If you use a temps gun like grubster1 (and myself) use, you must point the laser light on the cooling head, and not on the glow plug, because the laser light is about 1/2" distant from the sensing element. So if you point it at the glowplug, you will have a temp of "XXX" and when you move it to the cooling head, the temps will rise from a good 50 to 60 degre