"Engine" Temperature Measurement.

[RPOL88]

I have a 66 Chevelle 138 car with a 71 402 in it. Under "normal" driving conditions the aftermarket heat gauge would read 215 t0 225 and go up from there. This was really bothering me. New 4 core radiator and shroud. New high volume water pump, stat, hoses, and whatever else. NO CHANGE. (over $600.00)A friend noticed that the heat gauge was hooked up to the head instead of the intake manifold and told me the gauge that reads head temperature is calibrated differently. Advised me to take my wife's thermometer used for cooking and stick it in the radiator. It does not waver above 182 degrees. Wish I talked to him $600.00 ago.

[mockingbird812]

Tom,

Glad you figured it out. But, that is a very good reason for having a procedure to know what your coolant temp is (and WHERE to measure it). Gauges can be way off. Thanks for your story. You may have spent $600, but you are "bullet proof" now and have one less thing to worry about.

[Dusk Blue Z]

Sam,

Spot radiometers are like digital cameras, the more they cost the higher the resolution and the narrower the field. I think you’re about right with the 4” target size estimate. The reason the instructions state that it is "Not recommended for measuring on shiny surfaces” is because heat is reflective. Try and measure the temperature of the chrome on your bumpers on a sunny day…

As a coincidence guess what the emissivity of black electrical tape is, yup 0.95. That’s the reason Thermographer’s use it as a constant.

On a practical note I don’t think you are trying to hold a set temperatures like some manufacturing process need to do, just trying to make sure the gauge is reading close. Based on your thermometers accuracy I would just cover the top of the thermostat housing with electrical tape to get an even surface coverage. Start the engine and watch the temperature rise. You should be able to see when the thermostat opens and closes. Just compare these readings to what is being seen on the gauge in the car.

On an impractical note I think MOROSO used to make a thermometer that would screw in to one of the pipe threads on the intake manifold. You could verify the temp of that by using boiling water on the stove (keep in mind your elevation, that changes the boiling point of water).

Mike

[mockingbird812]

Thanks Mike, just what I was looking for. You are right, I want to make sure the gauge is reading close. So would it also be beneficial to hold the IR thermometer at 6" or less from the black electrical tape on the top of the thermostat housing? Also, are the radiator hoses (upper and lower) a good point to measure coolant temperature given their emissivity?

Your information is very beneficial as engine temps are critical to good reliable/non damaging operation. I will be giving a tutorial (with appropriate credit given) to all my friends that use these IR Thermometers as I think they have been mis-using theirs as I have.

[Dusk Blue Z]

Rubber works as an insulator, you can touch the hose when the engine is hot but you don’t want to touch the radiator shell which is down stream.

I took a look at your pictures, I wouldn’t put tape on the housing on that car. Just measure the thermostat housing with the thermometer close to it. The cooling wind from the fan and the built in error factor in your tester I don’t think will change your readings enough to worry about.

Mike

[mockingbird812]

Mike,

So because rubber is an insulator, does that mean it would not be a reliable place to take a measurement? Will take measurements on the sender housing per your instructions. Thanks!

[Kurt S]

I believe the standard place for measuring coolant temps with the IR gun is the thermostat housing.

For calibrating your gauge, just pull the sender unit out and put it in water. Measure the water temp with a thermometer. Compare.
Repeat with hotter water......