Bob Dylan once wrote, “You don’t need a weatherman to know which way the wind blows.

But for us car folks, there are plenty of times when you do need an accurate way to quickly measure temperature.

That’s when one of those digital infrared temperature guns can really be handy.

(Image/Jeff Smith)

What is a Digital Infrared Temperature Gun?

These useful, handheld temp guns are technically called non-contact temperature readers. These units use a laser pointer that is used to aim the gun toward the specific area to be measured. The tool’s actual measurement device is a lens that directs the infrared energy of the object onto a series of thermocouples that convert this energy into a voltage that is then calculated as a temperature. The result is a near-instantaneous surface temperature reading of the object.

This temperature gun has literally dozens of uses for automotive diagnostic work and even more beyond the automotive world. We’ve learned to use these devices to analyze how an engine or an automotive system operates without having to bother with the tedious work of mounting an internal sensor.

Most infrared guns scan a certain area based on the distance from the object to be tested. For the Milwaukee unit we used in this story, one foot away covers an area 1.5 inches in diameter. From three feet away the area is 3.6 inches in diameter and from five feet away the area is 6 inches in diameter. (Image/Milwaukee Tool)

As a quick example, we purchased a four cylinder Iron Duke powered S-10 pickup a few years ago that would eventually be fitted with a 355ci small block Chevy and a T-5 five-speed. The original four cylinder engine proved itself as a reliable but underpowered parts chaser. Its only problem was that it often overheated.

After a few early repair attempts with a new thermostat and clutch fan, we solved the problem by using our temp gun to measure the radiator temperature in four separate quadrants. The lower third of the radiator was nearly 80 degrees cooler than the top two-thirds, which indicated that the radiator was clogged with sediment and needed to be replaced.

The gun made the diagnosis and solution very simple.

How to Use a Digital Infrared Temperature Gun

milwaukee tool infrared temp gun and packaging
The Milwaukee infrared temp gun comes in this nice clear plastic packaging and includes the nine volt battery. (Image/Jeff Smith)

For this story, we’re using a Milwaukee infrared gun from Summit Racing (PN MWT-2267-20) that performs this exact same task. The gun is extremely easy to use and is powered by an ordinary nine volt battery that is included with the gun. Operation could not be simpler. Pull the trigger and aim the red laser beam at the object to be measured and the temperature will be displayed on the screen almost instantly.

This gun includes a user’s manual which can also be found online and even comes with the battery in the handle, though it still needs to be connected. To access the battery, turn the slotted screw head counterclockwise to unlock access the battery compartment in the handle. (Image/Jeff Smith)

You have your choice of Fahrenheit or Celsius readings and you have the option of holding the reading on the display. Other options include a minimum and maximum temperature range report if the gun is held on an object with the trigger pulled for an extended period of time. Milwaukee claims an accuracy of +/- 2 percent which is equal to +/- 2 degrees at 100 degrees F. This gun’s maximum temperature reading is 750 degrees F but there are other guns that can record higher temperatures of over 1,000 degrees F.

You also don’t have to worry about forgetting to turn the display off because it will automatically shut off after 10 seconds.

The Milwaukee display offers a ton of information as well as options to produce the results you desire. The only thing we did was specify readings in Fahrenheit. If the trigger is continually pulled, it will also display minimum and maximum temperatures. Plus, the display can be illuminated when working in areas with less light. We shot this photo taking the temp of our sodas in the shop refrigerator. (Image/Jeff Smith)

Things to Consider When Using an Infrared Thermometer

One trick we learned from a friend who is in the business of tool calibration is that infrared temp guns can become inaccurate when used on highly reflective surfaces. We’ve seen guns that are confused with highly polished surfaces like the top of an aluminum radiator and others that just seem to shrug off this issue.

Polished surfaces can cause accuracy problems with all infrared guns. If you need accurate results, just place a small length of normal masking or black electrical tape on the surface, allow the temperature to stabilize and then take the temp reading on the tape. (Image/Jeff Smith)

An explanation of this gets into the differences between something called surface emissivity versus radiated heat. We won’t bother with diving down that rabbit hole because there’s an easy work-around for this issue. The technique is to attach a short length of either black electrical tape or just normal masking tape to the surface.

Allow a moment or two for the tape to equalize temperature with the underlying component—like a polished radiator top—and the resulting temperature will be more accurate. According to the research we’ve looked at, the tape will generally be within +/- 2 percent. For most diagnostic purposes, this should be sufficiently accurate.

One of the best ways to quickly tell if an engine is suffering from a misfire is to point the gun on individual cylinders and look for one or more cylinders that are significantly colder than the rest. A dramatically colder temperature indicates a weak cylinder. (Image/Jeff Smith)

These infrared guns can be handy for a wide variety of uses. Keep scrolling and you’ll see a bunch of good ideas in the list at the bottom of this article.

But there are literally dozens more beyond automotive applications.

A quick way to evaluate power steering temperature after several laps in autocross or track days is to pull the cap and point the gun into the power steering fluid reservoir. We’ve seen power steering pumps fail due to high fluid temperatures exceeding 225 degrees F. (Image/Jeff Smith)

For example, you could impress your spouse by testing the actual temperature of your kitchen oven versus the temperature set on the dial. We use our gun around the shop anytime there’s an issue with temperature—with a half-second response time it’s a quick answer to the question:

“How hot is that?”

One way to quickly tell if your drag racing rear tire pressures will produce maximum traction is to check the tire temp across the face of the tire after a burnout. If the center temp is high, pressure is slightly high. If the middle temp is lower than the outers, then pressure is too low. (Image/Jeff Smith)

Popular Uses for a Handheld Infrared Temperature Gun Around the Garage

  • Measure individual cylinder exhaust temp
  • Radiator performance top to bottom on vertical flow
  • Coolant temp in and out of radiator (change in temp)
  • Supercharger discharge pipe temp
  • Turbocharger housing temp
  • Transmission sump temp
  • ATF temp in and out of trans cooler
  • Engine sump oil temp
  • Oil temp in and out of external engine oil cooler
  • Compare coolant temp to existing gauge reading
  • Power steering reservoir fluid temp after laps on track
  • Rear axle lube temp
  • Brake fluid or caliper temp
  • Heater and/or A/C discharge temp
  • Catalytic converter if plugged
  • Cabin floor temp test for possible insulation upgrade
  • Intercooler water reservoir temp
  • Alternator temp under load on hot day
  • Air cleaner body temp
  • Intake manifold runner temp
  • Fuel in float bowl after heat soak
  • Battery temp on hot days
  • Starter motor or solenoid temp
  • Shock absorber body temp after track use

Popular Uses for a Handheld Infrared Temperature Gun at the Track

  • Drag strip: Tire temp across tire after burnout
  • Autocross: Tire temp test across face for adjusting air pressure or camber angle
  • Autocross or drag racing: Track surface temp

Popular Uses for a Handheld Infrared Temperature Gun in an Industrial Shop

  • Check oven temp for powder coating
  • Temp of micrometers or subject for measurement accuracy
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.