TQ: Intermittent Temp Sender Failure?
06-14-2016, 01:31 PM
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TQ: Intermittent Temp Sender Failure?
NOT Corvette... but Corvette related. 
I put a new VDO 250* temp gauge in my 37 Chevy. I also installed a new VDO 250* sender. Life was good. Everything worked fine,
UNTIL... I got back from vacation. The car had sat for about 3 weeks. Started the car... the gauge went to 150* and then fell back below the 100* mark. Wouldn't move as the car warmed up. On several subsequent starts with a cold engine -------> same thing.
On subsequent starts with a warm engine, the gauge stays at 100* and won't move.
SO, I grounded the sender wire... and the gauge pegs to 250*. That tells me that the wiring and the gauge itself are OK.
I've fooled with a lot of temp senders in my day, and they either work or they don't work. I've never run across one that failed like this one is doing.
I ordered a new sender from VDO, but have a hard time believing that the one in the car would fail after ~2 months.
Thoughts?
TIA.
Chuck
PS: The car DOES have a 327 motor, and ALL 327 motors are Corvette motors.
I put a new VDO 250* temp gauge in my 37 Chevy. I also installed a new VDO 250* sender. Life was good. Everything worked fine,
UNTIL... I got back from vacation. The car had sat for about 3 weeks. Started the car... the gauge went to 150* and then fell back below the 100* mark. Wouldn't move as the car warmed up. On several subsequent starts with a cold engine -------> same thing.
On subsequent starts with a warm engine, the gauge stays at 100* and won't move.
SO, I grounded the sender wire... and the gauge pegs to 250*. That tells me that the wiring and the gauge itself are OK.
I've fooled with a lot of temp senders in my day, and they either work or they don't work. I've never run across one that failed like this one is doing.
I ordered a new sender from VDO, but have a hard time believing that the one in the car would fail after ~2 months.
Thoughts?
TIA.
Chuck
PS: The car DOES have a 327 motor, and ALL 327 motors are Corvette motors.
06-14-2016, 01:44 PM
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Assumming there is enough coolant flow reaching the sender, ground the body of the sender (to check that it is properly grounded through the threads - I have never seen one that had this condition, but......).
I have a "resistor box" that I can bring over and we can check the circuit, plus put on an ohm meter to check resistance change at the sender (when cold and hot).
Welcome back.
John
I have a "resistor box" that I can bring over and we can check the circuit, plus put on an ohm meter to check resistance change at the sender (when cold and hot).
Welcome back.
John
Last edited by Plasticman; 06-14-2016 at 01:45 PM.
06-14-2016, 02:51 PM
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Assumming there is enough coolant flow reaching the sender, ground the body of the sender (to check that it is properly grounded through the threads - I have never seen one that had this condition, but......).
I have a "resistor box" that I can bring over and we can check the circuit, plus put on an ohm meter to check resistance change at the sender (when cold and hot).
Welcome back.
John
I have a "resistor box" that I can bring over and we can check the circuit, plus put on an ohm meter to check resistance change at the sender (when cold and hot).
Welcome back.
John
Hard to believe I'd "lose" a ground on a sender that has been installed for 2+ months.
So, I put a 3/4" box wrench on it and bopped it about another 1/4 turn. We'll see what shakes out. And no, I never put teflon tape or thread sealer on sender units.
John is going to stop over later this afternoon with some of his electrical test equipment to check things out.
Yep, John lives about 1.5 miles from me as the crow flies.
06-14-2016, 04:48 PM
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Problem is that the sender is threaded into an aluminum sender block, sandwiched between the intake manifold and the thermostat housing, and it has gaskets (that are also electrical insulators) on top & bottom.
Therefore the only path to ground is through the stud shafts, from the thermostat housing, through the sender block, and into the intake. Chuck needs to add a ground strap from one of the nuts on a through stud (or elsewhere on the engine) to that aluminum sender block. Otherwise, he is relying on minimal (if any) electrical contact between those studs and the sender block.
John (Plasticman)
Therefore the only path to ground is through the stud shafts, from the thermostat housing, through the sender block, and into the intake. Chuck needs to add a ground strap from one of the nuts on a through stud (or elsewhere on the engine) to that aluminum sender block. Otherwise, he is relying on minimal (if any) electrical contact between those studs and the sender block.
John (Plasticman)
Last edited by Plasticman; 06-14-2016 at 04:50 PM.
06-14-2016, 05:01 PM
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Problem is that the sender is threaded into an aluminum sender block, sandwiched between the intake manifold and the thermostat housing, and it has gaskets (that are also electrical insulators) on top & bottom.
Therefore the only path to ground is through the stud shafts, from the thermostat housing, through the sender block, and into the intake. Chuck needs to add a ground strap from one of the nuts on a through stud (or elsewhere on the engine) to that aluminum sender block. Otherwise, he is relying on minimal (if any) electrical contact between those studs and the sender block.
John (Plasticman)
Therefore the only path to ground is through the stud shafts, from the thermostat housing, through the sender block, and into the intake. Chuck needs to add a ground strap from one of the nuts on a through stud (or elsewhere on the engine) to that aluminum sender block. Otherwise, he is relying on minimal (if any) electrical contact between those studs and the sender block.
John (Plasticman)
I still find it odd that it worked for 2 months... THEN this "issue" arises.