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Old 07-07-2005, 06:02 PM
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Join Date: May 2003
Location: bullhead city, az hot as hell
Posts: 301
spark plugs for 300e

I thought I remembered a post on plugs and it said not to use plat. only the supers,I had to use bosch plat. yesterday as I had a couple of fouled plugs and that was all I could find, I have some bad valve guides and haven't had time to put the new head on, I drove them 300 miles home and they were cleaner than the supers, should I keep running them?

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Old 07-07-2005, 06:27 PM
Join Date: May 2005
Location: san francisco
Posts: 27
interesting (plat plugs)

I was told the same thing...don't use platinum...

I'm not 100% sure why though....also would love an education!


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Old 07-07-2005, 07:16 PM
Posts: n/a
In the case of a 103 engine in good condition, the standard Bosch copper plug will run better and give a better idle. The reason is that the center electrode of a copper plug is much larger than same on a platinum plug. This is because the platinum is such an expensive material. The wider electrode makes a fatter spark, thus the improvement.

In the case of an oil fouling engine, the platinum will be more resistant to the oil fouling. After you replace the valve seals, go back to the copper.

Good luck,
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Old 07-07-2005, 07:21 PM
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Join Date: May 2003
Location: bullhead city, az hot as hell
Posts: 301
thanks larry, after I put the replacement head on I will go back but untill then I will enjoy not having to clean them as often
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Old 07-07-2005, 07:34 PM
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One other point. Due to the brittleness of platinum, platinum electrodes have been known to break off and ruin engines. This is not a common occurrence, but I thought that you should be aware of the risk.

Good luck,
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Old 07-07-2005, 08:57 PM
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Join Date: Apr 2001
Location: Joliet Illinois
Posts: 309
I agree with Larry

I have had good performance from the standard Bosch Plugs and NGK TR5 (resistor plugs). I think earlier model M103's used a non-resistor plug and later ones use a resistor plug.

I tried Bosch platinums in my Volvo once and it started idling rough after a short time. I replaced the platinums with standard plugs and it was fine again. Ever since then I have shunned platinum plugs.
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Old 07-07-2005, 11:44 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,144
The other issue is that the OE Bosch plugs are NON-RESISITOR, and the only readily available (from Mercedes parts specialists) non-resistor types are Bosch. You will likely NOT find non-resistor Bosch plugs at McParts. I've brought this issue up several times including a couple of days ago.

The resistors alter the secondary voltage wave form, which is what can cause poor idle or busted emission tests.

Go to the Fastlane link and buy Bosch H9DC or H9DC0. The later is OE and has a "heavy duty" electrode, but is more expensive, and the H9DCs work just fine for their 30K normal service interval.


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