gm leaking coolant
 

Aloha. While the 19 year old mercedes is running great, the wife took HER 6 month old GM car to the dealer due to it losing coolant.

This car has the 3.4 liter engine that is known to have intake gasket problems.

The dealer said they pressure tested cooling system with no leaks found. they say overflow tank shows signs that coolant came out of cap and ran down due to being overfilled. We never filled it! There was also something burned on the top of the reservoir bottle. It was black and I doccumented this with photos.

Is there any reason the reservoir would be losing coolant? If not then why is the dealer saying there is no problem?

I apologize this is not Mercedes related, but I don't know where else to turn.

I've joined an online petition to try and get GM to recall this issue.

Any help is greatly appreciated.

Yes it does sound like a blown head gasket. It passes the pressurizing test, but leaks when combustion pressures act on it. Leak path is combustion gases into the coolant, causing an overpressure condition. When you get around to it, try looking in the radiator when the car is idling and look for bubbling or foaming which would indicate a blown gasket. Better yet, radiator shops have a way of detecting combustion gases in the coolant. Sinc your problem appears subtle, you may want to pay them a visit.