Reading the spark plug issue of Marineboy0 caused me to think about spark plugs. I use Bosch Platinum +4 spark plugs in my V12 and have had no problems with them. The performance improvement is subjective, but I think they are better than the standard MB single-pole spark plugs. You can review the Bosch offering at…
http://www.boschusa.com/AutoParts/Sp...PlatinumPlus4/

Hoping to generate some discussion about spark plugs… So, what do the rest of you use and why do you feel your plug of choice is best?

 

YOU SHOULD NOT USE RESISTOR PLUGS ON MERCEDES!!! The ignition system is very carefully designed for use with non-resistor plugs. Resistor plugs add secondary resistance is excess of design specs and alter the secondary voltage wave form.

Sooner of later you will have problems such as rough idle or high emissions.

The proper plug is Bosch H9DC (NOT the HR9DC resistor type), and these are not commonly available at McParts, but are readily available for two bucks each from Mercedes parts specialists like Fastlane.

Any spark plug with an "R" in the designation is a resistor type and should NOT be used.

The issue is not "platinum" versus conventional copper core plugs. It's resistor versus non-resistor and Bosch Platinums HAVE RESISTORS.

Take a look at the service CDs. They have several examples of both normal and anamolous of secondary wave form traces and show at least one with excess secondary resistance. It may not result in any noticeable difference when the plugs are new, but as they age - wear and build up deposits, the number of misfires will increase resulting in more idle roughness and higher emissions than if the proper non-resistor plugs are used.

Bosch H9DCs (for M103 engines) cost about two bucks each and have a normal service life of 30K miles. The H9DC0 has a "heavy duty" electrode. They were OE, but they are more expensive, and the standard electrode H9DC work just as well over the 30K service interval.

Spending more money to by the WRONG plug is just plain foolish!

 

Thanks for the information TresX. As noted in the other thread, I will be researching and performing some side-by-side comparisons.

 

I see no advantage in multiple ground electrodes. Only one tip is used at a time and the extra ground electrodes can only hinder heat dissipation since they obviously block the path of spent gasses from around the ceramic core. This may be/probably is taken into account with their design but remains a problem the single electrodes do not have. With unleaded gas and today's engine management systems plug wear is minimal and I doubt the extra ground paths are ever used or needed by the spark. Anyone ever take one out after 50K miles and check? Besides, I have yet to have a platinum plug wear beyond its' adjustment limits during its recommended replacement cycle. Also....despite what plug manufacturers would like for you to believe...there are no direct replacements between brands with respect to heat range. They are only close. Unless you have an abnormal driving environment (close to 100% city or 100% high speed highway) you should stick with the recommended heat range and plug manufacturer.

 

TresX - I am intrigued by the extreme belief you have relative to non-resistor vs. resistor plugs. I appreciate your thoughts however I am having difficulty finding information; either in MB documentation or the Bosch Engine Management Manual that even discusses the subject. Could you provide more details as to the documentation you are referring? It’s not that I do not believe you; I simply wish to research the information myself; to establish my own understanding.

Your explanation, at least at face value does not make sense… at least from my electrical engineering background. The most important point aspect of the spark plug is to create an arc at the exact instant the engine management program stipulates. An electrical arc is created by “jumping a gap” with a very high voltage potential. Not trying to insult your knowledge, but only wish to reiterate the plug’s purpose.

A resistor-type plug CAN cause a degradation of current flow at the very instant of spark generation – this is true. As we all know, this is the basis of resistor plugs in the 70’s to greatly reduce the infamous radio “static”. Today’s electrical systems are far more immune and non-resistor plugs can be used with confidence and a clear radio. But my engine does seem to perform better with the Bosch 4-electrode version.

So what’s the big deal with the Bosch four-electrode model, resistor or not? I believe the four electrodes do provide a higher chance of the spark arc occurring precisely when the engine management program wants it to. Four times as much, per spark event. If, for example, the “primary” arc gap has (for whatever reason) a resistance, there is another gap that would arc. You are correct in that only one gap is used at a time, but the gap path could be different for each arc event. One could argue that the timing difference is miniscule, and I would agree. But if the spark itself IS more consistently timed correctly, the engine overall would run a bit better/smoother. This logic is sort of portrayed in my personal findings over the last 6 months. Again, I am NOT saying the Bosch 4-electrode plug is the perfect plug… only that my data indicates a bit better performance.

