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spark plug BOSCH F8DC4 vs F8DC0

48K views 170 replies 25 participants last post by  GreenT 
#1 ·
Guys do you know which of these plugs are better for my 500SEL
i would assume they are pretty much same just some temperature difference depending on your climate...
My car has a sticker with F8DC0 under the hood but most of the online shops recomment F8DC4

Anybody knows whats better?
 
#2 ·
Don't know anything about those numbers but I have the Champion EONs in my 500. Haven't had them in long enough to comment. One thing I do know though is that Benz lumps seem to run really hot. It's the only brand of car I have had that builds up so much heat under the bonnet that when you open the door to get out it's almost like you get engulfed in a big invisible cloud of hot air. Now although the block should run at a set temp, I'd say bear that in mind.
 
#4 ·
Resurrecting an ancient thread... F8DC4 is the standard plug with 2.6mm center electrode, these are commonly available from the dealer or from some aftermarket vendors.

Bosch F8DCO plugs have a larger 2.9mm diameter center electrode. I believe these plugs are NLA and have been out of production for quite a while. MB superceded them to F8DC4. I think the F8DCO were MB # A0031593003.

Remember to ONLY use non-resistor plugs, especially for 80's/90's engines with EZL ignitions & distributors. F8DC4 are correct, FR8DC/FR8DC+ are wrong, no matter what the cross-reference or catalog says. If your mechanic insists that resistor plugs are fine, get a new mechanic. And never, ever use fancy-electrode plugs (platinum, iridium, yttrium, etc)... the older MB engines really dislike those.

While we're on the subject, open up the gap from the factory spec of 0.8mm to 1.0mm on the F8DC4 plugs. This can help eliminate the intermittent hot idle hiccup.

Misc spark plug photos are at this link.

:sawzall:
 
#5 ·
Great Advice About Plugs!



Dave, thanks for posting this info. Pics are wonderful.

So many folks just don't "get it" when it comes to plugs. I'm having a discussion over in W124 about this, too. Champions in a Benz? Seriously? Who does that? A 60 cent plug in a $50-100K vehicle? :confused:
 
#7 ·
FWIW, I have used iridium plugs in a number of old MB motors M114; M115 & several M119's as well as Volvo 6-cyl alum block B6304's without any problems at all.

Indeed, M119 motor went to iridium plug in'98.

Everyone is entitled to opinions, but sharing about basis of opinion is more important than the opinion.

Iridium is a very unusual element that extremely resistant to ablation by the electrical arcing while still being a pretty fair electrical conductor with resitivity about 3X of copper & 2X of aluminum. What iridium brings to the party is the ability to make very tiny exposed electrode which also has extremely long service life.

Anyone who has experimented with high voltage 10-50 kV knows that making the point of the electrode smaller makes it easier to get an ionizing plasma going at lower voltage.

The iridium allows a much smaller electrode, arcs at a lower potential. The tiny exposed electrode stays cleaner, has better duration of arc and lasts longer.

I've been using the NGK iridiums for years. The plugs can easily last 50-70 kmiles; look good and have the gap measure 1.2-1.3X the initial setting.

The only downside to iridium for this application is that it is extremely brittle matl. One has to be very careful to not break the electrode in gapping.
 
#10 ·
Iridium

daidnik,

Thanks for the information. you make some excellent points. I can see an application for iridium, I just don't know if gasoline and oil engines are suited to small electrodes and long service life. Natural gas fired emergency generators would be one application, however.

My limited experience proved to be a disaster, fouled those Bosch iridium plugs in under 100 miles. I honestly forget what vehicle I put 'em in, maybe an older Benz. It may have been bad valve guides/seals, who knows? :crybaby2:

Anyway, I pull plugs every 15-25K to see how the firing chambers are functioning. I want to see wear, i want to see color, oil, fuel, whatever on the plugs. To be safe, I use what the dealer suggests, and if the owners manual suggests more than one option, I go with the Bosch. I never had an issue with Bosch copper plugs, call me an old fashioned, last century dinosaur.

I haven't touched my new to me '99 S420's engine yet, and you mention the iridium plugs are spec'd for the M119 engines '98 models. This should be an interesting experience for this old dog**shakes head**.

Hamada,

The dealer offered you Champions? I'm eating my hat as we speak! Ha, ha, ha. :wave:
 
#12 ·
Yttrium

Ok, you fellas got me looking up this spark plug stuff.

