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  #1  
Old 03-15-2003, 06:44 PM
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Some versions of Bosch Platinum plugs O.K. for Mercedes engines

In the Technical & Restoration Forum in the March / April 2003 The Star Magazine, there is a question about platinum plugs and an interesting reply. It doesn't say who exactly wrote the reply, but it was probably Stu Ritter:

After I put Bosch Platinum +4 spark plugs in my 190E 2.6, a dealership advisor reprimanded me, saying they aren't recommended by Mercedes-Benz. He said that a service bulletin indicated that they should not be used. Is this so?

Some time ago a Mercedes-Benz service bulletin recommended against using fine single-wire platinum electrode spark plugs in their engines. The electrode on these plugs was so thin that the spark could be blown off the plug, causing misfires. The new Bosch +4 spark plugs are not covered by that old bulletin. Thin-wire plugs could cause poor idle quality and misfires at high rpm under full throttle. Mercedes-Benz has not recommended against the newer +4 plugs, which have four electrodes so are not about to have the spark blown off. You might tell your service advisor that serval versions of Bosch platinum plugs exist.
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Last edited by suginami; 03-15-2003 at 10:39 PM.
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  #2  
Old 03-15-2003, 10:28 PM
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Wonder if these +4 plats by design have more resistance and if so, what is the net affect of this on the ignition system?
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  #3  
Old 03-15-2003, 10:38 PM
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suginami

i was just coming to ask about a bosch plug.

i went to advance auto for plugs asking for W9DC the person said bosch replaced them with WR8DP. they are different they have the ceramic cone all the way up the center electrode. the electrode is very small in diameter.

now after reading the above i'm guessing this is a thin wire plug. are these ok to use in the 4.2 420sel???

if they are ok what would the proper gap be. it actually looks like it is already set because if you would try to open up the gap the point arm will be pulled away from the center cone.

help should i use these or should i go back and try for a different type?

tks much
craig
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  #4  
Old 03-15-2003, 10:58 PM
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This sites Fast Lane and a few other MB WEB providers show W9DCO as the std. plug. W9DCO and W9DC are the same plug except the W9DCO has a slightly wider electrode - might fire a tad bit better.

I use Auto Zone for tool rental..ie...cooling system pressure tester, etc. Beyond that - zip.

I wouldn't believe squat an Auto Zone parts person had to say about an MB or any other Euro make. Everytime I've ever been inside one, there was always someone at the counter returning a part that "didn't fit".

Buy your MB parts from someone who knows your car.
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  #5  
Old 03-15-2003, 11:09 PM
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Oh the dilemma.
I have successfully used Bosch Platinum + 4 plugs in some applications, but have not tried them on my Mercedes.
For my car ( 2000 C230 K ), Bosch lists a +4 plug, but I decided to stay with the F7 KTCR, as called for in the manual.
You can not adjust the gap of an +4 plug ( says so right on the box ).
Even though the +4's have 4 ground electrodes, they still have just one fine wire centre electrode.
To each his own, I guess.
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  #6  
Old 03-15-2003, 11:26 PM
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on the bosch w8's or w9's what is the proper gap?
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Craig

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
See My Cars at:http://mysite.verizon.net/res0aytj/index.html

Pound it to fit then Paint it to match!

There is only First Place and Varying degrees of last!

Old age and deceit will overcome Youth and Enthusiasm every time!

Putting the square peg in the round hole is not hard... IF you do it fast enough!

Old enough to know better but stupid enough to do it anyway!
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  #7  
Old 03-15-2003, 11:55 PM
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Just went thru the MB maint manual - 1981-1993 - no gapping info for plugs?? I must have obtained mine from the Haynes manual or the Ritter-Easley site back when I bought it.

The factory calls for what amts. to .032 for M103 plugs - not sure about an M116 engine. Perhaps one of the many 420 owners will provide that info soon.

The search facility should locate it for you.
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  #8  
Old 03-16-2003, 01:32 PM
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Just my $0.02 worth. I just tried the plat w9dp plugs in my 84 500SEL and it was a big mistake. Ran terrible. With no other changes, put in NGK BP5ES (?) plugs and the car runs great again.
I don't know about the +4 but I don't think I will try them. The w9dc or w9dco or the NGK work so why take a chance again.

