Some instances of emulsified oil appearing on oil filter caps have been reported by dealerships during new vehicle preparation. The emulsified oil has been determined to be caused by humidity in the rocker arm cover accumulated during shipment from Japan and is not the result of an engine coolant leak. This is a recognized condition in imported vehicles at port of entry. The emulsion disappears after initial mileage except in cold damp climates where air passing over the oil filler cap, due to its location in the vehicle, may cause condensation on the inside of the cap forming as emulsion.
In the event a customer is experiencing engine coolant loss, the routine diagnostic procedure should include a cooling system pressure test, a check for coolant in engine oil pan, and a check for evidence of an external coolant leak at the head gasket before installing a new head gasket. The head gasket should not be changed when emulsified oil on the oil fill cap, PCV valve, and/or oil fill neck is the only symptom.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.