[KTMJay]

Ok 1st I’m curious, but have racing experience and want to ask this question about spark plugs. I have gone so far as to index my spark plugs in my supercharged 89 saleen, true I cannot tell the difference in power but know you don’t want a flame out and my spark plugs are gaped closer for that reason.
Now a Mercedes Benz recommends service life of spark plugs at 100,000 miles, but most double platinum or iridium plugs recommended replacement at 100,000 km or 62,000 miles, that is what the manufacture of plugs says on average.
The average normal wear or gap growth is around 0.10-0.15 for every 10,000km or 6000 miles, double platinum and iridium’s wear slightly less and the wire will lose its flat edge,start rounding{if my math is correct on this???} around 0.48 to 0.73 every 48,000 miles. Now at 62,000 miles gap increase is around 0.62 to 0.93 So if our gap starts at .40 it’s going to be .46 to .49 gap at 62,000 miles, that means your gap is now approaching maximum gap, to me [.50 is max]10thousand over. now going 100,000 miles means your gap is going to be around .58 which was where some of mine were, .60 most were and some were above .63.[Plugs changed at 104,500 miles]
Knowing this your ignition and your coils are working harder as your gap increases putting more stress on your electrical system. Coils cost around the same price as 12 or 16 spark plugs if you buy your plug locally. Wouldn’t it be smarter to use the advice of the spark plug manufactures as we know MB’s not always correct?
Ok we have a 3 valves and 2 spark plugs per cylinder, knowing that the intake plug is the most important plug in the system, exhaust is not as important. In my rice burner we changed the intake plugs every 10,000 and both at 30,000 was a race car. With that in mine I was thinking why not change intake spark plugs every 50,000 miles, clean an re-gap your old plugs and put them in when you change your plugs again at 100,000 in the exhaust side.
Personally will change or check plugs at 50k just to see what gap I have. Yes, maybe I thinking to performance oriented but gas mileage and performance will be better by doing this.You will have less stress on your ignition system. Am I correct on this or am I just blowing hot air, don’t beat me up to much,I just wanted you smart people here think of my thoughts.

 

[johnma]

too much math, I just want to get it done and get back on the road.
JM

 

[pte]

spark plug life. get your facts straight., On M-112 & 113 engine

Here is some helpful info , Because the ML has a high gear ratio ( 3.70 to 1 ) your engine is turning more revolutions per mile , meaning more sparks ? ignition hits to the spark plugs per mile . The plug location & Ignition coils are labeled A & B. They are staggered spark . (A) s/p is fired 1st , then several Mili seconds later (B) s/p is fired. These spark plugs have protruded tips. they are in the combustion chamber pretty far , So Indexing them will not help. They are right in front of each intake valve. See the picture below. The staggered spark is for emissions. The S/P are not designated as , (1) for intake & (1) for exhaust . There is a coolant path between each S/P and the exhaust port to help dissipate heat that travels through the S/P. Heat range is important. A Colder plug has no life . My ML With OE iridium spark Plugs &3.70 gear ratio , at 68, 000 miles had a .060 gap and the center electrode was badly worn & had a rounded tip.. I installed Champion dual platinum , a 1/2 heat range hotter all is well I've Had great luck with Champion spark plugs , been using them since 1969 , You just had to get the heat range correct . Cross reference is not always right. Here is some more good reading
http://www.marcusfitzhugh.com/CLK/W208-3.html

Cheers _PTEngineering

 

[megadamp]

pte. I installed Bosch FR8DPP33+ spark plugs, bosch number 0242230500 but they are +45. Any idea what the +45 means.

 

[KTMJay]

to megadamp;good question, the + is for super plus, the 45 is what they refer to short code and be damn if i could find out what that meant,other than it is super ceded by Bosch to part no. FR8DPP33+ now super+45
pte sorry should of said used to index plugs, not on the ml. thank you for the picture that really helps seeing that the position of the plugs to the valves. Makes me wonder why we changed the plugs the way we did, just because every body else did, and No we didn't jump off a bridge if every body else did
seams like you are also on the same thought wave as me on changing plugs more often.you have to check them in order to know if they need replacing and 100,000 miles is a long time. i am going to look up that other reading you posted thanks again

 

[BernardFarquart]

I changed the spark plugs in my E320 at 80K miles, just because I couldn't get my head around going 100k on a set. I was surprised to find very little gap erosion, and only a bit of normal brown deposits on the plug.

I removed the original plugs, and elected to replace them with NGK laser iridium, but I easily could have waited the 20k longer.

