Cadillac Repair: 1999 cadillac deville overheating......, coolant level, engine coolant

Question
I have a question regarding my 99 Cadillac Deville...Driving on the freeway, i sped up to pass a car in my lane and thats when an error message came up telling me to check coolant level.....Now i jus recently put in some coolant although it is not the required coolant....But for some reason after my car started to overheat again, i open the engine coolant cap and there is hardly any coolant in there....I don't see any leaks comming out of the car so i am confused....Also before that error message "check coolant level" came on I had another error message saying "low-refrig a/c off".....Please desperately looking for some positive feedback....Thank You very much......

Answer
Jerry,
The low refrigerant message is the least of your worries right now. A partial charge should handle that without a whole lot of problems. I'd suggest getting it leak-checked also but depending on how low it is, and how often you need to partial charge the system, sometimes people would rather just top it off once in a while rather than go to the expense of finding/fixing the leak.
As for the disappearing coolant, sorry to be the bearer of bad news but coolant does not evaporate, so that only leaves leakage and ingestion by the engine as ways for it to disappear. If you're absolutely sure, there's no leaks, then I must tell you that it's very likely you have a leaking head gasket. This is a VERY common problem with the Northstar engine (the one in your car). You'll need to have it checked. I'd suggest that you get it done ASAP since every over-heat damages your engine more, and that increases the cost of repair.