I posted this on the Gen. perf. forum but didn't get any replies so I'd like to try it here:
<TABLE width="100%" border=0 itxtvisited="1"><TBODY itxtvisited="1"><TR itxtvisited="1"><TD vAlign=top itxtvisited="1">I recently bought a non-contact digital thermometer. I needed it to check cooling systems and trans cooler lines. As I was reading the instructions, I noticed it shows the tool being used to check difference in temp at the exhaust manifolds. The instructions are very vague and don't explain what your suppose to check. I'm guessing an inefficient cylinder will exhale a different temp than one that's burning clean, but will it be higher or lower? How much difference should I be concerned with? I'm sure a completely dead cylinder will be cold, right? But what about an injector that's spraying to little or to much? What other engine test can I use it for?

Thanks
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We use these extensively at work and I am sorry to tell you, that despite what the marketing literature says, these devices are not suited for engine temperature diagnosis. These use IR light reflection to infer the surface temperature of the target, not the temperature of the fluid inside.

For a non-contact thermometer to actually tell you the temperature of the fluid in question would require changes in the thermometer's calculation based on the emissivity of the surface in question, and then extensive thermal conductivity calculations based on the materials between the surface, and the fluid in the block\transmission\etc. And even then, the data still would not be conclusive because the fluid circulates rapidly and the temperature is different in various spots.

I have a lot of experience with thermal imaging and I myself would not be using one of these for temperature measurement of internal fluids in an engine. The temperature the device tells you is not the temperature of the fluid inside the block because of the reasons I described. It is useful for showing trends of the temperatures across the engine (which parts are warmer than others) but the numbers you see aren't going to be very reliable. If you want close numbers of your coolant's temperature, a mechanical guage with a sending unit bulb that threads into the block's water jacket is the way to go. Because of the thermal conductivity of the engine block and the junction between the block and ambient air, the coolant circulating through the engine will be warmer than the surface temperature of the block in most cases. The IR thermometer may get lucky and get close, but because of pure thermodynamics, this is not guaranteed.

If you're trying to use the thermometer to find a dead cylinder, I don't think it will help you much since the entire block gets hot assuming most of the cylinders are firing. A much more reliable and trusted method of finding a dead cylinder is to pull plug wires one-at-a-time while the motor is running and see if anything changes. If you pull a plug wire and the motor runs the same way, that cylinder was most likely not firing. A routine check of the ignition system and a compression test are also ways to find a dead cylinder.

That's my 2 cents...