well, thnx, gerrry. it's been a while. all is well with you i trust. i see you finally splurged for the 500e. was it the one you once told me that you had your eye on?

concerning spark plug change intervals...

i think that there is no simple answer. how you are using the engine might govern change interval considerations. for instance, if you are using the engine in a continually high peformance, racing mode, i would be replacing spark plugs with some frequency[i.e., before each event].

on the other hand, if you are using the engine as a daily driver in urban traffic, with few italian tune-up opportunities, you could empirically determine the change interval on your own. to do that, i would install a fresh set of plugs after having checked them electrically and checked the gap dimension. i would make sure to fit them using an accurate torque wrench. and i would keep a log. recording all gasoline purchases and figuring out your miles per gallon at each fueling. at 5,000 miles, pull the plugs and examine them with a magnifying glass, measure the gap dimensions. repeat this inspection every 5,000 miles. at some multiple of these inspection intervals, you will conclude at what mileage level the spark plug's require replacement.

if you have access to a scope and can determine secondary voltage levels for each cylinder, this would be important evidence in the determination of when spark plugs should be replaced. however, for this to be a relevant measurement you would want the engine to be "loaded" - idling would not be a particularly relevant condition.

there may be another consideration governing spark plug change intervals, however. and it is a consideration that i don't know how to weight, since i have little experience with aluminum cylinder heads. i have heard that there may be an argument favoring spark plug change-outs so as to prevent the galvanic welding of steel spark plug shells into aluminum cylinder heads. it's possible i suppose, but so far i have seen no proof of it occurring with an engine that is operated from time to time.

in my experience, most spark plugs that are difficult to remove have either been cross-threaded or over-torqued. and that is why i recommend a balance beam torque wrench for plug removal. note the beam deflection. for most 14mm spark plugs, if the beam deflects to an indication of 65 ft lbs and the spark plug remains unmoved, it is a warning to stop and think about how you want to proceed - because continuing to force the issue will probably cause you to break off a spark plug at its thread relief.

i am always astonished at how many will force the issue, doing damage, rather than reaching for the penetrating oil and practising patience.

never try to remove a spark plug from a hot engine if you can avoid doing so. let everything cool down.

lastly, the removal of tetraethyl lead from fuel radically altered spark plug life. the absence of lead salt deposits can allow spark plugs to last for thousands of miles beyond the experiences of the leaded fuel days.

there are other issues that govern spark plug durability, however. 2-stroke cycle marine engines do things to spark plugs that are not done by automotive application 4-strokes.

i have addressed the issue with you assuming your interest is spark plug change intervals for daimler-chrysler vehicular engines.

happy trails...