59 Temp gauge problem

[67vet]

The temperature gauge on my 1959 Corvette goes from 0 deg to 220 (full) in 30 to 40 seconds.
I changed the thermostat and checked for correct operation in a pot of boiling water.
I put in a new water temperature sensor on the intake manifold.
I used a handheld temperature sensing gun on different areas of the engine. Never got above 170 on the radiator, 160 at the radiator hoses or 140 at the thermostat housing or the water temp sensor.
I disconnected the wire from the water temp sensor and the gauge goes to zero.
Do I have a ground problem? :confused

Roger

 

[Tom Bryant]

Possibly. You need to have clean threads for the sensor and use no Teflon tape or any type of pipe sealer to ensure a good ground between the sensor and the engine. The brass of the sensor is soft enough to conform to the threads of the hole and seal well.

Tom

 

[LLC5]

The temperature gauge on my 1959 Corvette goes from 0 deg to 220 (full) in 30 to 40 seconds.
I changed the thermostat and checked for correct operation in a pot of boiling water.
I put in a new water temperature sensor on the intake manifold.
I used a handheld temperature sensing gun on different areas of the engine. Never got above 170 on the radiator, 160 at the radiator hoses or 140 at the thermostat housing or the water temp sensor.
I disconnected the wire from the water temp sensor and the gauge goes to zero.
Do I have a ground problem? :confused

Roger

Make sure that you have the correct sending unit for your vehicle. The sending unit that is in your manifold could possibly be for a idiot light in the dash, which is basically just a grounding on/off switch for the light. Good luck with it.

 

[Bwmurph]

Don't do what I did: Installed the new temp gauge in my '59, started the car let it warm up and got no reading on the gauge. Tapped on the guage and the needle moved a little bit; tapped on the guage a little harder and the needle moved a little more; tapped on the guage pretty hard and BOOM ! The temp sending unit in the manifold exploded and imbedded itself in the ceiling of my garage !! Good thing the hood was up or it would have gone right through it.

Turns out when I was tightening the wires on the back of the gauage I tightened one a bit too much and the pin on the back of the guage grounded out against the side of the guage creating a dead short. When I tapped on the guage hard enough I guess it sent enough current to the sending unit to explode it. I'm still thankful I didn't have a friend with me who might have been leaning over the motor and gotten really hurt (or worse) and that I didn't blow a hole in the hood.

Just something else to keep in mind>

Bernie O.

 

[67vet]

Update info: no change - still get full 220 reading after less than a minute.
The original water temp sensor worked fine until one day it didn't.
I cleaned the threads and used a dental tool to check the theads in the manifold. All cleaned up, reinstalled both the original and then the new water temp sensor and still the same results. :confused
The gauge returns to zero as soon as the wire is removed from the water temp sensor. Any further advice would be appreciated.

Roger

 

[Silver Blue 58]

Roger,
Does the ST-12 have anything on troubleshooting?? I am not near my resources (lakehouse).

Might be ground or guage.

Fred

 

[cbernhardt]

Temp gauge

Roger:

The original GM temp/ohm curve is as follows.
160F-140ohms
170F-125ohms
180F-110ohms
190F-100ohms
200F-87ohms
210F-75ohms

With the engine warmed up, engine off but switch on, does the gauge still read 220?

The temp gauge receives power from a pink wire from the fuse block and the ground is through the temp sensor. You should first check the voltage at the gauge (pink wire) and also check the resistance to ground at the gauge end of the blue wire from the temp sensor.

Try running a new (temporary) wire from the gauge to the temp sensor. Could be that the original wire is grounding somewhere when the engine warms up.

Charles

 

[JohnZ]

Simple check for wiring and gauge function - with the engine off and the key "on", remove the connector from the sending unit; the gauge should peg to full cold. Then ground the connector to the engine, and the gauge should peg to full hot.

 

[67vet]

Charles,
I ran the engine again and waited until the temp gauge read 220. As usual it ran up to 220 within a minute.
I turned the ignition switch off and then to on. The gauge rose to 180 then to about 185 and stopped. I started the engine and the gauge rose right up to 220. I did this a few times and had the same results.

Might be a short, what do you think? I sure hope I don't have to crawl under the dash to the gauge.

Say hey to Carol for me.

Roger

 

[67vet]

JohnZ, I performed the checks that you suggested:

Simple check for wiring and gauge function - with the engine off and the key "on", remove the connector from the sending unit; the gauge should peg to full cold. Then ground the connector to the engine, and the gauge should peg to full hot.

Results were as you suggested. Thanks

Roger

 

[cbernhardt]

Temp Gauge

Roger:

What happens if (engine cold) you just turn the key on (do not start engine) and leave it on for a few minutes?

