OT 1976 C10 low running temp on gauge

Courtland1949 · Feb 24, 2020

My 76 C 10, truck 250 engine is showing low temp on temp gauge even after a 1/2-1hour drive? I boiled the therm stat on the stove and it does open. Could the issue be with the gauge or the temp sending unit? Antifreeze level is full.
Temp reads between low and the next lower hash mark.

David G · Feb 24, 2020

Of course it opens when you boil it, but what temperature does it open at?

guido · Feb 24, 2020

Hello courtland1949,
. Just tap the ground side for a
If the thermostat was not opening, the engine would overheat. If it was stuck open it would not get very warm and you would have no heat if any.

One possibility is a bad sender. with the key on, have someone in the drivers seat, and while they watch the temp gauge, go from the sender to ground, and just tap the ground side.

If the gauge jumps up you found the problem. New sender will fix it,

guido.

guido · Feb 24, 2020

Hello courtland1949,

Not all gauges use the resistor, which is used for fine tuning the gauge. Theeft licture shows another resistor for calibrating thd gauge,

Guido.

Courtland1949 · Feb 24, 2020

My bad. I did not meas boil temp. But will do.

504 · Feb 24, 2020

My 97 2500 was running cool, after driving home from work the top hose was just warm. $13.00 later the hose is hot when I drive home.

Bob · Feb 24, 2020

(quoted from post at 21:25:40 02/24/20) My 76 C 10, truck 250 engine is showing low temp on temp gauge even after a 1/2-1hour drive? I boiled the therm stat on the stove and it does open. Could the issue be with the gauge or the temp sending unit? Antifreeze level is full.
Temp reads between low and the next lower hash mark.

Beg, borrow, buy, or steal an infrared thermometer and check the temperature on the cylinder head side of the thermostat housing, then you will know.

Oh, yeah, if I remember correctly the temp sender is screwed into the lower t-stat housing, that would be right where to check with a heat gun.

That being said, vehicle heat gauges are notoriously inaccurate, and don't get better with time.

If the measured temp is quite a bit different than the gauge temp, it could be a bad sender, or the wrong one for the application.

I've found that NOS genuine GM senders often tend to be a better match than the typical aftermarket sensor from a part store.

Also, having GOOD grounds between the engine, frame, chassis, and instrument panel makes the gauges more accurate.

Steve@Advance · Feb 24, 2020

Common for thermostats to fail in the slightly open position.

If the thermostat housing is cool enough to comfortably hold your hand on it,it is not coming up to temp.

Likely a new 195* thermostat will correct it.

jacksun65 · Feb 25, 2020

Put a piece of cardboard in front of radiator see if that helps.

caterpillar guy · Feb 25, 2020

And of course if the gage has been changed with a wet gage all those connection ideas can be thrown out the window. Would then be most likely the gage is bad. If the top hose is just warm might just be a circulation problem to the radiator. If the heater is just not getting hot then circulation to the heater is bad.

Courtland1949 · Feb 25, 2020

I did...still no change in temp.

Courtland1949 · Feb 25, 2020

W/key on and the temp sender wire grounded, the gauge jumped. Looks like a bad sender.

Thx all for your help.

used red MN · Feb 26, 2020

That?s easy, the boil temp was 212 degF lol! Unless you are up on Pikes Peak or something. But seriously, the general idea when testing a thermostat in heated water is to have a capable thermometer in the water at the same time to see at what temperature the thermostat begins to open. Then making sure that agrees with the spec of the stat. The test you did usually applies to a thermostat suspected of not opening at the spec temp which is usually below boiling point and then over heating the engine.

OT 1976 C10 low running temp on gauge

Courtland1949

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guido

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guido

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Courtland1949

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504

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Bob

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caterpillar guy

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