Just started 1 day ago. Even starting in the morning it already is @ 100 degrees cold. Runs up to 250 and gauge flashes hot. Seems ok. Cannot see the water pump weeping. Can it be the gauge sensor in the motor crapped out instantly? Heater core replace a few months ago, no problems their except it sucked putting it in.

Thank you

 

mine does that too, however it may actually be over heating for a second, because one time i turned the car on and watched the hose when it did it and the the in hose for the radiator (aka the engine out) crimped itself up. so i am thinking our problem actually might be the thermostat isn't opening until the heat get up there really high then it opens and cools down, mine will go all the way up once then drop and rest of time it is running it will be at a normal operating temp like 200. My dad also thinks it may be the thermostat, and he is a ASE master mechanic so Idk. btw, i am think i am using the right term when i am saying thermostat but now it seem like it might be wrong sp if it isn't i am meaning the component that opens up when the engine coolant temp reaches 190, or more like is supposed to open up.

 

I think you are on the right track with yours but mine is still different. It can sit all night and when I start it cold it will say it is 150 cold? I have driven it till it has pegged the heat guage and it is not getting hot. I am going to change the sensor in the block and or switch to a manual gauge. Everything else looks fine. Has to be the sensor or guage malfunction. If it would not show 150 in the mornings and go up to hot from there I would be more concerned on the thermostat scenario or pump issue. Thanks for telling me you issue.

 

does your gauge ever go under the temp you say it is reading at when it is cold. perhaps the gauge isn't adjusted correctly, i know my fuel gauge is off by like a cm. i don't know how instrument clusters work internally but would there be any way to adjust the hand over to the correct reading

 

I drove it one morning fine and then in the afternoon it went hot. Since then when cold it reads close to 150 every morning and climbs from there. It was not a teaser problem it just started one day and it is there now always. I knw it is not geting hotin the engine or it would have grenaded by now and does not smell or feel hot. If anyone knows if the electronic guage can be recalibrated that would be nice as this is a driver. Only has 126,000 on it. Take care, Thanks

 

do you have a haynes manual? if you do there is nifty little check procedure for the sending yunit which may be crappy out on your vehicle and thus sending inappropriate voltages to your temp gauge causing it to read incorrectly.

 

No but I could find one. Mechanic or libraries even carry them. Sounds odd to go to a library this day and age but hey. Better than changing tons of parts that do not fix anything.

Thanks

 

Mine kind of does the same thing (i think atleast ). I just finished rebuilding my 4.3 and got it running about a week ago. First test drive it got hot almost to the red, so I shut it down. Took it home and replaced the thermostat with a 190 degree. Gauge still read about 220 or 225 when warmed up. So I too figured must be a faulty sensor. Replaced that ($10) and still showed the same thing. Like your situation, the engine bay doesn't seem abnormally hot and I don't smell/see and coolant leaks. So I'm thinking it has to be the gauge.

I plan on adjusting the coolant/water ratio to a 30/70 sometime this week to see if that helps at all...

 

Hey thanks for this input. Some mornings the guage in this Blazer starts off close to 200 hundred and climbs to hot. Tis i what leads me to believe the sensor or guage. This morning it had no reading and ended up at its normal 210 - 220. All older Blazers w/ 4.3 seem to run 1 bar over 200 mark. I will probably change the engine snesor and also ad an underdash water temp guage. @ 126 thousand miles she is not pretty any more. Non of them held up body wise very well. Let me knowif the mixture helps.