Water Jacket
Passages cast into the engine block and cylinder head that allow coolant to flow around the combustion chambers.
A water jacket is a network of hollow passages cast into the metal engine block and cylinder head that surrounds the engine's cylinders and combustion chambers. Engine coolant is pumped through this jacket to absorb the intense heat generated by combustion and friction.
The cooling system relies on the water jacket to transfer heat away from critical internal components to the coolant, which then carries it to the radiator to be dissipated. The shape and placement of the passages are carefully engineered to prevent hot spots that could cause localized metal warping, pre-ignition, or head gasket failure. The cylinder head gasket features matching holes allowing coolant to flow from the block up into the head.
Over time, using water instead of proper coolant or failing to flush the cooling system allows rust, scale, and mineral deposits to build up inside the water jacket. This build-up acts as an insulator, blocking heat transfer and causing the engine to overheat. In severe cases, corrosion can eat through the cylinder wall or engine block casing, leading to internal coolant leaks and engine failure.