Sorry for replying to an old thread. But I just did the LIM gasket and UIM swap on my 96 Regal with the 3800 series II. After getting it all back together, I filled the motor with coolant through the thermostat housing, drilled a small hole in the flange of the new thermostat, and filled the radiator. I bled as much air as is could after starting the car up, then I took her for a 15min test drive.

One thing I have noticed since doing this is the temp gauge used to stay consistently at the first mark on the temp gauge (i think i've read that this is 180 degrees) while cruising down the highway. Now, it will itermittently jump up to about 1/4 of the way above that first mark. Could this be due to the new thermostat? The old thermostat was a 195 degree one, and the new one is as well.

Could this be due to air still stuck in the system? I've tried to bleed it three times now, and all that seems to come out is coolant.

Any help would be greatly appreciated.

moved here from an old thread for better exposer and less confusion.

The problem is the hole. Even with a small hole, coolant gets threw and this causes problem regulating the temp. Filling the cooling system like you did, threw the thermostat opening, then putting the thermostat in and then fill the radiator is the best way. What I then do is put the cap on and squeeze the upper hose, this drives coolant back threw the thermostat driving out air. As long as you still have a 195*, the temp should settle in after the first open.

So, are you saying the hole I drilled in the thermostat flange is causing the small fluxuation in the running temp that I am experiencing? The old thermostat did not have this hole, so that may make sense. The instructions I found online said to drill the hole to help air escape the system.

I can live with this small fluxuation if it isn't causing any damage to the system. My main concern is if I still have air in the system.

There are some that say drill the hole. I say why change the way it'* made. It'* wont hurt your cooling system. But it could cause a problem in winter by over cooling and not letting the engine heat up fast enough, and this can cause a SES light on newer cars. I don't think it will be a issue on your 96. It'* more of a problem with 2000+

I see what you are saying about the hole not allowing the motor to heat up as well, since some coolant will pass through the drilled hole at all times. But that is the strange thing, the motor is now running HOTTER than before, but only slightly. It used to cruise right at the first mark of the temp gauge. Now it stays there most of the time but often jumps up to about a quarter of the ways above the first mark. It seems like the motor is running hotter. I guess I don't see how the hole in the thermo is making the engine hotter.

It'* probably running hotter because your old thermostat was stuck open, and the engine was running cooler. In other words, it would probably run even hotter if you put in a new 195 without the hole.

What he said. A new thermostat will open at the correct temp. I run a digital display in my car and I can clearly see a good 10* swing in temps as the stat opens and closes.

Cool, thanks for easing my mind guys. It definitely sounds like my old thermostat was stuck open. And if the first mark on the temp gauge is actually 180F, then it stands to reason that the needle would climb above that mark before the thermostat opens at 195F.

For the record, how would one tell if they have air in the cooling system?

check for bubbles in the coolant tank..if you dont have bubbles your air tight