How to know if your head gasket is blown

A leaking, or “blown” head gasket will come with some pretty obvious symptoms. That is because what is happening in your engine is that two parts of the engine containing two different fluids – that are normally kept separated by the gasket – now have a path between them for fluids from one part to spill over into the other.

The head gasket sits between the block, where the cylinders and pistons are; and the head, where the intake and exhaust manifolds, spark plugs, and valves are. Oil circulates around the head, lubricating everything. Coolant circulates in a space around the cylinders called the “coolant jacket”, which helps the engine maintain a steady operating temperature.

When the gasket develops a leak, oil vapor can be forced into the coolant stream (along with combustion and exhaust gasses from the cylinders), and coolant will find it’s way into the oil sump and valve cover atop the head. Coolant may also find it’s way into the exhaust, and you may notice a rapid loss of coolant when this happens.

The injection of hot oil vapor and really hot combustion gasses into the coolant will lead to an overheating problem. You may notice a fair and steady loss of coolant as well. Since coolant is water-based, oil traces will float on top of the coolant in the radiator, and in the coolant tank next to the radiator. Coolant in the oil will deposit in the oil sump and inside the valve cover atop the head as a greasy brown “chocolate milkshake gunk”.

Like this:

Oil in the coolant can (sometimes) leave a “mayonaise” residue on the radiator cap. Same idea, only whitish instead of brown.