Temperature Gauge Issue

[TR4]

I started my TR4 from its winter sleep and the temperature gauge ran up to 100 C so I pulled out my infrared temp gauge and at the thermostat housing, it read 150 F. The car idles fine and revs great. No hissing after I turned off the motor. Is there a resistor that I need to check and where would I find that? Could the gauge itself be bad? It does reset after the engine cools down. Maybe the thermostat is not opening? All advice to help correct this issue will be greatly appreciated.

 

[DrEntropy]

The gauge should have a regulated 10V on the supply side. If it's higher than that you have a faulty voltage regulator.

 

[TR4]

Thanks, that's easily replaced. Additional information, when the car is idling, the gauge rests around 80C but when I rev it up the needle quickly goes to 100C but the infrared thermometer continues to show 150F at the thermostat housing when revving. Funny thing, the gas guage now seems to be operating properly where it was quite erradic last season.

 

[KVH]

It could certainly be the sensor, but on my old TR4, whenever the gauges would act up, I'd check that little Voltage Stablizer under the dash, to the far right on the side wall.

Your temp gauge connects right to it. I went through two Voltage Stabilizers, so I know they can fail. On mine, the "give away" was that my fuel gauge was also acting up. Both rely on that Voltage Stabilizer as I recall.

I think they're fairly cheap to buy. You might explore that if no other solution appears at hand--and especially if you have had any short circuits lately.

I know folks all have different experiences, but I've never had the sensor, itself, go bad.

 

[roofman]

I just installed one of the elecronic voltage stabilizers often found on ebay. I had the same 2 guages acting up and now they work fine. It seems those 2 guages often act up at the same time when the stabilizer is bad.

 

[Geo Hahn]

I've had a sensor fail but that caused the temp to read too low. My only voltage stabilizer failure casued both gas and temp to read low.

If you measure for that 10V output from the stabilzer use an analog meter (needle/dial) and not a digital as it is a dirty sort of 10V. I think it is just bouncing between 0 volts and 13 volts in a fashion that tries to average 10V.

 

[roofman]

You are right it is the gas and temp guage affected by the voltage stabilizer. Memory failed me.

 

[DrEntropy]

Thanks, that's easily replaced. Additional information, when the car is idling, the gauge rests around 80C but when I rev it up the needle quickly goes to 100C but the infrared thermometer continues to show 150F at the thermostat housing when revving. Funny thing, the gas guage now seems to be operating properly where it was quite erradic last season.

You may have two seperate issues: Stabiliser faulty causing the gauge to read higher as RPM's (and a resultant voltage increase) rise, and a seperate issue with the gas gauge circuit... likely a resistance somewhere due to corrosion on connectors or the sender. Check the stabiliser first (and George's analog meter comment is right on target), then with that issue out of the way proceed to the gas gauge anomaly.

 

[TR4]

Thanks to all who replied, I changed the voltage stabilizer and the temp and gas guages both are operating properly while running the motor in the garage. I just need to wait for nice weather to take the car out of hibernation. Supposed to be 65 and sunny this coming Saturday. Keeping my fingers crossed. Thanks again !!!!!