coolant gauge always hot
Thread Starter
Intermediate
Joined: Oct 2014
Posts: 44
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coolant gauge always hot
Hi everyone wondering if anyone has come across this before, my 81 coolant gauge is always pinned on hot whether the car is running or not, when I turn the key to the on position it moves very little more to the hot side but its always way passed hot, has anyone come across this problem before? or can anyone post a wiring diagram of how the gauge is wired and where its wired to or what would pin it to hot? im guessing its a wiring problem cause the rest of the gauges seem to work fine, any help is much appreciated thanks
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Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
A bad sensor or shorted wire shouldn't peg the gauge with the key off. From reading his question, it sounds to me like it is always hot, then when he turns the key on it moves further to peg. That's the way I read it. If it only reads hot with the key on, the sensor or wire is a possibility, but not with it off.
Pull the wire off the sensor and see if your gauge drops down, if not, maybe a gauge issue. I have no experience with an ECM, so I can't answer the other question.
Pull the wire off the sensor and see if your gauge drops down, if not, maybe a gauge issue. I have no experience with an ECM, so I can't answer the other question.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
A gauge that is 'pegged' with the key ON will also be 'pegged' with the key OFF. The reason that it is 'pegged' is that there is a fault in the wire...most likely at the joint with the connector that attaches to the sending unit.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
When he turns the key on, it moves higher. (according to his original post), If the sensor wire is shorted, I don't see that happening. Either way he can eliminate the sensor and wire by disconnecting the gauge and see if it's still hot. I hope he comes back with the fix for his problem.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
There is absolutely NO reason to get into the gauge to diagnose the OP's problem. If the gauge moves when the key is turned ON, then the gauge is not at fault (it either works or it doesn't).
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
There is absolutely NO reason to get into the gauge to diagnose the OP's problem. If the gauge moves when the key is turned ON, then the gauge is not at fault (it either works or it doesn't).
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Melting Slicks
Joined: Jun 2014
Posts: 2,236
Likes: 498
From: NJ
There is absolutely NO reason to get into the gauge to diagnose the OP's problem. If the gauge moves when the key is turned ON, then the gauge is not at fault (it either works or it doesn't).
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Since the gauge is functioning, the OP merely needs to remove the wire from the sending unit. Then, with ignition ON (engine not running), the OP can make two simple checks:
1) with sender wire removed (open circuit), the gauge should read at the high end of the scale;
2) with sender wire grounded to block (or any metal that is connected to chassis electrical 'ground'), the gauge should read at low end of scale.
Simple as that. If Test #2 fails (stays at high end of scale), the sender wire has an OPEN circuit....likely at the connection for the sender. If Test #2 passes, but the gauge still reads high, the sender is defective (it could already have an 'open circuit' inside).
Willcox (CF Vendor) has all this documented on his [Diagnostic] web pages. Good things to review BEFORE digging into the gauge cluster area.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You are correct, 1Hotrodz. I rechecked the Willcox site and grounding the sending wire will send gauge 'high'; open circuit will read 'low'.
The tests are the same but the responses are just reversed. In any event, you still DO NOT need to dig into the cluster to diagnose your problem...and the problem is NOT the gauge. Either the wire or the sender, as I indicated in my first post.
Good luck with your testing.
The tests are the same but the responses are just reversed. In any event, you still DO NOT need to dig into the cluster to diagnose your problem...and the problem is NOT the gauge. Either the wire or the sender, as I indicated in my first post.
Good luck with your testing.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
You are correct, 1Hotrodz. I rechecked the Willcox site and grounding the sending wire will send gauge 'high'; open circuit will read 'low'.
The tests are the same but the responses are just reversed. In any event, you still DO NOT need to dig into the cluster to diagnose your problem...and the problem is NOT the gauge. Either the wire or the sender, as I indicated in my first post.
Good luck with your testing.
The tests are the same but the responses are just reversed. In any event, you still DO NOT need to dig into the cluster to diagnose your problem...and the problem is NOT the gauge. Either the wire or the sender, as I indicated in my first post.
Good luck with your testing.
I don't know if you noticed or not, but the original guy has posted a new thread saying he didn't get anything from this one?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Hi everyone wondering if anyone has come across this before, my 81 coolant gauge is always pinned on hot whether the car is running or not, when I turn the key to the on position it moves very little more to the hot side but its always way passed hot, has anyone come across this problem before? or can anyone post a wiring diagram of how the gauge is wired and where its wired to or what would pin it to hot? im guessing its a wiring problem cause the rest of the gauges seem to work fine, any help is much appreciated thanks
Temperature Gauge, will read like this with a blown resistor
Temperature Gauge, will read like this with the resistance (ohms) wire grounded out 1968-1982
I've not read above due to time constraints this morning.... but pull the wire off the sending unit with the key on and see if the gauge goes back to cool. If not, and based solely on the fact the car is a 1977-1982 I would pull the cluster and check the PCB connector in the center of the dash.
The fingers on the board have a history of coming loose and touching each other. This could be your issue. I know the video below is for a 1968-1976 but it works exactly the same for the 68-76 cars.
If you wish to know how to bench test the gauge use these inputs.
Testing a 68-76 Temperature Gauge -or- What your non working gauge can tell you!
65-67
68-76
Last edited by Willcox Corvette; Mar 27, 2015 at 07:58 AM.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
You were probably thinking of the fuel gauge circuit which is exactly the opposite. 
The best way to keep this sorted...
When ohms is missing from a gauge, it always goes to what you want the most.
Temp gauge = cool
Fuel gauge = full
Oil pressure = maxed
Oil temp = cool.
and it's just the opposite for each gauge when they are grounded out.
Can the needles slip on the gauges... Highly unlikely. Gauges that appear inaccurate are usually this way from faulty input or they have been calibrated wrong since new.
The needles are press fit and they can be pretty hard to remove at times. We use a cocktail fork that has been specially bent to remove the small gauge needles. The only time we remove the needle is if we are replacing a face (really no need now since the cost of a new gauge is cheaper then the labor and the face) or if the gauge is just no accurate and needs to be re-set.
The best way to keep this sorted... When ohms is missing from a gauge, it always goes to what you want the most.
Temp gauge = cool
Fuel gauge = full
Oil pressure = maxed
Oil temp = cool.
and it's just the opposite for each gauge when they are grounded out.
Can the needles slip on the gauges... Highly unlikely. Gauges that appear inaccurate are usually this way from faulty input or they have been calibrated wrong since new.
The needles are press fit and they can be pretty hard to remove at times. We use a cocktail fork that has been specially bent to remove the small gauge needles. The only time we remove the needle is if we are replacing a face (really no need now since the cost of a new gauge is cheaper then the labor and the face) or if the gauge is just no accurate and needs to be re-set.
Last edited by Willcox Corvette; Mar 27, 2015 at 08:07 AM.
Thread Starter
Intermediate
Joined: Oct 2014
Posts: 44
Likes: 0
hey everyone, I pulled the connector off of the sensor and the gauge stays where it is, the new gauge that I put in did come already in the hot position, im going by the picture that is on Wilcox website that shows exactly where my needle is sitting which says I have grounded ohms, with the key on or key off or running the needle does not change it always on hot and when you turn the key on the needle moves slightly, I will start checking the wiring and I will repost with anything I find