In all fairness "NOW" MB wants the (platinum tipped) sparkplugs changed at 100,000 or 4 years(4 years I believe pertains to what Albert is saying about being careful not to strip the threads!), but they are expensive plugs. MOST manufacturers have the same plan it seems like.
At one point pre-FSS engines were at 15,000 INSPECT and replace IF NECCESARY, and at 30,000 REPLACE (I don't know the implications of replacing them if they need it at 15,000, then what do you do at 30,000, automatically replace them if they only have 15,000 miles on them?).
There were some interim replacement mileages between "non-FSS" and "strictly FSS" (around 98 or so up to 1999 on the M111 and M104 motors, sorta like "non-FSS" engines living in an "FSS" world) where the were calling for 45000 and 60000, depends on the individual chassis).

One thing that bothers me about service intervals in general and spark plugs in particular is that there is nothing taken into account for the amount of HOURS the engine is operated. The engine is still running when sitting in a traffic jam, and the plugs are still sparking, although not as many RPM's.
Gilly

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Mr Champion,

Here is a question I have posed before but no one touched it. On my C230 4-banger, Each of 2 coils drives 2 spark plugs, at opposite polarities. This is similar (as far as I know) to the old Citroen that had 2 cylinders and one coil. This should cause the inner electrode to wear on one plug and the outer electrode to wear on the other plug (I think). I recall hearing that on the old Citroen it was recommended to "rotate" the plugs for even wear. Does any of this apply to the Mercedes engine and does this have anything to do with the statement that these engines "hate platinum plugs" Also, I have been told that the recommended factory plug is not platinum.

Thanks,

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

i don't examine too many spark plugs from gasoline-fueled, light duty engines. but i do see spark plugs from negative-ground and positive-ground ignition systems using a coil per spark plug. most of the electrode erosion is always on the center electrode. and there is a reason: it operates at higher temperatures than the ground electrode...more of the center electrode material is vaporized with the arc because of its higher sustained temperatures.

in my experience, platinum electrode spark plugs are a marketing gimmick.