Of course, that's if I can see past the A/C to the plugs...exhaust manifold temps work too if you check when engine is still almost cold and you can tell which are heating up fastest.

My IR sensor was designed to check fuser roller temperatures on a laser printer. Big investment, used it only twice for that, but I use it for just about everything else! Drafty windows, locating missing caulk around doors and windows, check my 70 year old oven's temperature, etc.