I have an
oil cooler with a 180 degree thermostat. The engine builder recommended 20/50 viscosity
oil. The A/F ratio at 7300 RPM on one pull was 12.6 and on the second pull at 7500 RPM was 13.0, lean! The A/F at 6500 RPM was 13.2 and 13.2 during both pulls, so the engine was running lean during both full pulls with a max A/F of 13.9 at 5100 RPM during both pulls.