Recently, I removed the spark plugs from my brother's Ecotec for a visual inspection, and found that on two of them, the small platinum "dot" on the ground wire part of the plug was missing. Hopefully they made their way safely through the engine and out the exhaust. I haven't really had much experience using these type of plugs over the years, so I was just wondering if this is a fairly common failure, or just an unusual one in this case?
I was also wondering what experience people have with the change intervals on these plugs. GM says that they're supposed to be good for 160,000km (100,000 miles), but obviously in this particular case, that's not going to happen (they have about 75,000km on them). In my own car (2200 engine), I've currently got 119,000km on them, and they're working fine. According to GM I should be able to get another year out of them, but if I'm pulling them out for their annual inspection, I'm just wondering if I should have replacements on hand at the time. It passed it's emissions test around 101,000km with flying colors, and so far the gas mileage is staying stable, so I don't have any reason to believe that they're failing yet.
I'm just curious to see what others are using for their change intervals, and what problems may have been encountered.
Thanks,
John