Thread: Thermostat Always showing Hot

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Hello Hotrodders!

I have a 1978 Chevy K10 with a 1983 350. The problem is my thermostat always shows hot but the engine never over heats. The thermo has been changed out 3 times - twice by me. I have, also, changed the gauge. However they were not new gauges. Along with this the Temp seems to show properly when I shut off the engine leaving the power on. Along with that while the engine is engaged with the (MT) transmission the needles on all my instruments like to bounce a bit. When I put the clutch in the needles are static.

Easisest way to determine what the real temperature is would be to install a mechanical temp gauge.... The factory stuff is probably just plain worn out. Could be something as simple as a ground problem on the dash circuit. Wiring gets old and deteriorates, too.

Thanks for the reply Dave...

I hooked up another Factory Gauge from battery to Sensor - same thing. Note: the gauge rises slowly as the engine heats up. The grounding just pegs it. So I am sure that is not it. Do the factory gauges have a tendency to wear out? One gauge is new the other is original.

find some one with a mechanics temp gun that can verify the temp. My rad guy told me my guage read 30 degrees hotter than the engine actually was. where does you temp signal come from? if it is the head, do you have headers? or is your sender plugged into the intake? what degree stat are you running?

look for a cut or pinched wire under your dash and around your clutch pedal and linkage.

Originally Posted by tudorkeith

find some one with a mechanics temp gun that can verify the temp. My rad guy told me my guage read 30 degrees hotter than the engine actually was. where does you temp signal come from? if it is the head, do you have headers? or is your sender plugged into the intake? what degree stat are you running?

I do have headers - They are coming off while I do a rebuild. Signal ( sending unit ) is inbetween 1 and 3.
I believe it is a 180.

Originally Posted by 53 Willys

look for a cut or pinched wire under your dash and around your clutch pedal and linkage.

I as going to do that next. I just bought this truck and the wiring is a mess under the dash. But that said I hooked up a second Gauge directly to the battery and got the same result.

You mention changing gauges, but have you changed the sending unit? In my experience the sending unit is the piece that sees the thermal cycles and goes bad. The gauges, provided the wiring is sound and ground is good, last lots longer.

Originally Posted by TMA1

I do have headers - They are coming off while I do a rebuild. Signal ( sending unit ) is inbetween 1 and 3.
I believe it is a 180.

Maybe I'm wrong but you meat your sending unit is between 1 and3 right. and seperatly you have a 180 stat? did your wire from the sending unit touch the header and melt the insulation?

Originally Posted by rspears

You mention changing gauges, but have you changed the sending unit? In my experience the sending unit is the piece that sees the thermal cycles and goes bad. The gauges, provided the wiring is sound and ground is good, last lots longer.

I have changed it twice and the guy before at least once.
I am seriously considering Mech gauges.

Originally Posted by tudorkeith

Maybe I'm wrong but you meat your sending unit is between 1 and3 right. and seperatly you have a 180 stat? did your wire from the sending unit touch the header and melt the insulation?

No , however the original path of the sensor wiring was behind the engine then back up and around on the drivers side. I cut that wire off short and run it right in front of the brake power booster. Practically a straight shot to the sensor.

I mentioned earlier I was seriously considering mech Gauges. Are they difficult to install? What are the best connection components?
What do I do about the Oil light? :