Infrared Heat Gun Question

JayChicago

JayChicago

Well-known member
Below is a question I posted on the ChevyTalk site. Didn't get a satisfactory answer, so I'm posting it here. Cuz some of the smartest gearheads I know of are here on FordBarn. Anyone want to help answer this puzzle?


Violates the Laws of Physics

OK, 'splain this one to me:

Can't remember what thermostat I installed some years ago. So while engine is idling, I take a reading on the thermostat housing with a temperature gun, and it reads 180 degrees. I must have installed a 180* stat. Put the temperature gun on the radiator top tank next to upper hose, and it reads 190*. Maybe I used a 192* stat.

But wait a minute! How can the coolant get hotter as it moves away from the engine into the radiator? Where is the energy source making it get hotter? Violates physics!

Are these temperature guns sensitive to the color of the material it is aimed at? This is a SBC with aluminum intake and chromed thermostat housing. Radiator is painted black. Does the difference in color explain this? What am I missing here?
 
Yes, the guns are sensitive to the color, type and finish of surface the beam "lands on".
For instance, shiny surfaces like polished aluminum heads do not give an accurate reading.
Plus, you may also encounter different measurements on "heat soaked" surfaces like a radiator top tank.

Try taking a reading at the top finned portion of your radiator and compare it with the reading taken at the bottom of the radiator. Should be a difference that will indicate a cooling effect.

It all has to do with emmisivity.
Read about it here:
https://www.google.com/search?q=emm...i433j0i10l8.8401j0j4&sourceid=chrome&ie=UTF-8
 
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19Fordy said:
Yes, the guns are sensitive to the color, type and finish of surface the beam "lands on".
For instance, shiny surfaces like polished aluminum heads do not give an accurate reading.
Click to expand...

Good to know that. Thanks.
But that's disappointing. Means I can't necessarily believe my heat gun is giving an accurate temperature reading.
 
Just for the heck of it, take a reading on one of your ceiling A/C vents and compare it to what your thermostat shows. It's usually pretty close. Also, take readings on several painted or unpainted engine components like water pumps, intake manifold, exhaust manifolds, engine block and compare readings.
 
If you take a reading off a copper pipe and then where it changes to steel you will get several degrees difference and both those surface readings will differ from the actual temp.
 
What I have been told by an owner of a company that uses an Infrared gun to test heat accuracy in an industrial application that's critical. To test the guns accuracy they simply test it by using an ice cube. Should read 32 degrees. This might help to determine if your gun is accurate.
Ronnieroadster
 
A good while back I was researching which IR gun to buy. I found some of the better ones have a switch to select the type surface that is being measured.
 
Just spit balling: You said a SBC with a chromed T-stat housing/neck and a radiator. I'm assuming the following: T-stat housing was made from steel and the radiator had a brass tank.

Thinking back to physics class and if the gun is indeed accurate. Could it be the thickness of each part and the material make up of these parts (steel and brass) could show different readings due to the efficiency of the material's conductivity properties and the amount of heat they are able to release?

Brass is the better conductor of heat between the two materials and due to the thinner gauge of the tank vs. the housing, the brass tank is releasing the absorbed heat into the atmosphere more efficiently. Like 19Fordy mentioned in his post, it would fall under emmisivity

It would be even neater if we knew the temperature reading of the bottom tank after the water cycled through it.

Now I'm really curious about this...
 
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here are the results of some similar tests I did in 2014 :

"FYI, I did the same tests with the IR thermometer that you did. Here are the results :

......................Top of....Bottom.of..Front of......Back of.....Front of.......Back of
.....................Radiator..Radiator...Left Head...Left Head..Right Head...Right Head

Heater Off..........175.........157..........173......... ..175..........182............174
Heater On..........175.........174..........176.......... .177..........184............184

This was on a day when the outside temperatures were in the 70's and I run 180 thermostats. I am happy with these numbers. I find the differences in temperature interesting between having the heater "Off" or "On". This is a U.S. built car with the right head being the passenger side with the heater connections on it. It looks to me like the heater takes a lot of heat out of the system."
 
When testing steam and condensate systems in a factory we spray painted flat black on the spot we wanted to test.Ronnieroadster thanks for the ice cube idea.
 
Not sure that this applies to this discussion, but IR guns read only the very top surface. I test asphalt and the "correct" way to get the temperature is with a stem thermometer inserted into the hot asphalt as it is placed on the ground. Many people use IR guns, but as soon as the asphalt is rolled and the air blows over it, that top surface cools--maybe down to 150 degrees, but 1/16" into the mat. it is still 3100 degrees.
 
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