A head gasket (48) which acts, when clamped between a cylinder head (28) and a block (22) in a liquid cooled internal combustion engine (20), to form a seal around the combustion chambers (24). A coolant flow path (32) routes through the engine (20) and its directed, in part, through the cylinder head (28) and the block (22), with a corresponding flow opening (54) formed in the head gasket (48) to accommodate flow of liquid coolant in a normal direction. The head gasket (48) includes a one-way valve (58) positioned in the flow opening (54) to allow the flow of coolant in a normal direction but to prevent the flow of liquid coolant through the flow opening (54) in an abnormal, reverse direction. The one-way valve (58) includes movable gate (66) which may be biased against a valve seat (64) in a normally closed condition. The one-way valve (58) can be made as a loose piece article of manufacture which is held in flow opening (54) by self-locking retention clips.