I'm no thermos engineer and don't know a hell of lot about engine heat and dissipation, but I fell onto something that solved my overheating problem in a Gazelle and 550 Spyder I built. Both 1600cc engines were upgraded with bolt-on larger jugs and neither car had sealed engine compartments. Both engines had heat sensors and gauges and would overheat while standing still (South Florida). While picking up some oil at my local auto store I noticed a can advertising 100% synthetic and part of the specs on the side of the can mentioned better cooling than traditional oils. I gave it a try, whether it was my imagination or not but no more overheating problems. I've not seen the oil on the shelves lately but I think it was called Xonix or Zonix.