Green or brownish coolant leaking from hoses or other engine components onto the ground can be the first sign of a head gasket leak. However, when coolant is leaking internally, it can be harder to determine and may mean there is a blown head gasket. If your vehicle is exhibiting other symptoms, such as overheating and decreased coolant levels, there is a radiator cap test, or what is commonly referred to as a champagne test, you can perform. The champagne test can determine if the head gasket is leaking or blown.
Turn the car's engine off and allow it to cool overnight. Open the hood and prop it up with the hood support rod in the engine bay.
Locate the radiator cap toward the front of the engine bay. There is typically a warning message imprinted on it such as, "Do not open when hot." Turn the cap counterclockwise to open it and set it aside.
Start the vehicle once the cap is off. You will see bubbles in the coolant, when you peer into the radiator filler neck, if the vehicle has a leaky or blown head gasket. If the test is positive for a leaky head gasket, you should take the vehicle in to be worked on by a qualified mechanic.