Perhaps after 50K miles the plugs may deteriorate faster than the standard plug. For me at least, I may never get to that point, as I would change the plugs at the 30K mark. Not sure why, perhaps it’s simply from my old small block Chevy days with 4-barrel carbs.

Regardless, I will be changing out the Bosch 4-elctrode plugs this week in favor of fresh MB plugs. I also have a set of slightly used MB plugs, but I am unsure of how many miles are on them.

Thanks TresX and mleskovar for the thoughts, and I would be interested to hear more of your opinions/thoughts, as well as others.

 

When the spark initiates a tiny flame kernel, the spark plug electrodes represent a BIG COLD HEAT SINK relative to the 4500F temperature of that tiny flame kernel, and the flame can be quenched by a big heat sink, which results in a misfire.

"Fine wire" electrode plugs - usually "double platinum" - both the center and fine wire ground electrode can be advantageous in high performance engines with marginal ignition energy, but this harks back to the days of mechanical breaker points. Modern electronic systems going back to the seventies have at least double the per spark energy of breaker point systems. I've seen plugs come out of mid-seventies GM products with HEI systems where the center electrode was worn nearly to the insulator and you had to measure the gap with a ruler, but the engine basically ran fine. When you have a "fancy" ignition system, you don't need anything more than a plain vanilla two-dollar spark plug.

So conventional electode plugs work very well with modern ignition systems. These Bosch Platinum plugs that are heavily advertised and sold at McParts are junk and defy every theory of ignition and flame propagation because all those ground electodes are a HUGE heat sink to an incipient flame, so there are going to be more misfires, which eventually means rougher idle and over the limit HC emissions.

Measure the wire resistance on your engine, all will be about 2K ohms regardless of length. My understanding is that the wires have discrete resistors that are part of the spark plug terminal, so the wires themselves probably have very little resistance. It's also my understanding that the cap has resistors - about 1 or 2K ohm - built into each cap terminal.

Mercedes implemented a unique solution to the RFI suppression requirement. Rather than using conventional resistor spark plugs and RFI wires they have discrete resistors built into the spark plug terminals, cap terminals, and require non-resistor plugs to achieve the design secondary voltage wave form.

If you use anything other than Mercedes OE equivalent spark plugs, spark plug terminals, wire, or cap you're asking for trouble.


As far as where is all the documentation for all of this? Get a subscription to Star magazine. They have an artilce almost every month where the technical editor writes of how these platinum plugs are NO GOOD!

Anyhow, this will be my last ditch effort to convince you. I appreciate your background in electrical engineering and I'm sure you're a very intelligent person, but from my experience with "AUTOMOBILES" you are incorrect.

Honestly, if you needed open heart surgery would you go to a surgeon or a micro-biologist?

 

Thanks TresX for your thoughts on the heat sink aspect of spark plugs. Yes, the larger mass of ground electrodes in the 4-electrode plug would present a “cooler” area for the instant flame to overcome – especially when cold. However, the mass would come to temperature and remain fairly constant after the engine is warmed.

For the benefit of others reading - at a mere 1,000 RPM (a little over idle), each plug is firing over 8 times per second. At modest highway speeds (well, at least in California) my engine is near 2,500 RPM, which equates to each plug firing over 20 times a second. That’s a lot of heat being generated and being absorbed by the plug’s electrodes. One could debate that the extra mass of electrodes may assist in keeping the plug cooler under highway conditions. Regardless, I want to research the heat sink thought some more.

Because my engine has distributor-less ignition, I do not have the traditional high-tension wire found on most engines. Instead, I have coil packs; one per spark plug. However, the concept of the coil pack is identical to that of traditional distributor engines, just without the mechanical aspects of distributors. I have always been curious about what EXACTLY is inside the infamous coil pack. May go to a junk yard, scavenge an old one and tear it apart. I would like to see what amount of resistance is in the short high-tension connector, as well as the energy coil itself.

