mac911

2008 C300 (will help me choose for next year on my 09 SLK350 too):

Owner manuals both recommend either:

NGK PLKR6A

or Bosch Y7MPP33


The dealer has the correct Bosch listed above with Mercedes star, but $14.xx plus shipping (hour drive from me each way).

Most places have the similar Bosch with one difference: YR7MPP33 . Notice the "R." It is a resistor plug to help car's electronics. However, MB clearly doesn't use the "R" version in their engines from the factory.

Finally...the NGK PLKR6A is very hard to find, easy to find is the PLKR7A (about $11). However, that is a different temperature plug (7 instead of 6) and it seems wrong to change from factory?

The cheapest option is the Bosch YR7MPP33 (about $8 each), but again, it has the "R" in there for resistor whereas the true factory plugs do not.

What do you recommend I choose?

Thanks!!!

mac911

I ended up choosing PLKR6A for about $12 each from a speciality spark plug store online.

I really wanted to stay with a plug recommended in the owners manual.

PLKR7A could have been $1 cheaper, but I knew it's a different heat range.

Bosch YR7MPP33 is far and away the best deal, about $9 each, but Mercedes book specifically lists the non-R version, and I don't know why, even though the NGK is a resistor version.

It seems only Mercedes themselves gets the non-Resistor version.

Knightmare69

Maybe it's just the v6 + engines but my i4 turbo CGi motor uses R versions NGK plugs from the fty.

mac911

Thanks! Good to know. Oddly enough on the V6, the NGK plugs for it are indeed "R" from the factory recommendation too. However, the Bosch option are non-R.

I suspect for some reason some Mercedes cars don't require a resistor so if they can save 1 cent and get one without resistor, they do, but NGK probably tells them, we are only going to make one version.

I did read, in theory, you could lose some spark by having a R, but it would be a very minimal amount. It did say like in racing, they wouldn't have resistors.

They ended up not having all 6 of my PLKR6A, so now I'm getting the plugs not in my manual.

The R version of the Bosch, hopefully they will be ok after all. I had really wanted one of the plugs in the owners manual, but now I have to be slightly off with the R version of Bosch.


Probably no one will read this, but I did have one final question:

Should I put one bead/drop of dielectric grease on the top side of the plug before pushing the coil boot back down over it? Or not necessary? Thanks!!

C300Sport

My factory plugs were resistor versions.

Knightmare69

Well last time I changed my plugs my parts guy didn't have the OEM NGK's in stock so he gave me Bosch versions, I didn't check if they were R version or not. They work fine, I don't notice anything off about them so I guess it's ok?

mac911

Yep, you have already tested them out, so you should be all sorted. It should never be a worry I don't think, I was trying to learn more before deciding myself.


Regarding this YR7MPP33 for the V6 cars. I noticed that the only cars the YR7MPP33 fits are Mercedes-Benz cars.

Therefore, I don't see how Bosch could have messed up the YR7MPP33 by putting the resistor, it's only for Mercedes, so it's not like they installed the resistor for other applications. Oh well.

myinternetsucks

Glyn M Ruck

Mac ~ I've only ever used the standard Bosch non R in my cars. Resistor spark plugs should reduce electromagnetic interference with on-board electronics including the car's engine management electronics.

Benz used to state in the WIS that they wanted the ignition system to see a maximum of 5Kohms total ignition resistance, beyond that they state that damage to the ignition componentry will result.

I know of many Benz cars that are run on resistor plugs with no issues over extended periods. Some say poor idle results. I have found no evidence of this. Another urban myth maybe?

No one has been able to provide me with a cogent argument as to why a resistor plug should be problematic with the modern high energy discharge electronic ignition system.

mac911

Thanks Glyn!

When my plugs arrive (resistor Bosch), I'm going to take out 1 plug from each bank and double confirm what brand/model came in mine. Unless they happen to be R version of Bosch, I'm going to return them and wait a year, or get the Resistor version of NGK because the Resistor version of NGK is absolutely shown in owners manual, so I would feel comfortable with that despite resistor.

No resistor on Bosch, but resistor on NGK in owners book.

I'd prefer to play it safe like yourself and others, just use what's in there, or what's in the book. No need to take a chance on something else. Plus I need to change air filters anyway.

Thanks so much, confirmed my decision! Great information.

Glyn M Ruck

There is also no sensible reason why a Bosch resistor plug of the same heat range should be any different to an NGK resistor plug. Both brands make great plugs.

mac911

Both banks had Bosch with NO resistor. Therefore, I put off changing them.

I'll probably get the NGK with resistor that way I could always say "that plug is in the owners manual," if questioned for something. Or I might wait a year to even change them.

The Bosch with no resistor are too hard/expensive to get. With the right tools, changing plugs is very simple on these cars. Hardest part is honestly fussing the big air box on/off. I had first of two plugs out, 6 minutes after opening the hood. Thank goodness for longitudinal engines.

I am attaching picture of condition of old plug compared to a new (resistor) plug. You can see the shape of the plug, electrodes I guess they are called, are in very good shape (at least to my eye). Gap might be the slightest bit bigger, but I think they looked awfully good for 6 years and 45,000 miles. However, what do I know? Not much.

BTW, my threads looked/felt oily. I found another thread https://mbworld.org/forums/c-class-w...on-normal.html

Same oil looking substance. I guess the factory must put something on the threads.

Thanks to all for the help.

mac911

Ok...

All 6 plugs changed to NGK PLKR6A. Even though thats a resistor plug, it's in owners manual and many cars came from factory with that plug. Thus far, performance is fine.

I torqued at just 16 pound feet, when range is 15-22, hope that was ok, bit of a calculation error.

The other 5 plugs looked IDENTICAL to the used plug in the photo above.

