How many miles on spark plugs?? - Leaking compression spark plugs !!! Replaced them at 100K km, at first they seem to look fine, gap is OK (Clean and shinny good condition of iridium and platinum coating) - could easily done 200K km on them. Saving them as spare parts... BUT ATTENTION : Although the gap is OK, 2 of the plugs exhibit compression loss (leaking plugs) - just starting to leak. This seems to be caused by over torquing or too much hours of use (my case probably). Can lead to a bad ignition coil. So inspect them each interval by the book.(can use a hole camera without taking them out to only to check for leak, or take out for full inspection) - (here is an example of really bad leakage: - - https://www.google.co.il/imgres?img...9LPAhUEXRoKHQG7BRkQMwgeKAIwAg&iact=mrc&uact=8 , - - https://www.google.co.il/imgres?img...9LPAhUFfhoKHbkgBowQMwgkKAcwBw&iact=mrc&uact=8 )
By "Leaking" you are referring to electrical leakage of the spark due to corona discharge along the porcelain to the steel body? Dirt, grime, and wet or oily residue on the porcelain or rubber boot of the cap can provide a conductive path for electricity at High Voltage--that's why you want to keep your doodads clean and dry. This is an ideal place to be using that thick Dow silicone dielectric grease to lubricate the rubber boot and keep moisture off the porcelain.
Compression Loss (the ceramic/porcelain and steel hexagon + metal shell around it are "gapped" - don't hold the compression pressure within the cylinder ). Take a look here : http://www.agcoauto.com/content/images/engine/spark_plug_leaking_around_ceramic.jpg http://www.agcoauto.com/content/news/p2_articleid/208 Or here: http://www.agcoauto.com/content/images/engine/spark_plug_leaking_around_ceramic.jpg http://swiftautocareservice.blogspot.co.il/ : "COMPRESSION LEAKAGE: Spark plugs can leak compression around their bases appearing in yellowish colour. When this occurs, excessively hot compression-gas may destroy coil-on-plug type of ignition coils. Compression leakage at the ceramic base results from age and can result to engine pinging and detonation. Ping: A mild noise the engine. Detonation: An occurrence in the internal combustion of an engine, where the compress air-fuel mixture explodes violently instead of burning smoothly. Always have spark plugs inspected, when mileage approaches the recommended interval as guided by manufacturer’s specification. For instance if the recommended replacement interval is 100,000km, two or more plugs might be removed for inspection around 80,000km."....