As for whether the over-advertised Bosch plugs are junk or not, I can not say… yet. One must admit that MB way over-emphasizes the concept of using ONLY Mercedes-Benz parts; that all other parts are inferior, cheap, junk and will cause problems. Remember when synthetic oil first came out? No auto manufacturer would sanction it. Now MB demands it. (Granted, synthetic oil has improved over the years.) It all hails back to the advertisement picture of the MB Engineer hunching over with a migraine headache at the instant someone in America used a non-MB part.

TresX, I’m not trying to convert you or change your mind, or anyone else. I am merely seeking different thoughts from different people; sharing ideas and concepts – nothing more. True, I am not an automotive engineer. But I have far more years of automotive experience than perhaps you give me credit. I also do not subscribe to the MB-only parts philosophy simply because the marketing folk in Stuttgart say so. This is why I want to see/experience different aspects and not accept blindly what the OEM says. If my experiences prove to be not as good as the OEM, then of course, I will follow the OEM's recommendation. Also, I have been a member of the Mercedes Benz Club of America for many years and have all the back issues of the Star since I joined. While I do not recall a specific article in the Star regarding different spark plugs, I will look for it. In the meantime, thanks for the discussion and your thoughts; sorry we cannot continue it. Any thoughts from others?

 

Actually before I end, let me clarify a little further. The argument here is not Bosch vs MB parts. (OEM MB plugs are either Bosch or Beru) Neither is it platinum vs copper. In fact all M112 M113 engines and come OEM with Bosch SINGLE electrode platinum plugs. The arguement is Resitor vs Non-resitor and single electrode vs 2,4 electrodes. Obviously we disagree on what we know and believe. By the way, I in no way am doubting your knowledge in automobiles. So, I'm just gonna put it this way..... MB spends millions in R&D to manufactur these engines and to get the maximum performance out of them. Do you honestly believe that, even with your extensive background in electric engineering, that they didn't think/know about these type of plugs when they built the engine? Of course not! They built their engines to work specifically with the plugs that come with the car! SO.....why would you want to put anything else that wasn't inteded for your car? You have to remember that we live in a society where manufacturers will make all sorts of claims based on biased data, they put together in their own facilities, to turn a profit. Don't you remember those ab belts? Or more relavent, that tornado thing that gives better MPG? Wouldn't manufacturers have put these things in their cars since it came to be 8+ years ago?

I'm not saying that these plugs are completely worthless. Just not what is intended to be used in our vehicles.

 

Thanks for the chuckle... Ab Belts and Intake Tornados!!!! How about the *water* injection system from the late 60’s?!? Yes, I remember them all, and you are correct - there is a lot of junk out there. But innovation comes through different thoughts. And we must think for ourselves, not through corporate eyes. If memory serves me, the infamous flexible fan blade was an after-market success before auto makers adopted it as standard equipment. There are good ideas out there; we just have to separate the good from the bad.

Yes, the discussion is on resistor vs. non-resistor and multi-electrode spark plugs. I'm still researching and it may be that my research shows the resistor to be more of a liability than the gain by using multi-electrode. Who knows, I may be an innovator. Then again, I may be chasing the spark plug version of an "Intake Tornado". But it is fun to challenge the traditional thought and "think outside the box". Thanks again for your thoughts and the great thread!

 

I agree that the issue isn't buying replacement products from MB. Just equivalent/recommended parts. As far as resistor vs. non resistor plugs is concerned I have read the results of an electrical engineer who plotted the spark coming out of our single cylinder 4 stroke classic motorcyles at the plug with an oscilloscope. Adding resistance decreases the dwell of the spark peak. Peak/voltage remains the same but for a shorter amount of time. Helps with electronic and radio interference problems.

 

It may be my imagination, but do multiple tips defocus the electrical field needed to produce a healthy spark? I'm thinking that the ideal spark electrode would be two needle points at the proper gap. Is there any truth to this statement?

 

No, the electricity will always take the path of least resistance. There are sparkplugs somewhat like you suggested and there are plugs with no 'tips', just a ring around the core providing the ground. And many types in between. The actual gap isn't as critical as most people think....critical being to within .001" Often you'll see accceptable wear limits of up to 15% of the recommended gap. Multiple tips do provide a new path for the spark to take if the one currently being used wears beyond another tip gap clearance. But with unleaded gas and clean burning engine technology they do not wear like they use to. Anyone disagree? Disclaimer: I am not an EE, ME, CE or a physicist.

