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Hagerty Employee

Wrenchin' Wednesday: Using invisible light to find problems

Non-contact infrared thermometers, more colloquially known as IR temp guns, are incredible tools for diagnosing issues in your project. There's a few myths out there on how they work, but today we'll cut through the fog to show you how to use them and a little bit behind how these magic tools do their job.


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Pit Crew

Great tips. Have the Gun, but not the wherewithal to know these applications! thanks !



I have the gun, but so far have only measured some exhaust manifolds, and the inside of my mouth.  Oh, come on, you've all done it!

Pit Crew

I wish mine measured higher temps, it cuts off before it gets to brake rotor temp.


I miss the super-duper one I got to use on my factory automation-tech. days. Super accurate, could read bus terminals and breaker connectors easily, you could compare 3 phase 4160v fuses for a quick look for unbalanced legs. It had a much narrower beam/measurement spread. Can't remember the brand, probably Fluke or Snap-On. The Harbor Freight variety are fine to read most stuff, but you really get spoiled with a good one. 


The problem of the laser dot not perfectly aligning with where the IR is reading from is called parallax, and it will occur more strongly as one positions the reader closer.

You may be able to detect just how far off it is by using an incense stick or “punk”. It presents a very small, yet hot target. Hold it near and in front of a large plain background and engage the tool, pointing it at the lit tip until you get the max temp reading. The laser spot should show you the parallax difference.