"Engine" Temperature Measurement.

[mockingbird812]

I need some input from some of the sage experts . I need to know a reliable and consistent method to confirm the temp of the engine coolant using an IR temp gun. I made some assumptions that:

1. GM knows where to place its temp sender unit to provide the best pickup point for measuring the coolant temperature at it pertains to monitoring engine operations.

2. When using an IR gun, you should measure at the same point on the engine as GM does (at the temp sending unit) in order to cooroborate the temp gauge (aftermarket mounted under the dash) read out.

What I noticed was that I have approximately three different IR temp readouts when taking measurements at the base, middle, and top (at wire lead) of the stock temp sending unit. The lowest temperature was at the base and the highest at the top. The range was approximately 22 degrees.

I am using a "Mannix" Infrared Thermometer (model # IRT2) which has a laser pointer built in. I stand approximately 3 to 4 feet from the intended point of measurement. Temperatures were recorded from a '69 L78 engine built to stock specifications.

Thanks!

[Dusk Blue Z]

Sam,

I use these in my line of work (Predictive Maintenance) I’ll try and explain the short version of how they work and how you can get different readings from them. All the Infrared units work off a diverging cone starting from the sending unit, the farther you are from the source the bigger the area you will be measuring. You could get the specs on your tool but a circle of 12” over a distance of 10’ would not be unreasonable. The laser pointer will just show the center of the circle. Try and change your distance to the target and see if the temperatures don’t change as well.

Any temperature measurements that you get from the surface of an object are radiated readings. Different colors radiate heat differently; there is a reason that radiator’s and race motors are painted black. Materials will also have an effect on the radiation of heat.

Thinking of the temperature differences of your sensor, your lower reading is reading the casting and sensor, the middle reading will be mostly sensor and the top reading could be the black Bakelite material and the background surface.

If you were to use Thermography to capture a thermal image of your engine you would need to have some point of reference to determine what the actual temperatures of the different colors and materials would be. In industrial electrical applications we use a piece of black electrical tape as our reference point.

There are a lot of areas where Thermography could help to solve some problems in automotive applications. I have heard that some NASCAR teams have used it to look at their tires surface temperature during test sessions.

Not so short an answer, but hope it helps.

Mike

[YENKO DEUCE REGISTRY]

Interesting, ya learn something every day!

[mockingbird812]

Good info Mike. Thanks for taking the time. In practical terms how do I determine if my temp gauge is providing accurate information? I.e. what procedure can I use to measure my coolant temp with the IR thermometer?

Specs on my Mannix IRT2 are
Optical ratio 6:1
Resolution 1 degree
Emissivity 0.95
Accuracy +/- 3% or +/- 3deg. C

Instructions state that "Not recommended for measuring on shiny surfaces. The smaller the target, the closer the unit should be to it."

The sticker on the side of the thermometer has a diagram depicting the 6:1 Distance to Spot Size ratio. Is this spot the area of temperature measurement? I.e at 600mm or about 2 feet (from gun to measured surface) the area of measurement is 100mm or ~4 inches.

[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!