Well, you wouldn't have the fan running that much if you're just at idle. I have had to problems with just putting the temp. guage right up to the head and I get a great reading. My temp. gun can read up to 20ft. but I just get close to where I know it's accurate. Now, if you were checking the head temp on a plane with the engine running, then the prop could have signifigane impact on what reading you will get. But, if you get close enought to the head, then you should have not problem. There is usually some part of the head you can measue the temp. Sometimes I'll just take off the canopy, and check right beside the glow plug.

To me, there is not need to take the engine temp reading on the backplate. You really need to check the head, and side case temps. The backplate will not be the hottest part of the engine for obvious reasons, but the head will, since that is where all the action is taking place (explosion, movement of cylinder, etc.). Like I said, I was talking about a "running temperature" of around 210-215° you should have the head be running. If not at this temp. proper expansion will not take place.

How that helps

~Michael~