Leak Down Tester

The Longacre Leak Down Tester (SKU LON52-73010) is an essential diagnostic tool for engine builders, performance mechanics, and serious automotive enthusiasts who need to assess cylinder seal integrity without complete engine teardown. This precision instrument detects compression leakage through worn rings, valve seats, head gaskets, and piston damage—critical information for tuning decisions, rebuild validation, and performance troubleshooting. Whether you're diagnosing a tired engine or verifying machine work before reassembly, the leak down tester reveals compression loss percentages that compression tests alone cannot identify, making it indispensable for anyone committed to understanding their engine's true condition.

The leak down test operates by introducing regulated shop air into each cylinder at top dead center, then measuring the percentage of air that escapes past sealing surfaces. Unlike a compression gauge that only shows overall pressure, this tester isolates leakage to specific failure modes: escaping exhaust indicates worn rings or piston damage, leakage into the cooling system signals head gasket failure, and air exiting the intake manifold points to faulty intake valves. The Longacre design delivers precise, repeatable measurements across all engine types and displacements. Its compact 8.4 x 4.6 x 10.3 inch footprint and 2.5 lb weight make it equally at home in a race shop, dyno facility, or mobile service setup, while the robust gauge fittings withstand the demands of frequent professional use.

Mechanics and engine builders rely on leak down testing when compression readings suggest issues but don't pinpoint the cause, when validating machine shop cylinder work, or when tuning engines for maximum reliability and horsepower. The procedure works on any four-cycle engine—gasoline, diesel, or forced induction—from small-displacement single-cylinders to large-displacement V-8 platforms. Setup requires only shop air at 90–100 PSI, spark plug or glow plug holes for cylinder access, and basic hand tools to rotate the engine to TDC per cylinder. This straightforward methodology makes the Longacre leak down tester the go-to choice for diagnostic shops, performance builders, and technicians who demand data-driven decisions.