Paul
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  #9  
Old 03-16-2003, 01:43 PM
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All Bosch Platinums are resistor plugs, and the Bosch supers are NOT. MB stock wires have resistor plug connectors, so if you want to use platinum plugs you must either replace the wires with non-resistor wire (using the stock ends) OR replace the stock ends with non-resistor ends, using the stock resistor wire.

Under those conditions, they work very well. I put +4s in the 300TE on the advice of my MB mechanic, who only uses platinum plugs. No issues except rough idle, and that is dead engine mounts more than anything else.

Peter
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  #10  
Old 03-16-2003, 02:11 PM
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Quote:
Originally posted by psfred
All Bosch Platinums are resistor plugs, and the Bosch supers are NOT.

Peter
Gee, I hate to be anal about this.
My Bosch F7 KTRC ( Super ) plugs, are resistor plugs.
The " R " in any sparkplug stands for resistor. Just for the hell of it, I measured the resistance, and it is @ 1500 ohms.
Btw., the "T" stands for triple electrodes and the "C" is for copper.
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  #11  
Old 03-16-2003, 04:58 PM
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Stock plugs (those initially installed and recommended/listed) for replacement are not resistor plugs, the resistance required for radio noise suppression and coil life is in the wires and boots.

Bosch makes all kinds of plugs...... just make sure you don't have too much resistance in teh secondary circuit or you will have idle problems and high rpm/high load misfire because the spark won't make it across the gap.

The advantage of platinum electrodes, thin film, thin wire, or the large wire/side electrode ones is that the platinum ionizes the air much better, so the spark forms better. It also does not plate off (evaporate), so there is no electrode erosion. Size of electrode is more or less irelevant, the spark size and temperature is determined by the ionization path and wattage. A hotter, "smaller" spark will ignite the air fuel mixture better than a fat, cold spark every time.

Peter
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  #12  
Old 03-16-2003, 05:14 PM
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[QUOTE]Originally posted by manny
[
My Bosch F7 KTRC ( Super ) plugs, are resistor plugs.

This is what my manual calls for.
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  #13  
Old 04-22-2003, 01:46 PM
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I'm getting ready to change the plugs on our C36 engine which use Bosch copper-core F8DC4's at just slightly under $2 each wholesale.

If I remember correctly, one issue of "THE STAR" stated that the newer 4-electrode Bosch platinum plugs (pn#4418 for the M104 engine) really are better and can be substituted for the Bosch copper-cores. Of course, this is a 200%+ premium over the F8DC4's.

Did I remember, read, or interpret this wrong?

BOSCH is backing this up with a 100% part refund that states:

"you will feel the improved performance in your vehicle when you use Bosch Platinum+4 spark plugs. If you do not experience smoother acceleration, improved fuel efficiency and optimal engine performance, return the plugs with your dated sales receipt and Bosch will refund the purchase price of the spark plugs."

The coupon can be found here:
http://www.boschusa.com/AutoParts/SparkPlugs/PlatinumPlus4/

TIA,

:-) neil
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1993 500E
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  #14  
Old 04-22-2003, 02:02 PM
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Multiple ground electrode spark plugs are a gimmick! A smaller electrode mass is usually an advantage because all that electode mass can tend to quench and incipient flame kernel. The ground electrodes are quite "cold" relative to the 4500 degree F temperature of the incipient flame.

The resistor issue was also brought up. Using a resistor plug in place of the OEM non-resistor plugs can alter the voltage wave form and cause idle/emission problems.

Few manufacturers offer non-resistor plugs, so it's best to use the proper Bosch non-resistor plug. Some chains that sell Bosch plugs do not stock the entire line and will try to sell you a different Bosch number. If they don't have the OEM equivalent plug, shop elsewhere. Buy the OEM plug or be sure you have the EXACT equivalent plug from another manufacturer.

The only thing I'm not picky about is the "0" suffix, which indicates a slightly larger electrode. For example the OEM Bosch plugs in my 2.6 are H9DC0, but I currently use the H9DC.

In theory the H9DC0 might have longer electrode life.

Duke
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  #15  
Old 04-22-2003, 02:46 PM
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IMO, the best plug to use is NGK copper.


A common myth about platinum plugs is that they don't foul....this is simply untrue. In fact they foul more easily. On my 911 I switched from OEM NGKs to Bosch Platinums...I saw zero benefit and an increased fouling rate.

I agree that the multi-electrode, non-electrode, splitfire designs are gimmicks.

If you really want to maximize the potential of you plugs then "index" them. But doing this is tricky and benefits are small.
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