Temperature guage on the fritz as usual

Hello all...I am trying to get to the bottom of this and after pouring over a heckuva lotta posts about overheating and such I'm scratching my head on my problem. Twoo weeks ago or so my temperature guage went into the red. I pulled over added some dex-cool and it went down to normal (half way ) op range. A few days later it started running hot again so I took it in and needed the intake maifold replaced. Took care of that, the temp guage went back to 1/4 range to a half...two days later it shoots straight back into the red....and pins there....i took it back in..they hooked it up to the computer and the computer said the engine was operating at 195 degrees....my gauage read in the red....so they switched the sensor....it went back down to the 1/4 mark and 1/2 mark on the temperature gauge....now two days later the temperature guage is behaving badly again...it operated in the 1/4 to halfway mark for one day...now today it pinned at the half way mark for one of my trips....this afternoon its creeped to the 3/4 mark and pinned there....the interesting thing is it never goes back to zero like it used to when the engine is shut down....(at least i think it used to go to zero when i shut it down, its been behaving oddly so much I've lost track),,,anyone have any ideas....?

Update...this morning I turned on the van and it ran up to the 3/4 mark and pinned there......i parked the car and the guage pinned at the 3/4 mark...i turned the engine off and it went doen about 3 ticks...i turned the ignition key off and on again and it went down three more ticks, i did it two more times and it went to zero finally...10 minutes ago i drove it and it pinned just below the red and is stuck there......chevy custoner service called me up last night and said they never heard of something like this happening before....:banghead:

Are both your cooling fans kicking on when the needle hits 1/2 and above. They should. Did you have the thermostat at least replaced when you did the intake gasket. Although I assume that the old coolant was not reused when they did your intake, please confirm. Did they pressure test or at least flush out your radiator? Did they check for any coolant in the oil, are you blowing any white smoke (vapor) leading to a possible head gasket leak as well? No other coolant leaks anywhere? Near the water pump or at hoses crossing behind your front three spark plugs, or at the hoses above and behind your t-stat?

..they hooked it up to the computer and the computer said the engine was operating at 195 degrees....my gauage read in the red....anyone have any ideas....?
The temperature gauge moves based on a signal from the PCM (computer) that is sent to the instrument panel, and then goes through a processor there (it is NOT a direct reading from the sensor).

Also, the fans will not turn on until the temperature of the coolant reaches about 225 degrees. This will probably only happen if you are NOT moving while the engine is running for some time (like parked or stuck in traffic).

I suspect that there is a problem in the instrument panel, possibly the gauge itself, or the connection to it. When you turned the key on and off multiple times and got different readings, that says (to me) there is an electronic problem.

Let us know what happens.

Take Care,

Hello all, I'm about to go get this thing checked one more time. But in answer to your questions, the fans work, the pressure test came back fine, there's no leaks anywhere (external!), the over flow is full, the thermostat was not changed just the temperature sensor, no white smoke or vapor, i still do the trick with the guage by turning the key on and off to reset it to zero for fun and giggles.....will keep you informed

Unless the shop tested the t-stat and said it was good, I would have replaced it when they did the intake manifold gasket. Just replacing the t-stat may run you about $300 US now since it may have to be done separately. Usually a full overflow means bad t-stat or other blockage, major air in system, etc. I would bleed both (hose at t-stat housing, and bleeder screw near water pump to make sure that that is not your problem.

Unless the shop tested the t-stat and said it was good, I would have replaced it when they did the intake manifold gasket. Just replacing the t-stat may run you about $300 US now since it may have to be done separately. Usually a full overflow means bad t-stat or other blockage, major air in system, etc. I would bleed both (hose at t-stat housing, and bleeder screw near water pump to make sure that that is not your problem.
:crying:
I'ved had the same problem with my temp gauge and my speedomoter. Flip the ignition several times at a stopped possition and it all returns to normal most times. Does this mean it needs a new computer?:runaround:

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