I have a 00 z28 (stock) and on long drives on the freeway usually an hour or so the temp goes whacko. It will go from like 209 to 230 in a seconds time and then go back down to the normal temp, it will do this within a few seconds of the last, and yesterday the temp went up to 260 in like 1 second then went back down to op temp, I even ran it with a/c, with heater full blast and just off no difference, I took it in to the chevy dealer and they said no thrown codes or ****, now I am out 100 bucks for them to tell me they dont ******* know?! I am taking it to infineon tomorrow, it did the same thing one time before I got to the track then it was fine. Can someone help?

 

probably could be a faulty ECT sensor that control the gauge.

 

Did you have any luck figuring out what is going on? My car is doing the same thing. it will be perfectly fine, running at 210, then all of a sudden it pegs the gauge, then comes right back down. will do it if i am sitting at a light or driving down the interstate. have changed the thermostat and coolent temp sensor and it seemed to help for a few weeks then it started up again. when it pegs the temp gauge i have looked under the hood, and nothing seems out of the ordinary, no steam or anything. still runs like a raped ape. just aggravating

 

put a new temp sensor in. Coolant can't rise and fall in 30-50 degrees in a matter of seconds, it takes minutes.

 

Thats because there is nothing going on, the temp sensor needs to be replaced.

http://www.rockauto.com/catalog/x,ca...,parttype,2188

 

Have already replaced the temp sensor. unless they need replaced every month

 

Then the wiring must be shorted somewhere along the line, or frayed. Or the guage cluster is messed up and the signal is getting screwed up.

 

I'm having the same issue. Any luck fixing yours yet??

 

Excluding the '98 year, all the gauges display a temperature reading of 210 degrees when the actual coolant temperature is between 180 to 226 degrees, once it rises above 226 the gauge will show the actual reading - making the temperature appear to rise and fall by a large margine in a matter of seconds.

 

same here, but mine actually did over heat to the point that it was shaking violently.

 

Sorry I don't get seem to get updates from this website, turns out it was a sticking thermostat.