Date registered: Aug 2008
Vehicle: 2008 E320 Bluetec, 1988 560SL totalled unto death). 1997 Dodge Ram 1500, 1983 300CD
Location: Greater Metropolitan Beaverdam, Virginia
Mentioned: 3 Post(s)
Quoted: 152 Post(s)
Remove the plugs and look at them. If unconclusive, replace them. It is an inexpensive preventive maintenance.
Modern engines, including those in MB (you don't say what engine and year you have) like to sell the "100k mile spark plug life" feature. Even if true it is my opinion that leaving spark plugs in place for 100k miles, which can be 10 years for many, is looking for trouble. Most engines these days have aluminum heads. Having a spark plug remain installed for a long time invites a very expensive repair to remove/replace them when corroded in place. I suggest removing the plugs every year or two to inspect them, giving an idea of the combustion quality, clean and gap if needed, and replace with a thin coat of anti-seize on the threads.