Great news. Cannot argue with success. Keep an eye on the coolant level in the reservoir. If it starts going down, you can add a bottle of dye to the coolant, drive the car until the level goes down some more, then search with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If you find it inside the tail pipe, suspect a leaking head gasket.
Your mechanic can also perform a "sniffer" test. That involves drawing air from the radiator through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are present, that liquid will turn bright yellow. Combustion gases get forced through a leaking head gasket, or less commonly through a crack in the head, and cause that air pocket by the thermostat, and when the engine is off and cools down, coolant is drawn into that cylinder and forced out the tail pipe later. Coolant can also be sucked into the cylinder while the engine is running.
Monday, December 26th, 2011 AT 10:45 PM