2000 Bonneville not supercharged.

Not to sure what is happening. Have filled coolant reservoir and it drops by next day by at least a few inches but will maintain that level that it drops to. There are no coolant leaks that I can see, but the last few days I have been smelling coolant coming from under the hood. The temp gauge only goes up half way the same as it has always been and the radiator stays full. I also have a code p0507. Now after reading the posts I am getting nervous that it might be a UIM and possible LIM problem. I have not seen any white smoke coming from the tailpipe nor a sweet smell coming from there either. There is no sign of coolant in the oil. Is it possible that there is a coolant leak that is drying up from the heat of the motor? Oh yes when I do smell the coolant is after I have driven it for about a half hour. Any help would be most appreciated. Thank you.

Pull off the throttle body and look around the hole for the EGR. I'm willing to bet you will find coolant there.

Something doesn't make sense here..

You fill it and it then maintains the level after it "equalizes" itself to the same level as before. Are you overfilling the tank? When the coolant expands it does purge any additional that it doesn't need. This could be part of the smell.

You won't see a UIM failure in the oil btw, that'* a myth which is spread by people that don't understand the coolant fills the cylinder and not the oil passages. Only minute traces might slip past the rings and then it would be burned off by the heat in the crankcase.

Your best preventative maintenance is like Dan suggests pulling the TB (3 nuts) to double check that the UIM isn't coolant filled inside. Just odd that it equalizes itself then stays put. Usually you'd see it disappear a few times, then hydrolock. The LIM holds about a half gallon.

Thank you very much guys. I will look at that tonight.