where to point the ir thermometer
 

one of my 4 diesel buggers is running a little hot. and it is the one with an aluminum head. naturally. 86 300sdl to be exact. have changed thermostats and the fan clutch. before i remove/replace radiator i decided to buy an ir point and read thermometer. a radio shack schmengie unit for $50 and change. question. in order to determine that my temp guage is correct and indeed i am running a little hotter in the 86 than the two 83s and the 84, where do i 'point' the thermometer? water pump assembly? top hose? bottom? thank you in advance. oh on the 'little' hot. seem to see 100 celcius on the highway. sometimes 100 + a little bit. the others do not approach this point. one clue to temperature sending unit problem is the the item in question comes up to temperature much more quickly than the other three. but then i be not sure of anything at this point. lastly, the 86 has 185k miles and by the looks of things the radiator seems not to be original.

I would suggest that you 'map' the radiator. Take readings vertically every 4" in 4" 'strips.' Then, look at the readings for uniformity.

I would expect higher readings on the upper rows, and lower readings on the lower rows. You might also get readings a bit cooler in the center, where the fan pulls air over the radiator.

Also, you can try this as it first warms up, looking for where the radiator first begins to warm up. If a vertical coil is plugged, it will warm up slower.

Best Regards,
Jim

Did you adequetly purge the air out of your block after you put the new thermostats in?

Those Infrared thermometers are neato :)

gentlemen, thank you. and yes i believe i purged the cooling system. had the front end up on ramps. and my drive way has a slope so the front of the car was much higher than the rear. at operating temperature the thing idled with the radiator cap off the resevour. for maybe ten minutes or so. this sound about right?