78 temp gauge on cold
Thread Starter
Intermediate
Joined: Jul 2022
Posts: 25
Likes: 0
From: Missouri
78 temp gauge on cold
Hi everyone. I just bought my first Corvette. It's a 1978 automatic. As I was driving it I noticed the temp gauge stayed on cold. Never got into the normal range. Could this just be the thermostat needing to be replaced? I'm not a mechanic by any means but I think I could replace the thermostat if that's all it is.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Not likely thermo.
If the needle pegs, that's usually a poor GRD.
If the needle is inactive, I believe that is a poor power source. Either no voltage or low voltage.
I believe all the gauges are on one fuse. So are the others working?
If the needle pegs, that's usually a poor GRD.
If the needle is inactive, I believe that is a poor power source. Either no voltage or low voltage.
I believe all the gauges are on one fuse. So are the others working?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Ok. Using the numerical order of the cylinders, your coolant temp sender is located between cyls #6 & 8 on the passenger side.
Or, between #1 & #3 on the drivers side. Previous owners may have moved it to either cyl head.
Should be a single brown wire going to the sender. The sender is threaded into the cyl head. A single connector or blade is on the tip of the sender.
The reason only one wire is needed which is positive is because head itself is the GRD or negative, completing the circuit.
What happens is, with the sender in either location the sender is directly under a valve cover gasket. The gasket leaks, oil drips down on the senders terminal rendering a complete circuit questionable at best.
In some cases the wire simply falls off. Sometimes its burned from the exhaust. And often its just a poor connection from oil.
Try some carb cleaner sprayed inside the terminal and wire brush the senders brass blade.
Should be good to go when you start the engine. If not, electrical testing is in order.
Or, between #1 & #3 on the drivers side. Previous owners may have moved it to either cyl head.
Should be a single brown wire going to the sender. The sender is threaded into the cyl head. A single connector or blade is on the tip of the sender.
The reason only one wire is needed which is positive is because head itself is the GRD or negative, completing the circuit.
What happens is, with the sender in either location the sender is directly under a valve cover gasket. The gasket leaks, oil drips down on the senders terminal rendering a complete circuit questionable at best.
In some cases the wire simply falls off. Sometimes its burned from the exhaust. And often its just a poor connection from oil.
Try some carb cleaner sprayed inside the terminal and wire brush the senders brass blade.
Should be good to go when you start the engine. If not, electrical testing is in order.
Le Mans Master
Joined: Jun 2019
Posts: 7,650
Likes: 2,466
From: Indiana
you are getting great advice…
take pics of areas and post them..
follow wires under..
more the merrier
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Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Mine on my 78 w/ Aluminum heads reads low too. As I understand these gauges are not linear so could be accurate at certain points on the gauge. My gauge does move to the top 200? and goes back down when I get out of traffic.
Burning Brakes
Joined: Dec 2021
Posts: 805
Likes: 260
Hi everyone. I just bought my first Corvette. It's a 1978 automatic. As I was driving it I noticed the temp gauge stayed on cold. Never got into the normal range. Could this just be the thermostat needing to be replaced? I'm not a mechanic by any means but I think I could replace the thermostat if that's all it is.