Bosch F9DOC is the plug recommended for my 99 S420, M119.

It's a Yttrium plug.
There are Beru and Champions listed also. I'd didn't look them up for the Yttrium application.

https://en.wikipedia.org/wiki/Yttrium
 
#16 ·
Ok, you fellas got me looking up this spark plug stuff. Bosch F9DOC is the plug recommended for my 99 S420, M119. It's a Yttrium plug. There are Beru and Champions listed also. I'd didn't look them up for the Yttrium application.
Where are you looking this up? In the Mercedes/dealer EPC, or in Bosch catalog?



@LogicalPosition, The dealer didn't give me options to choose from. I told them i want to order plugs for my W201 and they gave me the plugs inside Mercedes logo box which had Champion plugs in it.
For my W140 S320 I ordered some plugs from Clark and it was Bosch plugs inside the MB packaging.
Mercedes offers factory plugs from several different manufacturers, typically Bosch, Champion, and Beru. There are different part numbers for each but are all interchangeable. Depending on price and availability, you may receive any of the 3, unless you ask for a specific brand / part number.



I had slight hesitation on idle before and i still have it now :(

I did not check the gaps on spark plugs, but they come preset usually. At the time i did not know about increasing a gap to 1.0, is it worth trying?
Yes. This is easy and free. See if there is any improvement with the gap at 1.0-1.1 mm.



Bosch spark plug wires are purchased and going in next... But still is it going to fix it? And if not what a hell is it? Engine sounds perfect pulls hard, no any other issues.
It is very unlikely that new wires will fix it. However, you can measure the resistance of your old plug wire ends/boots. Spec is ~2000 ohms and if they are within about 20% of spec they are ok. If you find any that are very high (say, 5k-10k ohms, or higer) that could be part of your problem. Assuming your new M119 wire set is the type with orange plastic plug boots and light gray wire, be VERY careful laying the wires into the plastic X-tray. The gray insulation is fragile and tears easily. This won't affect performance if it tears, but you'll feel better if you don't damage them in the first place. The X-tray has numbers on the bottom which tell you how to route the wires, they should all fit neatly in place. But the aftermarket wire lengths probably won't match OE, so you'll need to get creative to make everything fit nicely...





 
#13 ·
I was wrong about the plug change in '98 for M119. Change was to laser welded platinum electrode. Design principle was same as with iridium ... reduce electrode area for arc ignition while retaining longevity. It doesn't seem like Bosch grabbed on to iridium for consumer vehicle application, but they have a line of industrial engine plugs using iridium on both electrode & ground.

Interestingly enough iridium has melting point 1200 deg F higher than platinum. NGK was issued a patent for the basic idea of the iridium tipped electrode and/or ground electrode in 1988. I think the really dark art to the use of this matl is in the method of joining metals with widely differing melting temps.
 
#15 · (Edited)
As long as all ignition specialists are already on this topic... :)
I'd like to pick you brain a little:
I just replaced rorors and distributor caps and all spark plugs. Specified bosch plugs no resistors, as recommended. old plugs were ok, but a bit darker then they should be, looks like they were changed once over 60k. 2 plugs were not tight for some reason. I had slight hesitation on idle before and i still have it now :(

So, any ideas what may cause it? Engine is running fine on any rpm but idle, if ac is on hestitation is not there. It is very minor, you can hear slight miss every 30-40 sec.

Bosch spark plug wires are purchased and going in next... But still is it going to fix it? And if not what a hell is it? Engine sounds perfect pulls hard, no any other issues.

I did not check the gaps on spark plugs, but they come preset usually. At the time i did not know about increasing a gap to 1.0, is it worth trying?

Ah also, i drive and then stop, hesitation will not be there, as well as if i race the engine it will give me couple minutes of clean idle. If it sits ide for some time, then i can feell it, again very slight.
 
#21 ·
I used the Bosch F8DC4 plugs when I changed mine but was surprised to find the old plugs were RF8DC4?? I forget the exact miles, but service records indicated more than 90,000 on them. The car had run and idled smoothly with them until I had a "no start" issue after it sat out in a very heavy downpour.

