OK guys, I had the wife'* 03 Bonneville SSEi (75K) on the lift Saturday to change the oil (Mobil 1 out and Mobil 1 in). It looked fine no foam/chocolate milk. After getting it down on the floor I was adding the oil back in and checking the other fluids. I noticed the coolant tank was nearly empty...I topped it off with about 1/2 gallon of Prestone (universal type) antifreeze. After driving the car and pulling into the garage I actually had a "whiff" of antifreeze, the first time this has happened. I have checked the floor for leaks but have found none. I have suspected the water pump is going bad as it "whines" a bit at start up. But I have no coolant leaking form the area...that I can see.

I suppose that I should have a pressure test done to see if the WP is leaking under pressure. But I also know that the UIM and the LIM are prone to problems.

Any suggestions for me? If it is the UIM or LIM gaskets is there a write up on the procedure of R&R? Thanks for your help.

I'd pressure test it. The supercharged cars aren't prone to UIM failures because the UIM is a metal supercharger whereas the non-charged motors are a plastic UIM. The LIM gaskets on our motors typically look horrible when we change them, yet they aren't a normal source of coolant loss. A couple years back there were a few show people here that liked to run around ranting and carrying on a great show. In the end, it'* was just a show. 99.99% of bad LIM gaskets look bad and don't create any issues, don't put coolant in the oil and don't cause a breakdown.

Being that you smell coolant, the chances of it being an internal leak are extremely low unless you are sniffing the tail pipe. I would start by looking around the engine bay at the throttle body, thermostat hosing, hose connections, radiator end caps, coolant elbows, water pump and heater hose fittings. All these areas contain coolant with a seal or something that can leak.

OK pressured it up and it leaked down from 15# to 10 # in about and hour. But no sign of fluid anywhere. Then I brought it home and I could see a little fluid on the ground and could smell it again. It appears to be coming from the passenger side up near the radiator. Are the radiator in these cars known for having problems? I know that some GM vehicles are known for the side tanks de-laminating.

I'm taking it back to school tomorrow and put it up on the lift to see we can see anything from the bottom.

Check the lower radiator hose. Get the system up to pressure and look for any seeping. Repair or replace what is needed.

Known isn't quite the word I'd use. Plastic end cap tanks in general do have problems sometimes. The heating and cooling cycles can crack the plastic tank where you can't see it and only weep when up to temp etc.

Makes for an annoying item to find.

We did this in my mom'* Taurus one time.

UV Dye

+

Black light

=

Leak lit up like a Christmas tree

going to get it up on the lift and try to figure out where the problem lies. Just glad that I finally saw some seeping. I'll keep you posted. Thanks!