lkchris

Your $100K-plus car is VERY well engineered by Mercedes and there is virtually NOTHING you can do to improve it.

Spark plugs from K-mart aren't one of the things.

vettdvr

I have removed plugs for years and only with the long life plugs found s sieze problem. I use a breaker bar (about 30" craftsman I think). When I break the plug loose I don't try to remove it. I just move it about 1/8 turn. Then I tighten it. and repeat the process. Each time I move the plug a little more out. This has worked for me. WD40 would not seem to be much help as it won't penetrate down into the threads. There is also an issue with deposits building up at the tip that almost acts like a locktite. Just go cautious and they should come out. But don't try to break them loose and then just take the plug out. I do use neversieze on the new plugs. Jim

paulv

Well said. The only thing I've ever found at K-Mart or Wal-Mart that's appropriate for a MB is Mobil 1 0W-40!!! Actually, the Mobil 1 oil at Wal-Mart is "fresher" than what I've found at popular auto parts shops, now that I know how to break the date code on the bottles (thanks to a call to Exxon Mobil Cust Serv)

Regards,
paul...

mleskovar

I recently replaced my original plugs at almost 100K miles. All 12 gaps were still at recommended and virtually no wear was seen. They could have gone another 100K miles. No lead gas, exotic materials, and modern engine management systems have increased plug life considerably.

fritza2tt

mleskovar, you gave me the answer I was looking for: "They could have gone another 100K miles."
That's what we used to do with aircraft spark plugs over 50 years ago, take them out, clean them, gap them, test them and put them back into the engine.
Recently I went to my independent service station that specializes in Mercedes and asked them about changing the plugs for me. $300 for the labor alone! So I decided to forget it. The car has over a 100,000 miles on it and the original plugs still run perfectly.
The old saying: "if it ain't broke, don't fix it" never sounded better to me. With two plugs per cylinder, engine warning lights, checking fuel consumption etc. I'm sure that there will be plenty of warning when the plugs start to break down.
I'll continue to stick with the old set. :-)
Thanks for a good post.

paulv

Freidolin,

I hope that you can get the plugs out when the time comes and they haven't seized up in the cylinder head -- if that happens, spending $300 now would have seemed a bargain. Good luck.

Regards,
paul...

fritza2tt

Paul, I'm 77 years old and drive the E320 like a Diesel. Hardly ever get the RPM above 2,500. On the Interstate it is less than 3,000 RPM. In suburban driving I average 27mpg on the tank full, on trips it's closer to 30 mpg. As I said, "don't fix it, if it ain't broke!". Besides the plugs most likely will outlast me, and if not, I'll trade the whole thing in and let somebody else pull the heads to get the plugs out. :-)
And, I might yet be able to make some kind of a record for spark plug longevity - that is, if I live long enough. :-)))

mleskovar

Yea, just because they look like they'll go 200K doesn't mean I'd leave them in that long. They weren't easy to remove, the plug boots were hard to remove and replace as well. About an hour job once you've done it and figured out the right tools and procedures, but it took me 3 hours the first time. Don't clean exotic metal tipped plugs. Bosch says the metal coating they use on the plugs is anti seize and I believe it because they all came out OK...a little 'squealing' on a couple but no super effort or breaker bar required. The correct plug is expensive but with 100K recommended change interval it's worth it. I didn't notice any increase in power or gas mileage after the change so I believe the removed plugs were still working properly.

fritza2tt

mleskovar, thanks for your comments. But now you raised the issue with the plug boots and the wires. They harden and by removing them you probably do more damage than good.
Let's get back to spark plugs. The only thing that is supposed to wear are the points. You said there was very little noticeable wear when you pulled yours out. I would like to make a point here too, perhaps that's the reason MB sets the initial gap at .032". If the replacement plugs call for a .04 gap opening, (less of a chance for the spark plugs to foul,) that means that there is quite a spread that is useable. However, the wider the gap, the more prone are old ignition wires to break down!
(As a point of interest, I've been told that with magnetoes a narrower gab yields a hotter spark. Ever run across that?)
Other than at the points, there is no place for spark plugs to wear. The ceramic insulation may crack and break down from hard engine use and/or pinging. But pinging too has been practically eliminated with knock sensors. Leaves one last item, and I believe I mentioned it before, if one spark plug stops firing, pinging can result by the yet unburned fuel/air gases which should have been ignited earlier by the other spark plug. To me, this should be the primary reason for changing spark plugs at the recommended intervals. :-)

paulv

I honestly hope that you greatly out live the car. Best wishes to you, sir.

Regards,
paul...

mleskovar

I agree about the boots and wires....I was very careful with them and nothing broke. They weren't brittle by any means but I also didn't give them any sharp bends or pull on them. I haven't noticed plug tips wear since they started using platinum and lead was removed from the gas. I think the difference in gap is attributed to electrode design and composition. I noticed the replacement plugs had a diifferent/smaller electrode. My '54 English single cylinder motorcycle is magneto fired and the plug gap is .018" - .023". My understanding is that a wider gap increases the spark dwell but reduces the intensity (given the same voltage and plug). You may be correct that spark plugs are no longer wear items but I stick with the manufacturers recommendation of change at 100K. I know I'm in the minority but I believe the engineers that designed the cars know more about maintenance requirements than we do and there isn't any sinister secret attempt on their part to get more money out of us by reducing intervals or have the car wear out quicker by lengthening them.

ml350

I would like to know which bosch plugs for my ml350

Kestas

Bosch F 8 DPER.

ml350

is this type for my truck?

Kestas

Yes it is. Here's the link that shows it:
ML350 spark plug

nkpnkp

Guys oh and gals,forget all those technical detail. I have used both Platinum4 and regular plug just to see how car performs. Let me tell you, just use the normal plug specify in your book. Cost 1.25 as compare to 6.00 each. Besides cost diff. my 1995 E320 is just drive better. I wont mind paying six times more if it works but sorry it does not.

fritza2tt

Thanks Paul. More years have passed since we last talked on this forum. I'm now 82, still have the 1998 E320 but with 146,000 miles on it and still with original sparkplugs in the engine. My wife drives the car now. I drive an 1987 300D Turbo with 208,000 miles on it. Still runs like new and still looks pretty good too. Recently had to replace the lower balljoints and got talked into replacing the front shock absorbers with expensive Billsteins. Looks like both cars will outlast me without a problem. :-)))

lkchris

A couple years ago I looked at Bosch websites from various countries around the world and learned that the USA market is the only market in which Bosch sells "Platinum +4." (Or +2) The oil filters they market here at places like Autozone are USA-only items, too. As noted, K-Mart stuff.

The OE plug specification on any recent Mercedes is a platinum plug, too--just something much better than K-Mart stuff. They're more expensive for good reason.

USA auto parts superstore stuff simply doesn't translate to Mercedes and is instead mostly for guys fixing their Camaro in the Pep Boys parking lot by hitting the carburetor with a hammer.

grane

+2

fritza2tt

Grane, that was excellent advice. I'll do that too when the time comes. I now have 145,000 miles on the original plugs in our '98 E320 and am beginning to wonder what they will look like when they finally will have to come out. The original gap was, I believe, .029 ". They are bound to wear but should be able to go over .040" and still work normally. All depends how long the ignition wire insulation will hold up. The plugs you pulled out, how long were they in, what was the gap and how did they look? Sure would be interesting to know. :-)