GLX

Details:.. I have a 1990 GT with 48K miles. Engine bay is spotless. Vehicle is totally stock. When the car warms up I have noticed that the temperature gauge rides at the 1/2 mark most of the time. During stop and go traffic it will go up slightly to beween the 1/2 and 3/4 mark. When I turn on the headlights the gauge starts to climb to the 3/4 mark and stays there. When warm I unplugged the sending unit and the gauge went to the cold mark. Turned on the lights and it didn't move. Checked the cooling sysem and it appears OK. I have all the receips from previous owner and he had the cooling system flushed out 3 years ago and replaced the radiator cap. The car shows no signs of overheating.
Any suggestions are greatly appreciated...Thanks for the help

mattdel

Sounds like normal gauge operation to me. I'd say you truly do have a mild overheating problem in stop-n-go.

The_Dude

With those miles, I'd say there's a good chance your radiator is plugged up. I'm sure it say for long periods without being flushed. Have you looked at the color of your antifreeze?

GLX

Yes the color is bright green...looks new. The previous owner had it flushed and filled in 2009 per his records that I got when i bought the car.
I just got back from a long ride city stop/go traffic, stand still in a construction zone, and freeway driving. Temp gauge stayed just above 1/2 way...The temperature gauge rises to the "R" mark when on the freeway at 2 -2500 RPM..Truly confusing..

9redfox3

Those Stock temperature gauges move all over the place I call it the dummy gauge ! Two things you can do. Install a new gauge or by a radiator cap temp gauge to see where you engine temp is at and compare the two?

GLX

@9Redfox3..Thanks! that's a great suggestion...never knew they made such an animal.......any idea where i can get one?

The_Dude

Mine runs anywhere from the middle to the top of the R. If you know your radiator is good, and there isn't any signs of overheating, don't worry about it. I had my radiator rodded out, and there wasn't any change. I'd prefer to see the gauge running below the middle, but the gauge doesn't appear to be calibrated that way. A new sending unit might make a difference. An easy test is, to get one of those infrared guns that tell you the temperature of whatever you point them at. There pretty cheap at the chain auto parts stores.

GLX

Tried installing a new sending unit today...Temperature is actually reading hotter than beore. Looks like it's time for some good aftermarket gauges...Any suggestions?

mattdel

Why are you so convinced the gauge is wrong? Your original post clearly indicates cooling system problems not at all related to gauge operation, likely fan clutch, water pump, or radiator.

GLX

Like my original post stated the temp gauge moves upward toward the "R" mark upon turning on the headlights. I was told that it its likely possible the sending unit was the cause. Tried to start with the simple remedy by changing it, that's why I did.