What are wet and dry liners?

Wet and dry liners refer to different types of cylinder liners used in internal combustion engines to line cylinder bore where piston moves, providing wear resistant surface. Dry liner is cylinder liner that does not directly contact coolant, fitted into cylinder block with interference fit, with outer surface in contact with block material, not exposed to coolant, so it is dry, used in many automotive engines, can be replaced if worn. Wet liner is cylinder liner that is in direct contact with engine coolant on its outer surface, with coolant surrounding liner for cooling, sealed with O-rings at top and bottom to prevent coolant leakage, used in heavy duty diesel engines, marine engines, and some automotive engines, providing better cooling but requiring sealing. Wet liners are replaceable and allow larger coolant flow. So wet liner is cooled by direct coolant contact, dry liner is not, both provide wear surface for piston rings and can be replaced, with wet liners better cooling and dry liners simpler installation.