I've owned a couple 3800'*, so nothing strikes terror into my heart like the low coolant light. That quickly flashed on during a tight turn, so I pulled into a gas station and killed the engine. There was a little coolant in the tank, the radiator cap was cool (I didn't open it), and the upper hose was empty -- but the engine temperature was normal, and the heat was working normally.

Now, I don't have an oil milkshake nor condensation on my oil cap (LIM'* probably good), I have no white steam or smoke coming out of the tailpipe (UIM probably good), and my parking space is always bone dry (no leak) -- so where is that coolant going?

The last owner said he replaced the LIM gaskets, and there'* no loss of power like the Bonneville had when its UIM was starting to let go. At this point, I'm wondering if people are siphoning it out in the middle of the night.

Take a good look at the bottom of the throttle body and look for orange crust and also look at the weep hole on the water pump. It most likely is pushing a small amount of coolant at a time and while at operating temp causing it to evaporate. I've seen the LIM gaskets leak externally as well so take a good look at the head and intake areas for leakage. If the previous owner didn't replace the gaskets with the updated metal gaskets it'* quite possible they failed again.

Colin,
guess it is the LIM. Last owner states he replaced, but may not of replaced properly. Get a pressure tester on the cooling system and you will likely find the issue.

If it is loosing antifreeze, and not leaking on the ground or on passenger side floor, I'd be sure to replace both upper and lowers to make sure it was done right, then no need to worry about them for a long time

Also check for signs of a heater core failure.