I made the mistake ofputting platinum bosch plugs in my 87' 260E. They didnt do too well so i had a shop order me what i thought were H9DC but instead they were HR9DC. I didnt even realize until I had put them in. Will they affect or damage mymotor? DO they effect preformance? Thanks
Ben

I don't think these are good questions - for about $12 you can do it right and not worry about it.

It is an absolutly legitamate question. I want to know if they are ok? If not, I will replace them. If they are OK, there is no need to waste a set of spark plugs.

The OE plugs are non-resistor types and anecdotal evidence indicates that resistor plugs can cause idle and/or emissions problems.

The OE plugs had a "heavy duty electrode" as indicated by either a zero or "oh" suffix (I forget which) as in H9DC0. These can be found at Mercedes parts specialists such as Fastlane and probably dealers, but they are more expensive than the standard electrode H9DC.

The "R" prefix in your plugs indicate that they are resistor type.

Non-resistor plugs are rarely stocked by parts stores or repair shops unless they are Mercedes specialists, and although correct non-resistor types are supposedly made by both Champion and Beru in addition to Bosch, I have never found anything other than the correct Bosch.

My suggestion is that you buy a set or two of H9DC from Fastlane and give them you your mechanic to install when they are due for replacement at 30K miles. Most commercial shops will just install a resistor plug, which is not correct.

Correct spark plug replacement numbers are in your owner's manual.

So that's the deal. Whether you chose to install a proper OE recommended plug or continue with the incorrect installed resistor plugs is your call.

Duke

They won't damage your motor. They may sputter a bit at idle if they get fouled. Your spark plug wires have resisance built in and RF supression shields on the plug boots. That makes resistor plugs redundant. But not evil.

Plugs are cheap and easy to get to on a 260E. They're also easy to clean. If your car's running fine with the ones that are in there, I'd leave them, but I'd also have a set of correct plugs to swap in if the engine starts running rough. With electroninc ignition, they should last a long, long time.

Enjoy,

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Norm in NJ
Next oil change at 230,000miles

Does anybody know what is the R plugs' average Ohm resistance compared to the wires.
Is it a case of few ohms in the plugs and few thousand in the wires.If that is the case,R plugs probably wont make much difference.?????

I've using TR5 NGK plugs 3-yr old now as suggested by some indy on alt.auto.mercedes LYnda Jantzen???? if memory serves

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Tom 2010 C250 4-matic Sport (Canada)

On many plugs I have tested, the average resistance seems to be bout 5 k ohm.

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2007 C 230 Sport.