Temp gauge vs. IR Gun

[richard5933]

Going from Milwaukee to Gillette WY this past week I noticed the temp gauge moving past its usual spot. Up till now, it's hovered just a hair above the 180 mark on the gauge at about 185. During this trip it was hotter and the needle as where I'd guess 190 would be if the gauge was marked better. On some grades the temp rose a bit more, perhaps to 195.

At a rest stop I took out the IR gun to see how accurate the gauge was. While the gauge was reading about 185 (and running) I aimed the red dots at various points around the thermostat housing and the base of the different temp sensors. The highest temp I could find with the IR gun was 165.

How much differential is there between the actual coolant temp inside the housing vs. the temp as read with the IR gun externally at the housing?

I doubt the engine was running at 165, but I couldn't find anywhere external with higher readings.

[luvrbus]

Depends on the gun the cheaper ones are not very accurate ,you need one that has a emissivity control different metals and colors affect the cheaper one, and you need a good distance to spot ratio too but they are expensive.I have checked the H/F gun with water and candy thermo in a pan of boiling water and it was off 22 degrees brand new, your gauges maybe more accurate than your gun, just saying   

[chessie4905]

How do you know the candy thermometer is accurate? Does water bowl at 212? where you live? Don't know what your altitude is there. Yes, if you are going to get an Ir gun, it pays to get a good accurate one.
Might be time to install those misters.
What was the outside temps that day? Might be hotter out than you realized.

[eagle19952]

How do you know the candy thermometer is accurate? Does water bowl at 212? where you live?

Daniel Gabriel Fahrenheit pretty much figured it out.

One can heat something in the oven and calibrate/verify the HF gun.

[buswarrior]

The engine temp has changed as you took the load off, got it off the highway, parked, and walked back to engine room with the IR gun.

Seen too many posts recently with this sort of measuring strategy.

On the MCI with the floor hatch down the back, an assistant can shoot the pipes heading for the stock HVAC in real time. Put some heat on, so there is coolant flow...

Yup, your gauges might be wrong, your IR gun might be wrong, your methodology might be wrong...

This is the big time, get out yer ca$h, education doesn't come cheap...

Happy coaching!
Buswarrior

[Iceni John]

Do you have a quarter-sweep or a full-sweep gauge?   The latter has three times the resolution of a quarter-sweep gauge, making it much easier to read the actual temperature.   Accuracy is something else, but a good quality gauge with a stepper motor drive can be very close to 100% accurate.   I always test my temperature gauges in boiling water before installing them, and any that are more than a few degrees off go back for exchange.   All this is useless if the wiring between sender and gauge has resistance, so that's another thing to check and if necessary replace.   I like the Speedhut gauges, made in USA, custom faces and colors, very accurate, and less than $80 for a 2-1/16" temperature gauge.

My cheapo HF temperature gun gives a very rough approximation at best, and it's difficult to get several consistent readings, especially against shiny surfaces.   My Extech 730 clamp-on ammeter has a thermocouple, and it's more accurate than the HF gun!   Nothing beats a trustworthy good-quality temperature gauge, especially if you have a 2-stroke.

John

[DominicM]

I work as a coating inspector and use analog thermometers and the IR gun.  Both instruments need to be calibrated and checked frequently.  The IR guns are far more inaccurate especially at hotter temps.   I do use the IR but as a general reference. Once the temp is getting hot and I want a more accurate temp I have a surface temp gauge.

To calibrate take multiple gauges, ideally one that is a known or certified to be correct, and then use all gauges on the same surfaces hot and cold( boiling and freezing are both known temps). 

I have bought 10 HF IR guns just to find 3 that were reading accurate at 3 feet. The rest were anywhere from 10-25% OFF.( yes they were junk)

[luvrbus]

Actually water boils here at 212.165 F ,the thermometer was on the money with the oven and the microwave probe and my Fluke 568 agreed ,cheap IR guns you get what you pay for, I need good a gun when checking EGT the H/F crap is what it is.  next question   

[richard5933]

All good information so far, but not exactly what I was asking.

Assuming that the IR gun is accurate - what should be the temp differential between the gauge temp (which is measuring the coolant fluid inside the housing) and the external of the housing where the gauge sensor is mounted?

When I did the test, the temp on the gauge was holding steady at 185. The temp on the external of the housing was reading 165 with the IR gun. My assumption is that the exterior of the house, being exposed to the air, will be somewhat cooler than the coolant inside. I just wanted to find out how much.

For information's sake, the dash gauge is factory. It it quarter sweep marked in 40-degree increments from 100 degrees to 260 degrees. On most of this trip it read just above the 180 mark at what I would approximate to be 185. On steep/longer grades it went to about 195, perhaps as high as 200 for a few minutes. No higher. Entire cooling system and engine are bone stock.

[chessie4905]

How hot was it outside the coach at the time? Time for misters if you've seen 200. Radiator clean? My ir gun is a Raytech. Got it before hf started selling them. Richard, compare your gun temp accuracy by pointing it at boiling water and the side of the pan the water is in.

[luvrbus]

The water freeze plugs read the same as the water temp inside and the block will to after it heat soaks ,a winter time test will confirm that.If you worried about the housing not reading the same you have the thin crossover pipe and other places to get a reading from 
   

[richard5933]

Curious regarding the external temps, I got three of these from Amazon. They all read slightly lower than the 165 F that the infrared gun showed.

Not sure what the actual temp internal is, though the gauge shows about 185-195 when operating in summer. I've got an appointment next week with Luke for routine maintenance, and I plan to ask him to verify accuracy of gauge.

[chessie4905]

Read the bare brass of the temp sensor and then around it.
They make temp discs that are attached to cylinder heads to indicate overheat. Used by engine rebuilders. Don't know if you can get them rated at 200, 205, or 210°. Might be useful when you happen to run uncomfortably hot.