I'm at my wit'* end with this vehicle please help.....


136,000 miles.
Bought it from a bank it was a repo
Long story short I had to do head gaskets on it after I bought it because I was getting combustion gas in the cooling system and it would pressurise the cooling system with air and it would over heat. I had the heads milled, dipped, and tested for cracks. When getting the engine apart i had noticed that someone had already done the same thing that I was currently doing but they had used so much permatex on the intake that it completely blocked the cooling ports. I vaccumed the water jackets in the block to get out the sludge and flushed it. Currently it runs perfect but the cooling fans do not come on when it gets up to temperature. They also didn't come on prior to me doing head gaskets either. I have done and tested the following.

1. Changed the temp sensor. No change no trouble codes prior or after.
2. Unplug the temp sensor while the engine is running and at 220 degrees the fans come on and run at high speed until you plug the sensor back in then they turn off.
3. Using a scan tool I can turn the fans on and they run at high and low speed.
4. Fans run while using the air conditioning. But shut off as soon as you turn the AC off.
5. It may not be related but while using the scan tool I noticed that the PCM says that I have 133,444 miles on my buick. But my cluster says that I have 136,878. ?!?!?!?!?!?! Is it possible that my pcm was changed and not flashed could that be my issue. Or so I just have a possed demon vehicle. Aka Christine on my hands.
6. I have also read online that air pockets can cause this problem. I am 100% sure that I have bled all of the air out.

It appears that they are working correctly. We run into this occasionally with members here. Like the Bonneville'*, the fans won't turn on until 212 low speed and 226 for high speed. It could be that you are just not getting up to temp yet.

Put your scan tool back on and monitor temps at idle. Now, put a piece of cardboard in front of the radiator and continue to monitor the temps. They should go up, watch the temps on the scan tool, when the fan kicks on, that is your low temp turn on.

Agreed, you have confirmed that the PCM has the full ability to command and execute low and high speed fan runs, and can see what temperature the engine is. It is just refusing to do it.

As Mike said, it'* likely just not hot enough to turn the fans on yet. It would likely be good to reference a FSM to find out what the fan setpoints are, or let it push even hotter to force the fans on. I would expect 230*-240* to still be relatively safe, but beyond what the computer should allow, especially while supervised. I would intervene myself if approaching 250*. GM usually has 255*-260* marked for the critical overheat, where alarms and stuff start going off.

Agreed, ur fans are working properly.. Sometimes it also takes for the temp to get upwards of 230-32 before they would kick on. If ur temp guage is in normal operating temperture u have a more than healthy cooling system as long as its not over heating its no need to panic.. As far as the cluster and pcm having different miles. It could also be that the cluster has been swapped and no one matched the miles. Although it would be good to do. Some dont bother when the miles are so close together. Clusters often go wacky ive seem more than a few go bad on these things. So id run with the miles on the pcm.

Are you saying that the vehicle is still overheating?

What happens when you get the car up to normal operating temp(200F), and let the vehicle idle(block radiator like Mike suggested).....does temp rise into the red zone? Does fan come on before the red zone? If yes, at what temp? And what temp does it drop it down to? I would go by the temp readings of the scan tool, rather than by the temp gauge....

If temp rises towards red zone, and you are not getting heat out of your vents(blower high, full hot), there is possibly still an air pocket....