One of the many valuable tasks a leak-down tester will allow one to perform and or determine is the condition of the bore in various locations revealing damaged areas that are not evident from wet or dry compression stroke tests/comaprisons. Conversely these tasks are accurate even with a “cold” engine. Remember with a leak-down tester we introduce outside pressurized air verses requiring the engine to mimic a pump with all its inherent shortcomings. The bore condition is revealed by introducing a regualted and maintained air resource; lets say 100psi while noting the percentage of losses. subsequently we slowly rotate the engine through its stroke, notable increases in losses indicates damage in the specific area (perhaps the bore is galled, Nikasil or chrome plating is damaged or there is an imperfection in the bore i.e., pits-gouges, maybe out of round or who knows what?

Other problematic areas become obvious too, such as gaskets, oil seals and crankcase leaks. None of the above for the most part is notable with a compression tester.