I've never checked any of my engines, but it seems like around 200 F is about right. MIP (I think) makes a real nice "on board" thermometer. I think it loops around the cylinder or head with a noose type thermocoupler. It seems R/C car guys tend to pay more attention to engine temp. I read that temp varies greatly depending on where you take the reading from, and it can be difficult to compare different engines due to head and cylinder fin designs. Some rely on the "touch" test or the "spit & sizzle test", but as long as an engine runs strong and does not show high temp discoloration of piston or burn up plugs, it's ok.