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  #1  
Old 02-22-2004, 09:31 PM
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Bosch Spark Plugs for 280SEL 6CYL

I need a new set of spark plugs for my 1970 280SEL with the straight six. It all started when I filled up at a gas station other than my usual and took on a full tank of 92 octane. These guys typically have the next best fuel in town, but I started having problems. The engine started missing a day after I filled up. I found the #3 spark plug, a Bosch Super, age unknown, to be completely fouled to the point where a carbon bridge formed across the spark gap. At the advice of a local mechanic, I went to buy a replacement set of spark plugs based on the statement that "spark plugs can no longer be cleaned." I installed 6 new AutoLite spark plugs from NAPA ( because it was all they had) and these worked for the first day. The engine was running rough the following day, so I added a bottle of Techron (because it contains Benzine) thinking that the fuel was ****, and added some Sunoco 94 to mix it and raise my octane level. Today, the engine barely ran, with two cylinders missing. I found one of the AutoLites with a heavy carbon buildup, and the other AutoLite just plain did not spark, a bad plug! Anyway, I put a pair of the Bosches back in, and it is running fine for now.

To make a long story short, I need a quality set of spark plugs that might burn a little hotter to keep carbon build-up from becomming a problem. I was thinking Bosch Platinums, and I searched the Bosch website and found the following options:

Part Number Description
4216 PLATINUM PART M130.920/980/983; Gap=.032
7500 SUPER PART M130.920/980/983; Gap=.032
W7DC SUPER PLUG M130.920/980/983; Gap=.032
WR7DP PLATINUM PLUG M130.920/980/983; Gap=.032
W7DC O.E. SPARK PLUG M130.920/980/983; Gap=.032

Question number one is: Is one of the two platinum choices (WR7DP or 4216) a hotter plug than the other?

If you can't answer that, then which plug are you using?

I have a local shop that can order me whichever one I want, so I do have some choices. Basically, I want a GOOD spark plug, so no more AutoLites. I would be willing to try Champion since they do have their insulator manufacturing plant right outside of town.

Finally, what is the correct DIY procedure to lean the mixture on the fuel injected 280SEL. I located the mixture control on the back of the injection pump, but I don't want to go adjusting blindly. In my county, there is no emmisions testing, and the car would grandfather out of it because of Ohio law. Basically, I would like to set the mixture for maximum performance, not to meet emissions standards.

Thanks a lot for taking the time to read this!
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  #2  
Old 02-22-2004, 10:36 PM
Tim's__Benz
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To my knowledge you are not supposed to use Platinums in a Mercedes. As for leaning out the mixture I don't know, but it may be the same as the 4.5. If it is then you can just turn the screw on the MAP sensor. You will find directions/pictures for this in many recent threads. If you do have this, turn the screw a quarter turn or maybe a little more clockwise. Here is a picture of the MAP.
Tim
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Bosch Spark Plugs for 280SEL 6CYL-fuel-regulator-distance-2.jpg  
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  #3  
Old 02-22-2004, 10:37 PM
Tim's__Benz
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By the way, I am just using Bosch Supers and they are giving me no problems at all.
Tim
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  #4  
Old 02-22-2004, 11:11 PM
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Well, Bosch lists the platinums plugs as a compatible replacement. I shouldn't have any trouble with the standard (non transistorized) ignition, right? According to their website, the platinum plugs require even less voltage.

As for leaning the mixture, I don't have any sensor like yours. Just an adjust screw that runs a governor on the back or the mechanical injection pump.
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  #5  
Old 02-23-2004, 10:22 AM
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hey M Anker (fellow OH guy!)

How's the flight training goin? Well, I hope.

I read a thread recently on the M-100 site wherein nobody recommended platinums, apparently results in immediate fouling with the 6.3 or 6.9 engines. Dunno how this translates to platinum use in a 6 cyl though.

Smooth landings...
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  #6  
Old 02-23-2004, 11:24 AM
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M_Anker,

You are correct...the mixture control is on the back of the pump. Only trouble is, I don't remember which direction you need to go, in order to lean it out. I'm guessing you will figure it out quickly, should you go the wrong way.
Thing is, is I believe there is a thermostat type of device on top of the injection pump...if it is out of whack, it could be making it run rich too. From what I remember, it's a rather delicate part.

forget the platinum plugs...go OEM

Good luck!

-Larry
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  #7  
Old 02-23-2004, 03:24 PM
Tim's__Benz
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Quote:
Originally posted by M_Anker
Well, Bosch lists the platinums plugs as a compatible replacement. I shouldn't have any trouble with the standard (non transistorized) ignition, right? According to their website, the platinum plugs require even less voltage.

As for leaning the mixture, I don't have any sensor like yours. Just an adjust screw that runs a governor on the back or the mechanical injection pump.
Bosch will list that. The Platinums are more. I have heard from many people on this forum that you should not use Platinums in any old Mercedes.
Tim
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  #8  
Old 02-23-2004, 06:04 PM
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Quote:
Bosch will list that. The Platinums are more. I have heard from many people on this forum that you should not use Platinums in any old Mercedes.
Well, I asked my father about it since he has a '68 280S, with practically the same engine except for a carb rather than injection. He is running the Bosch Platinums in his without any problems. I can't see why Bosch would sell the plugs if they didn't work well in the cars. How much more would it cost to tool up for production of a 30 year old Mercedes spark plug just to make Platinum? If it didn't work well, then why take the trouble to make the things?

