Hello, I was going to check and change the spark plugs on my car due to some rough idle problems that previous posts have also mentioned. The car has approx. 110k MB serviced and was wondering when they are usually changed or at what mileage are they changed according to regular service (should wires etc. also be changed)? What is the exact oem spark plugs I should purchase and what is the gap spec.? This is a very novice question but do they not come at the correct gap spec and how should one go about adjusting them? Finally could someone tell me what I should torque them to?

Thank you

If you are going to be servicing the car yourself, you should get the CD from us if you don't have one. You need the 124 CD's. The spark plugs should be the Bosch copper core, Not the plats. The gap is .8-.9mm. I don't remember the specific torque.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Hi Benzmac,
Why the copper vs. platinum core? I figured the platinum would be a natural evolution, technically, but simply wasn't around when the M103 was developed.
Thanks, as always

I think you may have answered your own question. The m103 (or m102) engine was not developed with the plats in mind so they and a lot of other non-computer controlled variable valve timing engines have difficulty dealing with the kind of spark they produce. One of the most common problems I have seen is a sudden drop in power (especially under acceleration) with the use of the plats. Stick with the coppers.

yal
88 230e (W124)

Thanks for your input, yal. I guess I'd like a technical (engineering/ physical chemistry) analysis of why the spark and the engine's response might be different between them. I've been running the platinum plugs in both my MBs for about 120,000kms worth (combined) without ill effects, but results from such a small sample size are just anecdotal.
Engineers, techs?

Hi Nick,
I've been steering people away from the "mass-market" (tiny electrode) platinums since I tried them 10 years ago.I have no problems with the real Platinum plugs ($18.00+ each)that Bosch has made for Porsches for eons(other than the cost/benefit). The problem with the cheap Platinum plugs is the small size of the center electrode and the fact that since it doesn't have enough rigidity to support itself,it can't protrude beyond the end of the insulator. In cars that run a relatively rich fuel mixture the plugs tend to arc down the center insulator to the shell. In a test chamber (an old Champion Spark Plug cleaner/tester)using compressed air to simulate conditions in the engine,the difference between the Platinum plugs and standard Copper-Core is obvious. The Platinum plugs produce a very thin thread of spark compared to the copper-core plugs. The spark plug's mission is to initiate combustion. A "fat" spark hits more molecules of the hydrocarbon/air mixture than a thin spark.The more molecules that are "hit" with the spark,the more efficient the combustion process. Try going back to the standard plugs gapped to 1.0 mm (.040")and see if the idle and acceleration "feel" better. The consensus among Techs (from empirical data)is that copper works best in a Mercedes.
Regards,
Randy D.


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W.R.Durrance
ASE Master Tech
Mercedes Tech 20 Years
68 250SE
68 SAAB 96 Ice Racer
69 300SEL 6.3
70 300SEL 3.5
81 300TDT

Wow...that's an answer!

Sometimes I am totally amazed by the depth of talent available on MercedesShop.

GREAT ANSWER Randy D. to a question that many people have had. I tried platinum plugs on my '91 300E and didn't notice any improvement...maybe some degradation. I always wondered why.

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Bill Wood - Webmaster
MercedesShop.com, LLC

Folks,

I believe platinum is used to prolong the time between plug changes. Platinum is very superior to copper in terms of corrosion and erosion in the combustion chamber environment. However I believe copper plugs use a large diameter copper electrode to carry power (copper is dirt cheap.) Platinum (expensive metal) plugs use much smaller diameter tips and are not able to carry as much power. Dose the power (length of spark is function of voltage) make that much difference in your car? I do not know.

Reza

For what it's worth WRT this subject, it was pointed out to me by a master mechanic long ago that plats more often than not can not match the correct heat range of the OEM copper core plug that the engine was originally designed to use. Just another nuance to consider. So if your engine was originally designed to use plats, by all means do so. Otherwise, I would steer clear of them.

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Fred Prickett
85 500 SEL, 241,500 mi
90 5.0 Mustang LX conv.

KenT,

Thanks for posting the question. There aren't too many days that go by when there's not something new to learn on this forum. I join the webmaster in thanking WDurrance for the answer.

My dad had an independent garage in the 50's and 60's and that was the last time I remember evern thinking about one of those old spark plug testers. Some old ideas are timeless.

It's easy to see that WDurrance is a natural born tester/experimenter.

Thanks for the good info.


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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in
Mercedes automobiles

Thanks for the responses, especially WDurrance! It's always wonderful having an explanation that speaks from both technical theory and practical experience. Sometimes I marvel at the collective effort that 'strangers' make on this site!
Regards to all,
Nick