As I recall back in the days (1985-87) when I was running the Tartan, I would buy a gallon of FAI fuel containing 21% oil and cut it with 2 gallons of methanol making 3 gallons of 7% oil mixture. How much oil are you using? Before you go try 7% oil lets here from some other Tartan twin users to verify or correct that figure.

Ken