No experienced engine builder would intentionally bolt a cylinder head to an engine block without installing a gasket between the block and cylinder head. The gasket seals the block deck surface to the cylinder head surface. Smooth-looking metal has microscopic surface roughness and waviness that creates leak paths, especially under high cylinder pressures. The gasket fills the voids and contains those high pressures. That’s why high-horsepower engines O-ring the blocks and heads. Those same microscopic peaks and valleys exist on the cylinder walls, piston rings, and piston-ring grooves. Motor oil acts like a gasket to seal those components together.
tested an engine—hot or cold—you’ve probably seen a difference in the readings. Part of that is due to the thermal expansion of the
