Water Temp Gauge Issues

[jmscanlon2002]

Afternoon All,

I seem to have water temp gauge issues on my "new to me" 1979 Spider (automatic).

When I start the car the water temp gauge quickly (within 15 seconds) pegs out at 260.

I replaced the temp sensor.(the one in the block between the spark plugs) The same thing happened.

I bought a replacement (used) water temp gauge on eBay. This one seems to work fine.....

HOWEVER, when I turn on the lights the replacement gauge instantly pegs out at 260. I turn off the lights and
the gauge drops back to operating temp.

Any Ideas???

Any help is much appreciated.

Jim

[AriK]

Grounds grounds grounds and more grounds. Make sure the battery terminals are tight, the wire tight into the terminal, the other end into the battery box. Use a wrench, not just a visual. Check the ground pods on the front fenders in the engine compartment and another one under the dash. Cleaning all these points will prevent future gremlins such as this one.

[spider2081]

I think you have the same gauge as my 1981. I had a problem where my water temp would increase about 10 degrees with the lights on. I found the needle ground and the light ground are shared on the back of the instrument. I installed a separate ground wire for the light and that helped.
I believe you have two senders in the engine head. One is the over heat switch that pegs the needle, if the engine over heats. The other drives the needle. Do you have two senders and are you sure you changed the correct one.
The temperature sender decreases in resistance as the temperature goes up. I think it reads about 50 ohms to ground for 260 degrees indicated on the needle.
The warning sensor is a temperature controlled switch. It switches to ground and pegs the meter as a warning.
I would first inspect the wires for the sensors for any cracked or broken insulation.

[jmscanlon2002]

Thanks to those who replied.

I won't get a chance to check these suggestions out until the end of the week.

I'll let you know what happens.

[jmscanlon2002]

A special thanks to my 2 new best friends.

This was indeed a grounding issue.

I ran a new ground wire for the gauge and for the gauge lamp and now all is well........

Thanks again