 

Mleskovar, you are correct about multi-pole electrodes – the arc will take the path of least resistance. This is the advantage of multi-electrode spark plugs, in that the arc has a greatly improved chance of firing exactly when required with multiple possible paths.

As for the gap, my weekend experience proves you correct. As part of the research I am doing in spark plugs (see above), I removed the Bosch Platinum+4 plugs and reinstalled the spark plugs sold to me through the MB dealer in San Diego. Well, some interesting things were discovered…

First, the dealer SOBs in San Diego sold me the wrong plug!!!! I plan to post later more on the spark plug change experiment that is currently under way in my V12. This detail will be fully outlined.

Second, I found the gap was WAY off on every single plug… by the same amount. The owner’s manual clearly stipulates a nominal spark gap of 0.032”. All 12 of the plugs sold to me through Mercedes, and installed in my car by Mercedes, were set just under 0.040”. Folks, that’s 20% off!

The point is that the car ran quite acceptably with the 0.040” gap from San Diego to San Jose. Even gave me reasonable gas mileage, etc. Obviously, the electrode gap is not as critical as in days long passed. I have since abandoned the notion of spending an inordinate amount of time painstakingly trying to make the gap perfect.

Kestas, I do not believe it is important for street engines to have plugs with needle points. The spark arc will occur across any two metallic points – one with high potential; one with ground. No electric field at the spark plug is needed for automotive spark generation. In street applications, the spark is not required in an absolute, precise location; such as a needle point. In fact, if the plug did have needle-like points, I would think they would wear very quickly – arcing is a destructive process.

 

New math?

 

Then I'm somewhat confused on why is it recommended to file the center electrode flat during service. I thought it was for spark performance. Is it simply to aid in measuring the gap?

 

Mleskovar - Sorry, dude... old math!
0.032" / 0.040" = .8 = 80%
There is a 20% difference between the two amounts; the wider gap is 20% wider than the smaller gap. Math aside, I was truly shocked that they ran from San Diego to San Jose with a gap this wide. It really blew my current thinking of spark plug gap out-of-the-water. Just dawned on me that the statement could be read a different way... No, the spark plugs were not 20% off their price. (Wish they were!)

Kestas - I was taught that the filing flat of the center electrode is more for cleaning than "flatness". The spark plug, as we all know, starts to foul with combustion stuff. If the center electrode starts to become covered with deposits, then it makes it increasingly difficult for the spark to be achieved.

 

.040 is actually 25% wider gap than the smaller .032. Other way around, .032 is 20% narrower than .040. It is still .008" but as a ratio it changes depending on which number you use as the reference.

The gap is spark plug dependent for each application. Different plug types and brands have differing electrical and physical properties. I've seen the recomended Bosch plugs come pre-gapped at .032 while the recomended NGK are .040 for the same application.

Also, do not try to file or sand any plug except a standard copper electrode. You will damage the exotics and create hot spots. Filing a used plug would expose some fresh copper making the plug perform like new. Same goes for gapping. Be very careful not to damage the platnium/palladium/irridium/etc. electrodes.

 

wow you definitely stirred up something here. Personally I run the ones I buy from the dealership. Yeah yeah, the dealership and outrageous prices, but the 'discounted' price offsets that. And it is nice to pick up the plugs with the other OEM such as filters and what nots and not have to wait in line at pep boy and I could make a cup of hot cocoa at the dealership too :p

 

I'm thinking of replacing the plugs on our '98 E320 (103,000 miles) with Autolite Platinum Pro AUTLT (Advance Autoparts Part No. APP3924) - GUARANTEED FOR 5 YEARS AND 50k. COST: $50 FOR 12 PLUGS. Any pros or cons?

 

If you're looking to only go 50K miles with the new plugs, you can go with NGK 7090 which is around $3.50/plug and a better quality than Autolite from my experiences with non-MB cars.

