. Temp gauge vs. infrared heat gun

[66hcs-conv]

Hi All,

I got one of the Mr. Gasket temp/radiator caps, and comparing the cap to an infrared heat gun the cap is reading 20 degrees warmer than the heat gun. The gun is being "aimed" at the tstat housing and/or the top radiator hose where it enters the radiator. Gun is showing 182 and the temp gauge is reading 200. Temp gauge in the car is exactly 1/2 way - pointing straight down.

Not sure which one to believe, although the gun seems closer to reality.

Are the gauges that far off?

Dave

 

[robert campbell]

Dave,
Use a candy thermometer or a like type to measure temp. Ensure that the water level is a couple inches lower than the fill cap. Start car with cap off and watch it warm up. When thermostat opens the water will rise, but should not flow out. Note water temp and gauge in car when it opens and starts flowing. This will give a baseline for your inside gauge. And the temp that the thermostat opens.

The problem with the cap style thermometer is if the water level is a bit low it measures the temperature of the steam vice the water. Kinda like what happens when you shut your engine off when hot. The temperature sender is high in the manifold and will get a air bubble and read very hot when the water temp is not as high. Although a hot engine shut off will show a spike in temp right off the bat.

Rob

 

[66hcs-conv]

Rob, thanks for the information.

So who makes a quality, accurate, temp gauge, that can be installed in the car, 'prolly under the dash, and where does its sending unit mount?

Thanks, Dave

 

[robert campbell]

I have Autometer "phantom" gauges in my GNS. Sending unit goes right where the original is. so you should unhook your stock gauge to use it. And in my opinion that sucks.

I would take readings with the cap open and even use you infrared gun and watch the stock gauge. I have found the stock gauge to be very reliable and once you know that 1/2 way is say 190 degrees, you can estimate either way from 1/2 way.

Just my two cents. I redid my entire dash with the Autometer gauges. And installed them in my Shelby console.

 

[p51]

To get an idea of how accurate your IR thermometer gun is I'd suggest doing what Rob suggested about measuring the coolant temp with a thermometer. Once the thermostat opens up take a measurement at the t-stat housing with your IR thermometer and compare that to the temp you're getting directly from the coolant. I would suspect that they should be close (not sure just how close, however). Try not to take temperature reading with the IR thermometer on reflective surfaces and hold the gun as close to the surface as is safe.

Regarding where to hook up a new temp gauge. Well in my case my thermostat housing had place for a thermally activated distributor vacuum control valve (see link) which I was not using with my Edelbrock carb. I put my new gauge sending unit where the original was and put the original sending unit where the vacuum control valve was. The new gauge measures the temp of the engine. The old original gauge measures the temp on the radiator side, so it's not accurate until the thermostat actually opens. One side benefit of this is if your thermostat ever sticks closed you'll know because the two gauges will measure very different temps even after the engine has warmed up.

http://www.mustangbarn.com/images/vacs/68 f37.jpg