Engine Performance:
Benchmarking Through
Spark Plug Analysis

By A.R. Brenholts Jr.

From the spark plug manufacturers' perspective, the routine and conscientious examination of spark plugs removed from service can make a meaningful contribution to the diagnostic regimens used to benchmark engine performance.		Virtually all spark plugs subjected to firing-end, deposit analysis have lube-oil derived elements in the deposit. In many instances, where the lube oil from the subject engines was being regularly analyzed, we have frequently found elements in the firing-end deposits that did not show up in the lube oil analysis. We conclude that power cylinder component wear can be occurring excessively and that conventional lube oil analysis can miss it. The wearing material in the power cylinder above the BDC position of the bottom-most piston ring may be vaporized, the bulk of it leaving the engine in the exhaust gases. If the thermally colder spark plug should get in the way of this vaporized material, it should cause this material to condense out on the plug's firing-end, thus capturing a clue to operating conditions within the power cylinder. The examination of the operating record retained by the firing-ends of spark plugs during their service interval should be regarded as one of the most revealing methods available for monitoring an engine's operation, establishing trend-lines of possible component wear events and rates. The following case studies illustrate the spark plug's ability to reveal wear trends of major engine components .
A spark plug is the recorder of a power cylinder's operation throughout the service life of the spark plug in a specific power cylinder. Since the spark plug is the most accessible power cylinder component, it can be the most relevant diagnostic aid available to the conscientious engine operator. Careful and informed inspection of the firing ends of all the spark plugs removed from an engine can detail conclusions regarding operating conditions. This information can assist in significantly reducing component failure, saving considerable amounts of downtime and money.