I also changed my plug wires(to NGK) and coils(Bosch). 8,000 miles later, everything remains at extreme power and an idle so smooth you cant tell the engine is running. Don
 
#22 · (Edited)
Under load and in any conditions (besides warm idle no AC) it is smooth. So your second statement is the exact description. Engine mounts are brand new 30 days old :)
Anything else i should check? So far i have bigger gaps and wires in troubleshooting list.

Caps and rotors are done already, harness is new, throttle body -eta has not been re-wired yet. But it seems to work so far.
 
#28 ·
The M119 factory manual implies that the EZL could be damaged over time, if the secondary ignition system has higher resistance than normal. A typical resistor spark plug measures around 5k ohms. If MB said not to install 5k ohm rotor arms, I would presume they also would not want 5k ohm added at the spark plugs either. See attached screen shot from FSM. Source doc is job 15-0100 section B (click here).

Note this was specific to the M119, I don't know if other engines/EZL's have the same concern. Later engines with distributorless coil-on-plug ignition can probably use resistor plugs, although I still wouldn't do that if it wasn't factory spec.

Shameless plug: I sell Genuine MB F8DC4 plugs via eBay. Yes, you can get aftermarket ones cheaper, and yes you can probably get the OE plugs cheaper if buying other stuff from an online dealer to offset shipping costs. But if you just need 1 or 2 sets of OE plugs and not a bunch of other stuff... click here.

:grin
 

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#32 ·
i agree with what you wrote. i wrote similar thoughts here not so long ago. from what i have read and studied i made a final conclusion that using resistor plugs in our cars cannot make any harm to the ignition system/engine. I use resistor iridium plugs i believe (i forgot details) but definitely not a copper ones. it was en experiment due to slightly rough idle but later i kept them in the car.

You confirmed my hypothesis that spark is much stronger in plugs with smaller tips due to smaller surface where electrons travel in comparison to copper plugs with larger tips. I have never read this explanation anywhere.
 
#33 ·
Researcher at Bosch is correct, old books are NOT. That easy!
Platinum and iridium plugs are better, resistor is irrelevan in this case.
Flame front distribution and burning stability is much better with modern iridium and platinum plugs.
Goodle exlanation at NGK and Denso sites. Multiple electrodes is gimmic never delivered technology.
Best plugs are NGK and Denso doublr iridium, they have the smallest electrode size and allow for better igniting of the mixture, also watch compyter simulations on youtube.

Bosch quality is all over the place nowerdays, i cannot recommend.

Engineers spend countless ours and came up with exitic metals fir the electrods for a reason... they are not dumb... old syle plugs are ok, but new ones times better.
Once again resistor us irrelevant in thus case, speaking from personal experience, non-resistor bosch was running much worce in my car then platinum NGK :)
If you have shaky idle, spark plugs, caps, wires, o2 sensor are first suspects...
 
#35 ·
Like here, we've had this spark discussion ad nauseum at the W126 forum but it always comes back to how the engineers designed our ignition systems and why on earth would a layman want to question/change that.

MB was/is a premium brand and when FM radio became available sound quality was very important along with luxury and performance. It is true that previously all plugs were non resistor types because there was no need for them to be otherwise...




At the moment the spark jumps the Gap it causes a high frequency burst of energy, known as RFI (radio frequency interference). RFI, as its name suggests, creates static on your radio and interference with other electronic equipment, including the vehicle’s on-board electronic control units (ECUs).

Resistor plugs were developed in the 1960s to suppress some of the spark energy, thus lowering RFI to an acceptable level. Most Resistor spark plugs use a monolithic Resistor, generally made of graphite and
glass materials, to filter the electrical voltage as it passes through the Center Electrode.

Since Resistor type plugs actually “resist” some of the spark energy, non-Resistor type plugs actually deliver a more powerful spark. It is for this reason that most racing plugs are non-Resistor types. However, in most automotive applications, a Resistor plug is required for proper vehicle operation. Use of non-Resistor plugs in
vehicles that call for a Resistor type can result in rough idling, high-rpm misfire, and abnormal combustion.

https://www.sparkplugs.com/glossary/8/spark-plug/R


From the M119 manual...





Btw, the EZL is a pretty sophisticated (for the time) integrated circuit that can easily be fried if the wrong voltage, plugs, wires, coils are used. See this thread for more info...

http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1615090-heres-list-ezl-modules-pics-part.html

http://www.benzworld.org/forums/w12...ist-ezl-modules-pics-part-2.html#post16948522


YMMV.
 
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