ah-kay. I will purchase the ir gun this weekend. I don't understand why I can't get a stable reading. The reviews of the one I have aren't bad.

Are you telling me if you hold the gun and point it next to the temp sender and keep the "scan" button pushed, you get a solid reading? Mine jumps around 10 + or 10 - C. It's black with oil in that area. I should be getting a solid reading. I'll try again...

Zeke. I don't mind that it's loud. Brooklyn is already loud.

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1984 300td euro turbo

No measurements yet as I am still at work. I am on PST time. Why don't you try this?

1) Tape a masking tape over the side of a pan and heat water until boiling.
2) Point your IR probe to it and it should read solid 100C.
3) Point to the stove, if electric, and get a reading.
4) When you point to the engine block, it has to be clean and non-reflective, as the laser works by absorption and reflection by the object.
4) You can also point to the top of the radiator which is matt finish and should give a steady ready. Or point to the sensor itself, tape a masking tape over it.
5) A dirty or oily service probably would not work.

You may not need a new probe, may be it is the battery.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

What, precisely, is the function of the laser portion of an infrared thermometer? Are you suggesting that the laser plays a role in temperature determination?

Yes.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

That would be the wrong answer. The laser is just a pointer; it plays no role in the temp determination. It makes no difference if the laser is reflected, absorbed, sliced or diced.

Aiming. The visible red laser is colinear with the IR detector.

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RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)