Sounds like your gauge is working properly, just getting wrong grounding signal. Do you have an OHM meter?

Charles

 

[67vet]

Charles,
I turned the key on with cold engine for a few minutes. The gauge did not move. Yes, I have an ohm meter, but have not used it yet.

Roger

 

[67vet]

Charles – and everyone else who has been helping me with my temperature gauge problem –
With the engine running, I checked the voltage between the water temperature sensor and the blue wire that attaches to it. I found the voltage to be 15.5 volts.
Then I checked the ohms between the top of the water temperature sensor and ground.
Initially with the engine cold the reading was about 165 ohms. As the engine warmed up it went as low as 125 ohms. At that point the IR temp reader showed 170 degrees at the front of the manifold where the heater hose outlet is.
The ohm meter then remained fairly steady at 140 ohms, suggesting the thermostat was doing its’ job.
That is about all I can check at this time. My right shoulder is somewhat locked up and I can’t do any dash diving right now to check the gauge or wires. Any more thoughts or suggestions would be appreciated.
Thanks

 

[JohnZ]

Charles – and everyone else who has been helping me with my temperature gauge problem –
With the engine running, I checked the voltage between the water temperature sensor and the blue wire that attaches to it. I found the voltage to be 15.5 volts.
Then I checked the ohms between the top of the water temperature sensor and ground.
Initially with the engine cold the reading was about 165 ohms. As the engine warmed up it went as low as 125 ohms. At that point the IR temp reader showed 170 degrees at the front of the manifold where the heater hose outlet is.
The ohm meter then remained fairly steady at 140 ohms, suggesting the thermostat was doing its’ job.
That is about all I can check at this time. My right shoulder is somewhat locked up and I can’t do any dash diving right now to check the gauge or wires. Any more thoughts or suggestions would be appreciated.
Thanks

That suggests excessive charging voltage, which will definitely affect the temp gauge reading. To verify, put your voltmeter leads across the battery terminals with the engine off; it should read 12.4-12.6 volts for a fully-charged battery. Now repeat, with the engine running at about 1200-1500 rpm; it should read 13.5-14.2 volts. If it reads 15.5 volts, the voltage regulator needs attention.

 

[cbernhardt]

Temp Gauge

Roger:

Well for one thing your charging system should not be outputting 15.8 volts. The shop manual says 13.8-14.8 volts. Was the engine at idle while you were taking the readings?

I don't know if the excess voltage would cause that much of a difference in the temp gauge readings. The temp gauge is basically an amp meter so, using the basic V=I*R formula, a 190 deg reading at 100 ohms and 12 volts means 12v = I * 100ohms, or I(current)=0.12amps. At 15.8 volts, 15.8v = I * 100ohms, or current = 0.158 amps. So if the gauge is simply an ammeter, the gauge should read higher with a higher applied voltage. Whether it is enough to cause the gauge to peg that quickly is another question, I doubt it would be. I guess you could check it by warming the engine up till the gauge reads 220 then cut the engine off and turn the switch back on and check the temp gauge reading with the engine not running. Also check the voltage with the engine off.

edit: I see JohnZ beat me to it.
Here is info from the 55 shop manual: http://chevy.oldcarmanualproject.com/shop/1955/55csm06y07.html

Charles

 

[67vet]

Thanks John Z and Charles. I'll get my wife, Pat to work the accerator and read the RPM's tomorrow.
Sure sounds like you have isolated the problem.
When I took the reading the engine was at idle.

Roger

 

[cbernhardt]

Voltage Regulator

Roger:

If you should determine that the excessive voltage is the cause of your problem and you open up the voltage regulator, be sure to check the points for corrosion/oxidation. The problem may just be that one (or more) of the the points are stuck together. Even if they are not stuck, they should be cleaned with a fine file or emory paper.

Even if the excessive voltage is not causing your temp gauge problem, you need to correct it.

Charles

 

[paul robb]

I have a 66 vette with the same problem. after four years of trying to get the gauge to work right, new gauge, three new senders three repair shops, I gave up. I installed a digital temp gauge under the glove box, problem solved. I sure would like to to have this gauge working properly so if anyone can solve this I would like to here from them.

 

[67vet]

I decided to order a new voltage regulator. It should arrive later this week. Since I have to move/remove the generator I think I might as well change it out.
I'll post the results after I do the swap out.
Roger

 

[67vet]

Today I removed and replaced the original voltage regulator with a new one. The bad news is that I still have the same problem.
Later today I was told of a possible fix. I wonder if anyone else has heard that a resistor in line with the blue wire to the water temp sensor might fix the problem -- E = I X R.
Isn't if fun to try and track down the cause to a problem.