By the way, is this the first plug change for your 98 E320 with 103Kmiles? I hope you can get the plugs out OK. I have an 03 E320 and I changed my plugs at ~50K miles because I heard too many horror stories of plugs seizing up in an aluminum cylinder head at the 100K change recommendation regardless of the plating put on the plugs to stop this from happening. While I was taking the plugs out, they were all squealing -- glad I changed them.

Good luck and don't forget the anti-seize paste and the dialectric grease too.

Regards,
paul...

 

Thank you Paul, for your comments. Yes, at 103,000 miles they are still the original plugs. I have been watching the fuel consuption carefully and figured that it would become obvious when the plugs began to break down. They have not, sofar. Just had a 100K 'B' service and the service center wanted $300 to change the plugs only! I told them to forget it, I would do it myself. - I am aware of the 'seizing' problem. We'll see. Maybe a few drops WD-40 first will keep the plugs from squeeking when they come out. Right now I'm more concerned about the hard to reach plugs. Will I have to remove other items in the area first, or just need a special sparkplug wrench? One more thought on the subject. When an engine is set up to fire each cylinder with two plugs, it is considered in the timing of the sparks as well, because if one plug stops firing, there is a chance that detonation will ocurr. The flame front squeezes the fuel/air mixture around the non-firing plug, (which should have been ignited earlier,) to a point where where it lets go all at once and detonates! I don't want to wait until that happens. This really is the main reason why I am going to change the plugs as soon as possible. AND still one more item. The original specs call for a spark plug gap of .032". The recommended gaps on the replacement plugs seem to be .039" as a rule. Two things come into play here, if you begin with a narrower gap, as originally called for, it should extend the service life of the plug, because the gap usually widens as the electrodes wear. And here is the second thing. In aviation it is known that a narrower gap yields a hotter spark, making ignition of the fuel/air mixture easier, especially at altitude where the ignition harness starts to 'leak', shorting out the spark before it fires. :-) Any thoughts on these things?

 

I bought the OEM Bosch plugs and set the gap according to the spec in the owner's manual (and the plug box also had the gap size). When I said that the plugs were squeaking when they came out, I meant that the two metals were scrapping against eachother -- I usually don't get this when changing plugs on other cars. MB plugs take the standard small diameter plug socket and a couple of small extensions (like 3") will come in handy for the tight spots and squeezing your torque wrench in. I removed the coil packs to improve my access to the plugs and to help me with applying the dialetric grease -- I labeled the 2 wires so they would go back on the right plugs. I used a 17mm open end wrench to pull out the boot fitting on the plug wire by leveraging off the cylinder head. The whole job took 2 hrs and I was being meticulous. I never wait until I hear changes in the engine to perform maintenance -- I either do it on the recommended interval or before. By the way, the plugs I removed at 50K miles looked great and didn't have any wear that I could see.

Regards,
paul...

 

Why so much argument? How about put one on your car? Try both of them. Forget about all those graph and reserch and all those electrical engineer back ground. That is what I did. Here is the result I found. My 1995 E320 is driven and shift smoother with Bosch regular copper non resistance plugs. Besides,I paid $1.15 for Bosch Copper as compare to $5.99 for those fancy Platinum4. Dont waste your money !

 

I agree - why so much argument? I would think the engineers at Mercedes did enough work on this issue. Heaven knows that they have enough fancy and specialized equipment and enough smart people to figure out the best plug for an application. Why reengineer something that's already been engineered? (I'm guessing it's the psychological need for people to believe that they know "better" than others. That's why snake oil products are so popular!)

I've been in enough auto supplier facilities and met enough smart people in the industry to appreciate the kind of engineering that goes into each part on a car. Regardless of the "boners" that have made their way onto vehicles (I blame management and bean counters, not engineers), spark plug choice is not something that can be easily botched.

 

You're right. Actually, when Bosch introduced those 4-prong electrode plugs I realized that I've seen these before -- I did -- back in the early 70's when I knew someone who was a small airplane mechanic. That plug design was in those small plane engines due to the high lead content of the aviation gas, so those electrodes could get coated with lead and cause misfires. I don't see that happening in today's cars without leaded gas. IMHO, it's a bunch of marketing hype!!

Regards,
paul...