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Old 08-14-2012, 07:00 PM
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IR temp vs. coolant temp

My gauge is not reading correctly in my car. It's a Classic Instruments gauge. They say 9 times out of ten if it's not reading correct it's a ground issue... but I've tried everything with no changes.
What I'm wondering.... is an IR temp gun reading going to be fairly similiar to what the actual coolant temp is? I realize it varies with where you point it.
When my car is at it's hottest (after 10mph for a mile in 115 degree heat with the AC on) guage reads around 230-235, the hottest part as read by the IR gun on the motor is the top radiator tank at about 212-213. Lower tank is more like 195 or so. Hitting the manifold where the temp sending unit is is always much lower... maybe 175 or so.

Basically.. the highest temp registered by the IR gun is always about 20 degrees cooler than the gauge temp.
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Old 08-14-2012, 07:12 PM
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check the emisitivity of your camera and adjust to what you are reading if you have the ability to adjust this you should be able to read fairly accurate temperatures.
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Old 08-14-2012, 07:45 PM
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If you're not able to adjust emissivity, (most laser temp guns don't have the capabilities of a high dollar thermal/IR camera), putting a strip of black electrical tape on the object being targeted will give you good reflectivity and better reading, but that's going to extremes IMO.
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Old 08-15-2012, 06:21 PM
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If you boiled a pan of water on the stove. Removed it when it came to a hard boil and shot the side of the pan with the IR gun. Would that not give you a comparative reading to check the accuracy of the gun with. You know the water will be at 212 degrees when it boils. Just thinking out loud here.

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Old 08-16-2012, 10:10 AM
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I don't have an issue with what the IR gun is reading. I believe it's correct. It's the cars temp gauge that's wrong. What I was asking is with the IR gun pointed at the top radiator tank, the temp reading should be pretty right on to what the coolant temp is, correct?
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Old 08-16-2012, 02:00 PM
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In a modern car probably but in a street rod there may be an expansion tank full of air in the top of the radiator. Be sure you are testing an area that is full of coolant and not air. Also, test the thermostat housing. It will give you the temp the coolant is leaving the engine.

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Old 08-18-2012, 11:26 PM
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Low voltage to the gages will also cause a high temp reading.
(you got 14v with the car running???)
Low voltage---less resistance---higher reading.

Might get with the instrument manufacurer and see if you can get
the specs on the temp sender.

certain resistance values will equal certain values on the gage.

If you have any idea what these values are----you can narrow down the
culprit.

IF you have a VDO sending unit, you may get away with calling Dakota Digital.

They once gave me the specs, but I have long since misplaced them.
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