Therefore, I think they were fine, but that is the entire point of maintenance. Don't let it get to the point of hindering the performance or putting stress on coil pack.

It was great to see how well the stock Bosch plugs held up though. With the right tools and past experience with air cover, it took exactly 60 minutes to complete. $69 for plugs. I can't imagine what I saved over the dealership.

redfox302

Excellent !!
My local shop is charging me $190 for labor and I provide them the parts.
I've been looking at types of spark plug for w204, Thank you for getting this done. Do you mind sharing with us what tools required for this job?

And yes, I read your post.
Thank you.

mac911

Sure. Of course you read it, no details there!

Take any words from me with a grain of salt though. I have virtually no car work background. Honestly, I must look stupid working on a car. Just reviewing my experience below, I'd consult professional videos or tutorials before doing any work.

By the way I bought plugs from Sparkplugs.com . Really good service. You find the PLKR7A more often than PLKR6A, but I wanted to use one of the plugs in the book (PLKR6A is one of those). They even send you (at least me) some free gloves to wear while working.

1) Remove both engine covers. Note how the main cover feels when fully seated over the air tubing at the rear of the engine.

2) You need a T30 bit to remove the coil packs. There are two T30 bolts on each coil pack. Also a driver only won't work because of the firewall on some of the back plugs. You really need a T30 socket on ratchet unless you have another T30 that can get into tight spaces and have leverage.

3) After getting the two T30 bolts off the coil pack, you just pull up and the coil pack boot pops off the plug.

4) Remove Plug. I used this cheap swivel spark plug socket on Amazon called : GearWrench 80546 . Actually not too cheap.

You need a small extension with that even though it's extended because of some of the spaces and you'll also bust open your hands if you try to do it without an additional extension (only an extra 1-2 inches needed).

So I used the plug socket on the ratchet (probably any 5/8-inch spark plug socket with proper extensions would have worked though). This one was nice as it even had a magnet to pull the plug out.

So I busted the plug loose, kept loosening by hand (takes a while), then pushed the socket down a little on the plug, and pulled each plug right out.

5) I stick new plug inside swivel socket and BY HAND, begin to screw it back into engine very slowly to not cross thread. Once it won't go anymore by hand, I put extension and torque wrench back onto socket and torque to spec.

6) Then I shoved coil pack and boot back down over plug and put T30 bolts back on. Move on to next.

7) I doubled checked that everything was tightened back, put engine covers back on. Made sure no tools were under hood. Closed hood, started car. Ran normal.

There is a video on Youtube. Search for M272 engine "M272 engine spark plug." The guy shows another engine too, but halfway through the video he gets to the M272 V6.

I do very little work on cars myself, but I simply know enough about these engines and watched enough videos, that I found it easy.

$190 labor seems a little silly since it's only 60 minutes, but if you're uncomfortable, you have to do what is best for you.

Honestly, for me, always the trickiest is hauling the main engine cover off/on because it's so big and awkward, and the intake hoses and a vacuum line get in the way.

You really have to get the back of the engine cover on perfect, where the air goes into the engine. If that isn't on there 100 percent, you can get codes and whatnot. That is the focus when installing the cover, to make sure it fully seats around the pipe in the back. I'd feel how it sits on there before you take it off, I know when it's fully on because I've had it on/off so many times.

Good luck. Based on how my plugs looked, I don't know how many miles you have, I wouldn't say it's the most urgent thing especially at my mileage. I just wanted to have it done for a few years.

romeo291

I have a 2009 C300 (Flex) and all the autopart sites I've checked said that I needed the PLKR7A plug instead of the PLKR6A plug? Is there a difference between the plugs in a 2009 model as opposed to a 2008 model?

raykar

I put the dollup of dielectric grease on the inside tip of the coil housing. Cleaner for the install that way. I also put some anti seize on the back third of threads of plugs. Don't put anti seize near threads at firing end as the firing end does protrude into piston chamber and you don't want any chemicals or debris coming off there. Good luck.

James Thedyanto

is there any performing enhancing spark plugs for w204, 2013?

Nicholi2007

Hi Mac,

I just mistakenly ordered YR7MPP33. It seems everyone online is selling resistor plugs unless you buy branded Mercedes. I did find them on Amazon although slightly higher (a few bucks more).

The manual states Y7 MPP33.

So following Glyn's logic just use them?

Nicholi2007

It's odd that your manual mentions NGK PLKR6A. That's a resistor plug. Basically anything with an R signifies that.

Bosch is no longer making the Y7MPP33 non-resistor plug.

My concern is that the alternator lifespan would be affected as you're putting in another layer of resistance.

I had an issue with the battery cable which has a sensor and was bad. Caused a major issue.

Call me paranoid, I just don't want to deal with any electrical gremlins down the road.

Amazon has them

superangrypenguin

Buy OEM through a wholesaler. It ends up at the same price.

Nicholi2007

Pulled the plugs at 113,000 miles. They were pretty brown. One looked like it rusted a bit and was tough to remove. My old plugs were Bosch platinum Y7MPP33. I replaced with double platinum YR7MPP33. Car runs fine as far as I can tell

Obviously the spark will be different but I presume performance won't be noticeable. My only concern is what affect it might have on the alternator over time.

Bigus-Dickus

I know this is an old thread but the extra resistance in the spark plug won't have any effect on the alternator. The spark is very high voltage (up to 20Kv) but very low current. The use of a resistor in the plug is to reduce electrical interference. As long as the resistor doesn't effect the performance of each coil pack, R type plugs should be OK to use.

Nicholi2007

Can you mix these plugs? I have 3 with no resistor and 3 with. I order 3 off ebay and it's the hand I'm dealt

Odd Piggy

If you must, yes, you can. The one without the resistor will cause some radio interference, especially on AM.