Water temp gauge issue.

[jwldane]

Hi.

I have search the threads on the site and can't seem to get an answer to my issue.

My temp gauge is pegged at HOT. As soon as I turn the key to the acc position it pegs.
The gauge was working perfectly before I messed with the thermostat. I had an overheating problem and replaced the thermostat with one from Vicks. Could never get the lower radiator hose to get hot and the car would eventually overheat and overflow the reservoir.

Put the old thermostat back on this morning after boiling it to make sure it opened. It does. My lower hose it now getting hot as it should.

Problem is my temp gauge now pegs at hot all the time. Is it possible I fried the overtemp sensor so that it is in a constant state of over temperature? Could I have fried the needle sweep sensor or maybe both? Could I have fried the gauge? I have tried removing both sensor wires at the head (one at a time) with no change. Wiring is in same position as it was when the gauge worked.

Is there a way to bench test each sensor?
Can I bench test the gauge?
Can I run a temporary direct wire from the sensor to the back of the gauge?

The car is a Frankenstien car made from many parts cars. 2 liter block with 1.8 liter head. I have a green wire leading to sensor between spark plugs 1 and 2 (close to radiator) and a grey/black wire leading to sensor between plugs 2 and 3. I believe the wiring harness is from an older model. I cannot see or find any secondary resistor under the dash, however I have one in a parts bin that came with the car. Gauge has green wire, black/yellow wire, white wire and black and white wire at the back.

Any help or suggestions are greatly appreciated. Thanks.

[GeorgeT]

I would pull the wire on the over-temp sensor to see if the gauge still pegs. If not, you have a bad sensor, ift it still pegs you have a short somewhere.

[spider2081]

If you remove both wires from their sensors in the head the gauge needle should be pointing full to the left. if that is the case connect just the green/white wire to its sensor and inspect the ground on the grounding pod above the ignition switch under the dash.