You are seeing the begining of head gasket failure. The engine runs rough at idle because 2 adjacent cylinder are probably leaking acoss into each other which steals power form both cylinders to the point of acting like the spark plugs are misfiring.
The bubbles you are seeing are coming from 1 or more cylinders leaking through the head gasket. The leak is so small at this time that air is being pushed from the cylinder past the gasket into the water jacket because the cylinder compression is at least 100 to 140 pounds of pressure. This is much greater than the 12 to 16 pounds pressure created in the cooling system.
As the compression pressure tears at the gasket, the leak will get large enough for the coolant to pass back into the cylinder. This leak will start to occur when you shut the engine off and cylinder pressure drops to zero but the cooling system is still pressurized as the engine cools. This leak will allow the engine to overheat as the coolant will be displaced by hot cylinder gasses.
Now is the time to do some compression tests to determine which bank of the engine is affected although both head gaskets should be replaced while the engine is torn down that far. It will probably not do much good to use stop leak as the cylinder pressures tend to wear a "V" pattern in the gasket which makes it hard for stop leaks to form a good interlocking grip in the void and will push out easily. Be sure to have the heads checked for cracks and warpage while off the engine. This job runs $1500 to $2000 depending on the garage used.
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Wednesday, March 12th, 2008 AT 8:17 PM
