Theoretically, the air will work itself out of the system as the coolant cycles through expansion and contraction cycles. When this happens, you will see the level of coolant fall in the recovery tank as it is drawn into the engine as the coolant contracts. You will then notice the temperature gauge swing less widely as the thermostat opens and closes. But, sometimes, this doesn't work all that well.

Some rev the engine to about 2k briefly a few times with the car'* front end on an incline to encourage trapped air to escape through the bleeder. Ever since I got a huge bubble trapped in a '97 SSEi, I use a complicated method of filling the engine with coolant that minimizes any air getting trapped in the first place. It is documented here: http://www.bonnevilleclub.com/forum/...=article&k=100

I think that your un-drilled thermostat will add to the problem of bleeding the system. I thought I read here recently where the newest GM thermostats include a bleeder valve. Better late than never. http://www.bonnevilleclub.com/forum/...ic.php?t=89905

I know this is an old thread, but I'm having the same issues with a 195* thermostat constantly flucuating between 160* and 195* and never settling on a constant temp.

Is that complicated coolant filling method documented anywhere on the site now?

Funny that the thermostat I took out when I bought the car was stuck open, but did have the bleeder ball valve on it. The NAPA one I installed didn't have any valve or holes.

I'm to the point of paying the $$ for a new GM 195* thermostat.

One thi8ng you can try is to drill a 1/8 hole in the thermostat to allow coolant to flow threw even if closed. What this does is prevents air from being trapped below the thremostat. Personally I have never had this problem on any of my installs.

I no longer drill holes and the one time I had air trapped, the holes didn't do a thing.

You may find that filling slowly and using the valve on the thermostat housing help. Running the car a bit and letting it cool, then checking the radiator again.

If that fails, try car ramps to raise the front of the car. When that fails..drain out some coolant and then refill. As odd as it sounds this may free up some trapped air.

Little experience modding the 3.8, but have owned 4 cars with them and a lot of miles racked on each. They all seemed to fluctuate regardless of thermostat used, as if the radiator works so efficiently that the thermostat cant keep it at a constant temp. From the get go, number 1 3800 liked to sit at 205, (fluctuating as the thermostat opened/closed) by the gauge, and dealer mechanic said they were a 195 thermostat and the gauges arent real accurate and the engines were designed to run hotter. That was in 87. Through the years they all acted this way and I just assumed it was the way it was to be. Running under pressure with the sufficient force the water pump delivers, I highly doubt air is trapped anywhere. It'* a supposition and I think a false one. If your coolant reservoir is filling/draining normally then how could air be a problem? If it isn't then wouldn't the relief valve in the cap itself is faulty? Isnt the PCM involved in the engine temp? Wont it try to fend off any changes? Very curious of all this.

The only thing the PCM will control is the turning on and off of the fan. And this is mainly when stopped. Mine moves around a bit as well. Perhaps if I have time I'll run a scan and record the temp changes and post it.