Anyway, I told my parts guys to order them for me. I'll report back on how they work compared to the Bosch Supers that were in there. I'll probably regret it, but I can't find a definitive post in this forum to say otherwise.

I did change the oil back to old fashioned dino oil today. I think the detergent qualities in the Valvoline Durablend semi-synthetic might have removed the gunk holding my valve seals tight. It's back to Castrol GTX 10-30.



Quote:
How's the flight training goin? Well, I hope.
Still waiting for the field to dry up. I'm based at a grass strip, so I can do very little flying in the winter. On the good side, the ground is going back down so I can get the hangar doors open. I think if we go about a week without heavy rain, then I should be able to get up.
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  #9  
Old 02-23-2004, 07:05 PM
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Quote:
Originally posted by M_Anker
Anyway, I told my parts guys to order them for me. I'll report back on how they work compared to the Bosch Supers that were in there. I'll probably regret it, but I can't find a definitive post in this forum to say otherwise.
Actually, I came across a set (8) of used (but like new) Bosch Platinums, so I cleaned them in solvent (wasn't really much to clean) and I checked the gap, ready to put them on, and I did a "search" for platinum plugs.

The reason why you should NOT use them is this: The W7DC is a copper-core, non-resistor plug. The WR7DP is a resistor plug (hence the "R"). However, the ignition system is designed for NON-resistor plugs - the spark plug boots have 5k ohms of resistance built in, and the end plugs (that go on the dizzy) have 1k of resistance built in! Adding a resistor spark plug to this setup is like using resistor-wires... weaker spark, fouling plugs, poor economy, and hard starting!
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Old 02-23-2004, 10:00 PM
Tim's__Benz
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I knew it. The detergent oil is better. You should stick with that.
Tim
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  #11  
Old 02-23-2004, 10:06 PM
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If you're refering to the durablend: Yes, you should! If it cleaned gunk you think was "holding your seals tight" it probably also cleaned your rings, and a ton of seals, oil passages, etc!
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1999 Chrysler 300M (Click for pic) - 207,xxx - totalled by Nationwide for $1600 in damage. Being rebuilt better.
2014 Jeep Grand Cherokee Limited (Click for pic) - 32,xxx

My Mercedes Benz 108 109 resource site
August 2014 newsletter live.

Previous: 1972 280SE 4.5 "Quicksilver", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
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  #12  
Old 02-24-2004, 12:10 AM
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Quote:
Originally posted by Larry Delor
M_Anker,

You are correct...the mixture control is on the back of the pump. Only trouble is, I don't remember which direction you need to go, in order to lean it out. I'm guessing you will figure it out quickly, should you go the wrong way.
Thing is, is I believe there is a thermostat type of device on top of the injection pump...if it is out of whack, it could be making it run rich too. From what I remember, it's a rather delicate part.

forget the platinum plugs...go OEM

Good luck!

-Larry
Don't adjust the injection pump while the engine is running. Turn the adjusting screw one notch at a time.

If you do adjust it wile running, by mistake, it will be totally screwed up.
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Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.
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  #13  
Old 02-24-2004, 12:19 AM
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Quote:
Don't adjust the injection pump while the engine is running. Turn the adjusting screw one notch at a time.
'

Yeah, I already read that in one of my shop manuals. The thing I need to figure out is how far the screw needs to be turned. I'm looking for maximum performance and to keep the spark plugs from fouling.

Quote:
If you're refering to the durablend: Yes, you should! If it cleaned gunk you think was "holding your seals tight" it probably also cleaned your rings, and a ton of seals, oil passages, etc!
Now, are you saying that I should keep using semi-synthetic and let every seal leak, or use regular motor oil. I've heard arguements from both sides, and the consensus seems to be to run standard oil in an older engine. Now if I just overhauled it, I would run full synthetic, but I don't have the time and money to do that.

What I don't understand is how this one guy I know can keep Amsoil full synthetic in '60's vintage Chevy corvairs!
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  #14  
Old 02-24-2004, 12:30 AM
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Well, USUALLY what happens is that it will leak from the seals, but the seals will become softer and more pliable as if they were newer, and will hold the leaks further. This usually takes about 3 oil changes, though. But if your engine doesn't get that hot, or you don't push it that hard and change the oil often, dino SHOULD work fine... just be dirtier
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Current:
1999 Chrysler 300M (Click for pic) - 207,xxx - totalled by Nationwide for $1600 in damage. Being rebuilt better.
2014 Jeep Grand Cherokee Limited (Click for pic) - 32,xxx

My Mercedes Benz 108 109 resource site
August 2014 newsletter live.

Previous: 1972 280SE 4.5 "Quicksilver", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
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  #15  
Old 02-24-2004, 05:27 PM
Tim's__Benz
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I have heard that it is better to use full synthetics on older engines. As soon as I get my oil leak fixed, I am switching to full synthetic. WANT '71 280SEL has a '79 300SD and he uses full synthetic even with a very bad leak. It has helped his car run better and cleaned out the engine.
Tim
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