Water Temp Gauge Pinning
My Friend has a 1966 Big Block (425HP) and after normal driving for approximately 10 minutes the water temp gauge is reading around 165 degrees (160 thermostat installed). All of a sudden the temp gauge pins all the way to the right approximately 3/4" from the 250 degree mark. The engine does not appear to be overheating as she seems to be running normal. He replaced the sending unit yesterday but the problem is still visible after 10 minutes of driving. The only Identification on the sending unit is the number 40; could this problem be the wrong sending unit or could it be the gauge itself? Any suggestions would be appreciated.
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Re: Water Temp Gauge Pinning
OK, I'm going to step out in the deep water. Eliminated the sending unit and if the gauge works it should keep working. I'll vote for the wiring somewhere rubbing and grounding the green wire to something. The wire from the sending unit on the motor is being grounded somewhere, somehow!
JR -
Re: Water Temp Gauge Pinning
Buy an IR temp reading gun; best investment I made. Picked one up at sears for about 40 buckeroos and man what a toy it turned into! You can measure the water temp coming from every outlet, etc.Comment
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Re: Water Temp Gauge Pinning
These symptoms can occur in one of two ways:
(1) The lead wire from the temp gauge to the engine compartment temp sender is shorting to ground intermittently.
(2) The temp gauge's native ground reference in the instrument cluster is sporadically opening up.
Few bother to understand/investigate #2. The gauge ground is accomplished via gauge to cluster wiring integrity, cluster to instrument panel mechanical attachment (screws), and instrument panel to dash harness wiring integrity.
Since you're only complaining of the temp gauge needle pegging and not other gauges doing squirrely things, I think you can believe the wiring harness to instrument panel integrity is good.Comment
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Re: Water Temp Gauge Pinning
I had a similiar problem on a 72 Monte Carlo. The temp circuitry is the same as the Corvette. I fought this for a long time with new senders, cleaning contacts, testing with a decade box resistor bank etc.
Finally decided to remove the gauge cluster itself and bench test the system. I found a bad ground on the gauge case to be the problem. It now works fine.Comment
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Re: Water Temp Gauge Pinning
If this is a intermittent problem, it may make this diagnosis more difficult.......Everyone is right on the money, so here's a step by step to help you fix it. This is how I would try to figure it out .......
1- Using a ohm-meter with alligator clips, connect one clip to the sender wire at the sender. Connect the other ohm-meter lead to a proper/clean ground.
2- Run the engine until you see the temp gauge "peg". Observe the ohm-meter. If it reads "zero" ohms(i.e. shorted), remove the green sender wire from the sender tab.
3-Touch the meter lead to the sender. If it reads "zero" ohms(i.e. shorted), the sender is bad(I doubt this will happen
).
4-Touch the meter lead to the green sender wire. If it reads "zero" ohms, then........
a.- wire is shorted to ground, or
b.- defective meter
5- While in above test mode, crawl under dash and carefully remove the connector at the temp gauge.
a.- If meter reads "open", gauge is shorted internally, or spade terminal insulator on gauge is shorted....
(IMO) Difficult fix.....pull gauge.
b.- If meter reads "short", the wire is shorted to ground between the sender end and the gauge connector end. If this is the case you will have to trace it through the harness to find it....
(IMO) Easy fix.
RichComment
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Re: Water Temp Gauge Pinning
Thank you all for your input/suggestions, I will pass it along to my friend.
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