[Normy]

Dueller, I'd still think bad thermostat. It isn't unknown for thermostats to be bad from the factory. Get another one and put it in a pot of boiling water, watch what it does. If it works [the wax pellet melts and the sealing plate moves] then pull it out and install it.

Two points from 928-land that have some pertinence:

1. The 928 CANNOT run without its thermostat. Without a thermostat, a 928 will overheat in a hurry! That is because the t-stat on a 928 not only opens a passage to the radiator, it also blocks a bypass passage. I don't know if the gm 3.5 is like this, but it is something to consider.

2. Some replacement 928 water pumps have plastic impellers. This is because the earlier metal impellers were known to occasionally shift and grind into the soft aluminum block. The fix? Plastic. The problem? The plastic impeller would occasionally come loose from the metal shaft and the car would mysteriously overheat. I wonder if that can happen to this V6? Unfortunately, the only way to find out if this is the case is to pull the water pump.

Best of luck-

N