salty_waders

Ive seen a lot of posts about the accuracy of temp sending units, and of course a lot of posts about cooling problems. Most of them test the accuracy with an IR gun on the thermostat housing. This is what Ive been doing to test different sending units, and most have been 20-30 off. Someone pointed out that the most accurate engine temp should be read from the same area near the sending unit, not where the cooled water is entering the engine, which makes sense to me. So today I tested another sending unit that is supposed to be "calibrated" to be accurate. This time I measured the temp on the intake at the sending unit. The temp here is about 10* hotter than at the stat housing. The sending unit is accurate on my gauge within 5*, I can live with that! BTW I bought the sending unit from Corvette Clocks online.

midyearvette

thanks for the info...i think i will order a few, accurate ones are hard to find....

GCD1962

Buy an aftermarket temp gauge. Put the sender in one of the plugged holes on heads. attach a small wire with plug in to go to the gauge.
I made a box with three gauges for checking - water temp, tach and Vacuum. I can rest the box on the fender. It comes in handy when tuning the engine. When I'm finished I just disconnect them. With the aftermarket temp gauge you could even rest it temporarily inside the car when driving to verify the cars gauge.

Powershift

I discovered this a few years back, and that is why I always recommend "shooting the coolant temperature" at the sending unit boss in the intake manifold.

If you see a significant difference between the IR gun and the temperature gage, disconnect the sending unit wire and measure the ohms with a multi-meter. This will tell you if sending unit or gage (or wiring) is the problem.

Larry

JohnZ

There were no holes in the heads until 1968.

mikem350

The sending port is close to the thermostat housing, which is the where the hottest water ends up before going to the radiator...so these temps should be close.

Sometimes the gun reads off because of different surfaces and the way the beam bounces back. Keep shooting to see what makes sense..

GCD1962

Thanks John - I'll put that into my memory bank.

toddalin

And some read inaccurate because the surface you are shooting is too reflective, or ... Some guys paint the area to be shot in flat black.

When I shoot a pot of boiling water with mine, the reading is way off if I shoot toward the water surface, but accurate if I shoot the side of the pot. In this case, its probably a combination of things including the reflection, the moving water, the steam vapor, etc.

BTW, you should be able to determine the accuracy of your gun by shooting a pot of boiling water within a few seconds of turning off the flame. If you do it with the flame on, the pot is actually hotter than 212* so it needs a few seconds to transfer its heat to the water.