Lisle Combustion Leak Detector

Lisle's 75500 combustion leak detector gives you a fast, visual way to check whether combustion gases are leaking into the cooling system. Bad head gaskets, cracked blocks, and warped or cracked heads all let exhaust gases push into the coolant, and this tool catches that before you start pulling the engine apart.

How it works is straightforward. Fill the detector chamber with the included blue indicating fluid, place the tapered end into the radiator neck with the engine running, and draw vapors from the cooling system through the fluid using a vehicle vacuum line or hand vacuum pump. If combustion gases are present, the fluid changes from blue to yellow. No gases, it stays blue. The color change is clear and unmistakable, which removes the guesswork from diagnosing overheating problems, coolant loss, or white exhaust smoke.

The tool comes with the detector body, indicating fluid, and replacement fluid for additional tests. At about a pound of total weight, it is a compact diagnostic tool that earns its keep quickly. Catching a head gasket leak early can save a customer from a much more expensive repair down the road.