 

[megadamp]

My old original Bosch platin R1963 were changed around 107k and were approx 15% worn/larger gap at 1.15mm. Thanks KTMJay for the info.

 

[megadamp]

Oh and the electrode on the new plugs were pointed (sharp point) rather than the flat ones on plugs i have seen.

 

[cmitch]

I ran a set in my ML430 well over 100k. I think I had 155k+ on them when I pulled them. They didn't look that bad, either. I think fuel quality has a lot to do with plug life.

 

[KTMJay]

good gas is always good, but one of my points is when your gap increases its do to the spark of your coils wearing down and rounding your electrode tip. The gap being the important factor in this, as it puts more load on the coils,meaning they have to increase there output,which will were down your coils. replacing coils at 90 bucks a piece; or 55 bucks, for me only 12 plugs. changing them at the 60,000 or + miles keeps your electrical components working at there peak.
megadamp, im glad to return a helpful post to you as you have done many for me, a sharp point, like a dart tip. never seen that before

 

[megadamp]

good gas is always good, but one of my points is when your gap increases its do to the spark of your coils wearing down and rounding your electrode tip. The gap being the important factor in this, as it puts more load on the coils,meaning they have to increase there output,which will were down your coils. replacing coils at 90 bucks a piece; or 55 bucks, for me only 12 plugs. changing them at the 60,000 or + miles keeps your electrical components working at there peak.
megadamp, im glad to return a helpful post to you as you have done many for me, a sharp point, like a dart tip. never seen that before

KTMJay. Thanks for the kind words. Thats the way i like it. We all help each other out on here. Well sometimes ha. The longer you hang out the more you will understand.
Oh and yes like a dart tip, found that strange as i would think as the tip wears down it will alter the spark?.

 

[43sqd]

good gas is always good, but one of my points is when your gap increases its do to the spark of your coils wearing down and rounding your electrode tip. The gap being the important factor in this, as it puts more load on the coils,meaning they have to increase there output,which will were down your coils. replacing coils at 90 bucks a piece; or 55 bucks, for me only 12 plugs. changing them at the 60,000 or + miles keeps your electrical components working at there peak.
megadamp, im glad to return a helpful post to you as you have done many for me, a sharp point, like a dart tip. never seen that before

You've "never seen that before" because you are using the old style spark plugs which never came as standard equipment in an ML. The OE plug has a laser tip central electrode (dart tip).

It's obvious that if you bought your ML used, it either had the wrong plugs in it and you changed them with the same number or you chose to change the newer style plug with the old style.

The laser tip spark plugs are coated with platinum or iridium or a combination of both, one or the other on the central electrode and the other on the ground electrode.

These precious metals prevent wear of the electrodes to a very minimal or negligible standard which requires less maintenance And the laser tip is used to intensify the spark providing a complete burn.

Ignition coils are programmed by the ECM to fire at a certain time and with a specified amount of voltage. It will do this every single time it fires and will not change those specifications if one or all of the spark plugs have a larger or smaller gap. The ECM has no idea what condition the spark plugs are in, neither does the coil/s. Coils do not have to work harder because of a larger or smaller gap and does not cause the coil/s to wear out or damage it as a result.

So, suggesting that everyone change their spark plugs every 60K miles is a waste of time and money. They are rated for 100K miles and well beyond that.

 

[TimsML430]

I would concur, replaced 16 with BOSCH FR8DPP33+ at 267,445 KMS. I have owned the ML since 2005 and believe the plugs have never been replaced (at least since I have owned ) Purchased with 81,000 KMS, so there you go.

 

[KTMJay]

thank you 43sqd ,sorry for the wrong visual thought of a dart tip,which is pointed on the tip. Your second picture shows a very narrow tip {new style},but that tip is also flat at the tip,sharp on the edges.It would not pass in England for a dart tip
Yes, i bought it used and the plugs were the old style, but BM sold it new, with double platinum Bosch plug.
the info on the wear of the plug i posted was from NGK and Denso that is on there new laser tip and that is what most of the info out there says.I do believe they should last at least 80,000 miles, but when my plugs are at 50,000i will check them
Now as for the info on the electrical output, that came from Bosch,now im not savy on mercs,I do know on mustangs and vets the computer knows that the spark plug needs more voltage, and will increase it accordingly., just like if on a vet you have bad gas or your engine is to hot,summer time, it would retard the timing.Your right that the ECM doesn't know your plugs are wider but it does know that it needs more input and adjust to the condition's or am i way off base on this