Technical note

F5 cylinder-head coolant micro-leak — why compression ratio drifts

Technical note · not a test report for a specific unit

Slow coolant drop, occasional white exhaust, and continual handwheel advances to hold the same ignition delay suggest water around the head. Sealing faces, gaskets and cracks must be judged separately.

Do not force a hot strip

Reassemble, run-in, then rate. Minor seepage and a cracked head are not the same schedule. Related: cetane repair.

Next step

Tell us the engine model, the symptom, and the last rating run

A nameplate photo helps: research method, motor method, or cetane, and where the reading drifts.