75 vett temp gauge problem
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
75 vett temp gauge problem
My son has a 1975 Stingray and recently he has been having trouble with the temperature gauge. Most of the time it works as it should, however spiratically, the needle on the gauge drops all the way to the right just as if it was not getting any power or as if it was disconnected from the sending unit. Is this a problem with the gauge or the sending unit? I am not sure what the symptoms are when either go bad. Anyone have this expenrience before in the past? Thanks
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
My son has a 1975 Stingray and recently he has been having trouble with the temperature gauge. Most of the time it works as it should, however spiratically, the needle on the gauge drops all the way to the right just as if it was not getting any power or as if it was disconnected from the sending unit. Is this a problem with the gauge or the sending unit? I am not sure what the symptoms are when either go bad. Anyone have this expenrience before in the past? Thanks
The sender is on the driver's side of the block, indicated in the following image.
Reach down and disconnect the sender wire from the sender. Start the engine and check the gauge. If the gauge is working the needle should peg. Now, touch that wire terminal to a solid ground, and see if the gauge goes to zero.
If yes, the gauge is probably working fine. In that case, pull the sender from the block, clean the threads on both the block and the sender, install, and check again. If the reading is still erratic, replace the sender, and see how it reacts.
Last edited by Durango_Boy; Aug 4, 2008 at 04:17 PM.
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
The sender is on the driver's side of the block, indicated in the following image.
Reach down and disconnect the sender wire from the sender. Start the engine and check the gauge. If the gauge is working the needle should peg. Now, touch that wire terminal to a solid ground, and see if the gauge goes to zero.
If yes, the gauge is probably working fine. In that case, pull the sender from the block, clean the threads on both the block and the sender, install, and check again. If the reading is still erratic, replace the sender, and see how it reacts.
Reach down and disconnect the sender wire from the sender. Start the engine and check the gauge. If the gauge is working the needle should peg. Now, touch that wire terminal to a solid ground, and see if the gauge goes to zero.
If yes, the gauge is probably working fine. In that case, pull the sender from the block, clean the threads on both the block and the sender, install, and check again. If the reading is still erratic, replace the sender, and see how it reacts.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
Ok guys,
I have done the test by pulling the wire off the sending unit, but I was not able determine much. Reason is, when I first start the car with the engine cold, the temp gage is already pegged out on the hot side. Pulling the wire off the sending unit has no effect on the gage at all and the gage remains pegged. Once the car warms up, the gage will all of a sudden start working by immediately dropping down to the 190 degree mark. Any suggestions? Thanks
I have done the test by pulling the wire off the sending unit, but I was not able determine much. Reason is, when I first start the car with the engine cold, the temp gage is already pegged out on the hot side. Pulling the wire off the sending unit has no effect on the gage at all and the gage remains pegged. Once the car warms up, the gage will all of a sudden start working by immediately dropping down to the 190 degree mark. Any suggestions? Thanks
Burning Brakes
Joined: Oct 2006
Posts: 1,044
Likes: 0
From: Henrico VA
The sending unit is supposed to measure resistance I think. That sounds like you need a new sending unit, but ask one of the guys that knows. It is a very cheap part and the new one should be more accurate.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Ok guys,
I have done the test by pulling the wire off the sending unit, but I was not able determine much. Reason is, when I first start the car with the engine cold, the temp gage is already pegged out on the hot side. Pulling the wire off the sending unit has no effect on the gage at all and the gage remains pegged. Once the car warms up, the gage will all of a sudden start working by immediately dropping down to the 190 degree mark. Any suggestions? Thanks
I have done the test by pulling the wire off the sending unit, but I was not able determine much. Reason is, when I first start the car with the engine cold, the temp gage is already pegged out on the hot side. Pulling the wire off the sending unit has no effect on the gage at all and the gage remains pegged. Once the car warms up, the gage will all of a sudden start working by immediately dropping down to the 190 degree mark. Any suggestions? Thanks
The other side of that test is to touch the wire to the block or another part with a ground. It should peg the gauge at zero, opposite of a full bar peg.
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
I failed to put that in my post earlier today, but I did in fact do that part of the test as well. When the engine is cold, the gage pegs all the way past the hot mark and stays there. When I touch the terminal to ground, it has no effect on the gage. Due to this, I am thinking that I may have a gage problem or something other than the sending unit. Please advise me of your thoughts. thanks
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You don't have a gauge problem. You have a broken/frayed wire in the signal line or the connector and the wire are is not making good contact, or the sender wire on the back of the gauge is loose (not likely). Look very carefully at the connector on the wire going to the sender. Are the wires solidly attached to it? Could it be frayed/broken just inside the insulation? You have an "open" condition on the signal line that is intermittant....when it gets hot, it can sometimes make connection. Another 'test' would be to remove the connector from the sender, touch it to ground (ignition key ON but car not running), and wiggle the wire around to see if you can get it to make a connection.
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
You don't have a gauge problem. You have a broken/frayed wire in the signal line or the connector and the wire are is not making good contact, or the sender wire on the back of the gauge is loose (not likely). Look very carefully at the connector on the wire going to the sender. Are the wires solidly attached to it? Could it be frayed/broken just inside the insulation? You have an "open" condition on the signal line that is intermittant....when it gets hot, it can sometimes make connection. Another 'test' would be to remove the connector from the sender, touch it to ground (ignition key ON but car not running), and wiggle the wire around to see if you can get it to make a connection.
thanks again.
Thread Starter
Racer
Joined: Feb 2008
Posts: 357
Likes: 3
From: Madisonville Kentucky
You don't have a gauge problem. You have a broken/frayed wire in the signal line or the connector and the wire are is not making good contact, or the sender wire on the back of the gauge is loose (not likely). Look very carefully at the connector on the wire going to the sender. Are the wires solidly attached to it? Could it be frayed/broken just inside the insulation? You have an "open" condition on the signal line that is intermittant....when it gets hot, it can sometimes make connection. Another 'test' would be to remove the connector from the sender, touch it to ground (ignition key ON but car not running), and wiggle the wire around to see if you can get it to make a connection.
I checked the wire and the terminal connector, plus I traced the wire all the way back to the fire wall but did not find any bad sections. I had my son sit in the drivers seat while I tried touching the terminal to ground and wiggled the iwre but it made no difference, the gage stayed maxed out. The next thing to check I guess would be the connection on the back of the gage.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
It could still be the sender, but you indicated that the signal was intermittant. It would be very rare that a sender has that kind of problem; it's usually either OPEN or SHORTED. By any chance, does the sender have Teflon tape on it? If so, the tape could be acting like an insulator. The sender is supposed to be 'grounded' to the cylinder head. If the ground connection (sender threads) isn't making good contact, that could also be your problem.
