55 temp gage mystery

[Roy B.]

Question! every time I first drive my 55 vett the temp gage goes to hot as the engine get warmed up then falls back to normal at 180, any one think they know why?? Been doing this for many years and the engine never gets hot.Thanks

[Gerard F.]

Re: 55 temp gage mystery

Maybe the thermostat has to warm up above 180 to fully open, then when it opens things cool down to the 180. Just a guess.

Jerry Fuccillo
#42179

[Les Jacobs]

Re: 55 temp gage mystery

Roy, If your temp circuit is wired like a 63, there's only a few things that can give a false "Hot" reading. A temp sensitive, sender , short in the sender wire circuit to ground, or a flakey gauge. First thing I would try(because its the easiest, and cheapest) would be to eliminate the sender - either by swapping it out, or thru the following test: Start with the engine cold, measure the resistance of sender. (the hot wire should be disconnected from the sender for this measurement) The resistance should be a several hundred ohms. Reconnect the temp sender hot wire. Let the engine warm up until you see the false Hot indication,(use an IR gun should confirm that the reading is false) and measure the resistance using the procedure as above. Continue warming up the car. When the gauge drops and starts reading correctly (midrange), measure the resistance again. If the senders resistance at false Hot, is lower than @ normal, then the sender has an intermittant problem. If the "false Hot" resistance is higher than the normal resistance, then the sender is not the bad actor. Good Luck Les

[Roy B.]

Re: 55 temp gage mystery

The thermostat is OK -I even used another gage and the sane thing happens- the gage is mechanical not electrical, like I said it's been doing this for years -the vett never gets hot. it just goes to hot , then in a second drops to normal. Must be a quirky thing on just my vett.
That's what I get for driving an old vett, should trade it off for a new 05 (NOT)

[Dennis C.]

Re: 55 temp gage mystery

Roy, I'd try Jerry's thought by pulling the thermostat to eliminate it from the picture temporarily and see how the temp gauge reacts. In the past, I've had temp gauges, that were very accurate, act like this. They were just telling the truth.

[Dick W.]

Re: 55 temp gage mystery

Roy, I had the same identical thing on a 89 Chevy PU. Would almost peg temp guage and then go to normal. Would only do it when you started engine cold. Replaced thermostat and problem went away. Apparently thermostat would hand closed and one it freed up it would work normal.

[Roy B.]

Re: 55 temp gage mystery Clark

I have the original bellow type thermostat in it , been in for 20 years . Clark! you may be right , I have a NOS one still in a box and I'll try it out. When did they remove using the bellow type unit ??

[Dennis C.]

Roy, Bellows type T/Stat went out of service...

...before I was born (1940)...

[Les Jacobs]

Re: 55 temp gage mystery Clark

Roy Suggest measuring the temp by the sensor to see what's really happening. Before getting the IR gun I used a meat thermometer when the wife wasn't looking with pretty good results. But I somehow justified the IR gun cost and now use it for "science" projects around the house.

[Gerard F.]

Re: 55 temp gage mystery

I keep one of those little aluminum meat thermometers taped to the radiator hose on my 67, just as a check on the temp gage. Finally bought my wife a new one.

Roy, if it's not broke, don't fix it.

Jerry Fuccillo
#42179

[Dave Suesz]