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Discussion Starter #1
After doing some research, I want to find the correct non-resistor spark plugs for my 1990 300E 3.0 L, M103 engine.

I called my local MB dealer here in Canada, and the parts guy said the Bosch plugs are $26.17CDN each - yes each, which works out to about $20.15 US each!
The dealer said the the BOSCH plugs were H8DCO. Are these the correct plugs for my car? I thought they were supposed to be H9DCO.

Apparently NGK BP6EFS are supposed to be good ones. Does anyone know where I can buy these?
 

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There are two plugs that meet spec for the M103. Besides needing to be non-resistor, cooper core plugs, they need to have a beveled/tapered seat. Both NKG BP6EFS and Denso T20EPU's meet all factory specifications. You will find these plugs from online sellers. Amazon for the Denso's and ClubPlug.net for the NGK's.

Bosch F8DC4's do meet the criteria of being non-resistor and copper core, but have a gasketed, flat seat. Some folks either leave the gasket in place or cut it off. The Bosch plugs are usually less than $2 and available from sources like AutohausAZ, FCPeuro etc.

Personally, I use the correct plug for the M103 head.

Good luck

Jayare

Sent from my XT1710-02 using Tapatalk
 

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Discussion Starter #3
There are two plugs that meet spec for the M103. Besides needing to be non-resistor, cooper core plugs, they need to have a beveled/tapered seat. Both NKG BP6EFS and Denso T20EPU's meet all factory specifications. You will find these plugs from online sellers. Amazon for the Denso's and ClubPlug.net for the NGK's.

Bosch F8DC4's do meet the criteria of being non-resistor and copper core, but have a gasketed, flat seat. Some folks either leave the gasket in place or cut it off. The Bosch plugs are usually less than $2 and available from sources like AutohausAZ, FCPeuro etc.

Personally, I use the correct plug for the M103 head.

Good luck

Jayare

Sent from my XT1710-02 using Tapatalk
I have also read that perhaps I should be using NGK BP5EFS instead of BP6EFS as they run hotter. Do you recommend the BP5EFS instead of BP6EFS? And do you know if my MB dealer gave me the wrong plug (H8DCO)?

Thanks
 

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BP5's are one range hotter than the 6's and would help if you have oil burn issues. I do not know the specifics of the plug the dealer sold you, but for $20 a pop they need to be magic.

Sent from my XT1710-02 using Tapatalk
 

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Hi,

because I had problems with the Bosch Plugs in my 300 SL /R107 with M103 in the past, I use since about 6-8 years the NGK Brand and I am very satisfied.NGK BP 6 EFS Number 3812

Best regards from Germany
 

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I've been using the Denso plugs for a decade now....great plug. You need to check your plugs though around 15-20K. They don't last 100K like in modern cars....they do wear out.

I bought a bad lot of NGK plugs for my small engines and so I boycott them now....but YMMV.

Kevin
 

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I was informed after making enquiries about a set of 6 spark plugs for my M103 on a very good web site called The Green Spark Plug Company in uk They told me that Beru spark plug number - Z7 is recommended for the M103 .And at that i purchased 6 from them . And thats what i have been using for the last 12 weeks . .Used NGK and Bosch in the past but this service i just wanted a change to go with the new set of Beru ht leads i fitted .
 

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Discussion Starter #9
I called up another local MB dealer here in Metro Vancouver, they said they have H9DCO for $13.14 each ($10 US) - still too much for plugs.

I will be putting in a new Bosch distributor cap and rotor as I have existing Bosch ignition wires that are still good. I will go for the NGK non-resistor plugs - I don't think I should have an issue with them even though everything else is Bosch.
 

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I have also read that perhaps I should be using NGK BP5EFS instead of BP6EFS as they run hotter. Do you recommend the BP5EFS instead of BP6EFS? And do you know if my MB dealer gave me the wrong plug (H8DCO)?
plug temp ratings are a funny thing. a 'higher temp' aka 'hotter' plug is designed to run in a hotter environment, and dissipates heat faster, so it runs cooler. a 'cooler' plug in a hot engine will run too hot and not cool sufficiently, this will accelerate electrode erosion. conversely, a 'hot' plug in a cool engine will be more prone to fouling.

MB specs a "hotter" plug in .EU where people are more likely to drive at high RPMs for extended periods, and a 'cooler' plug in the USA with our ridiculously low speed limits and a majority of trips of only a few miles.

also IIRC, NGK temp range numbers go the opposite way of Bosch.
 

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Discussion Starter #12
I was just checking Clubplug and they do not have either BP6EFS or BP5EFS - they only have BP6ES and BP5ES (No "F" so apparently not Tapered). Are these acceptable?

And I see that MercedesSource is also selling a set of NGK non-resistor plugs specifically for the M103. The part number is not listed - has anyone bought these from MercedesSource or know what type he is selling?
 

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what is the proper torque for the spark plugs on a 1987 300E.

I am changing them now and in the past never used a torque wrench but figured I would now

Thanks
 

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Hi

I just replaced the plugs with H9DCO. I had platinum ones installed.

The car is burning alot of oil. I drove the car alot in the last two weeks and it seems like I am consuming around 1.75 quarts in about 500 miles. This is a rough estimate based on watching it every few day.

Attached are some pictures of the plugs I removed. From left to right they are 6 5 4 3 2 1. One side of the plug was discolored a bit and the other side was mostly white, this is on all the plugs. I took two photos after rotating the plugs 180 degrees.

With burning large amounts of oil I thought they would be worse. I believe the goo above the threads is from the anti seize that I applied when I installed them.

Please share any comments as to the plugs appearance.

Plugs 6 and 4 have a maroon, or red wine type tint to them.

Thanks

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