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Discussion Starter #1
Mine is a 01 E430. For a while it just sat in the garage but during the past 1.5 years, I have been driving it mostly on long trips. I'm now at 110k miles with OEM spark plugs and the only change in performance I see is a very slight drop in MPG - from 24 to about 22. So I'm wondering if I should just keep on going or replace plugs. Is it possible for the plugs to be fouled and not show a clear deterioration in vehicle performance? If I don't have to change them, I don't want to change them.
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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Mine is a 01 E430. For a while it just sat in the garage but during the past 1.5 years, I have been driving it mostly on long trips. I'm now at 110k miles with OEM spark plugs...
If you haven't changed them before, you are overdue! 100K or 5 years. If you DIY, then the cost isn't bad.
 

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E320/E250 Bluetec Ford F350 6.7l
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The 8% or so drop in mpg might be due to colder weather taking more fuel to warm up the engine or due to government putting more and more cheap stuff in our gasoline.
Still doesn't change the fact that plugs and O2 sensor are due at 100k
 

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Technically you don't need to change anything: plugs, sensors, fluids, etc., just ignore everything until something breaks. I can pretty much guarantee that is the more expensive route, though.

Fouling is not the issue. As the plugs arc to ignite the compressed fuel/air mixture, over time the gap increases and the plug's efficiency decreases. Newer technology extends the interval (raise your hand if you remember changing plugs once a year, as well as points and condenser), but it's not magic.

The plugs are done. Change them. But if you're not going to, then you may as well just ignore everything else, too. ;)
 

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2012 E350 :-) 2002 E320 (sold)
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FWIW, I changed the plugs on my 2002 E320 in about 2 hours for the cost of $48 for the 12 plugs. That was much better than taking the car to the dealer.
 

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Discussion Starter #7
Technically you don't need to change anything: plugs, sensors, fluids, etc., just ignore everything until something breaks. I can pretty much guarantee that is the more expensive route, though.

Fouling is not the issue. As the plugs arc to ignite the compressed fuel/air mixture, over time the gap increases and the plug's efficiency decreases. Newer technology extends the interval (raise your hand if you remember changing plugs once a year, as well as points and condenser), but it's not magic.

The plugs are done. Change them. But if you're not going to, then you may as well just ignore everything else, too. ;)
Stop being cynical and make an attempt to answer the question if you can. Here's the question again: If there's no sign of poor performance, do the plugs have to be replaced at the 100K interval? OR, when these plug go, is there any noticeable change in vehicle behavior? And yes, I will replace them, but this is info I'm curious about.
 

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2001 E320 - Brilliant Silver/Ash: 107,000+
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Slightly off topic but I don't like the fact that we can't get the exact OE plugs any longer. Are the Bosch replacements inferior, as good, or superior? All I know from reading is they are definitely different.
 

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88 560SL - 01 C240 - 02 W210 4matic Wagon - W212 4matic wagon
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I am also interested in hearing from those who have noticed any changes on the MB with just a plug change.

We have not noticed any difference on any of our cars -- even on our high mile fleet cars. And we keep detailed records -- so figuring out the MPG numbers is easy.

I was told by a Porsche engineer that concern over removal difficulties causes the five year limit - rather than any performance issues.

Always interesting hearing others opinions/ experiences
 

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99 E430, 01 E430 Sport, 00 SL500
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Gas mileage varies on how that car is driven, where in what season. It even depends on the brand of gas. If you just race once on the freeway, there will a noticeable drop in overall gas mileage. Sometimes, you think you top off the gas tank, you didn't. The pump fooled you. Some people think cleaning the MAF or new MAF can help gas mileage. I changed the plugs only when there was check engine light and it was misfire consistently on 1 or 2 cylinders. After plug, still misfire, it's the more expensive plug wires to change. More than 2 cylinders misfiring, it's something else. After the plug change, there should be no more code, no noticeable behavior in the engine.
 

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Stop being cynical and make an attempt to answer the question if you can. Here's the question again: If there's no sign of poor performance, do the plugs have to be replaced at the 100K interval? OR, when these plug go, is there any noticeable change in vehicle behavior? And yes, I will replace them, but this is info I'm curious about.
Again, FWIW, after I changed my plugs (2002 E320 96K miles), I noticed a smoother idle and more pick up when hitting the gas. Even better, my wife said the same thing before I mentioned it. I think plugs are like shocks in that they degrade so slowly over so many miles/years, that you don't notice it until you replace them.
I don't really check gas mileage.
 

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2000 E320
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IMHO, the plugs have been in that car for 10 years and over 100K. If, for no other reason, they should be pulled just to ensure they can be removed. So you may as well install new ones and be done with it. If you DIY, use compressed air to blow the debris out of the plug well, otherwise it will fall into the cylinder when you remove the old plug. Nice way to spend a sunny afternoon and save yourself some money. Make sure you have correct tools as you will probably need a "knuckle joint" on your ratchet to reach the plugs next to the firewall.
 

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Stop being cynical and make an attempt to answer the question if you can. Here's the question again: If there's no sign of poor performance, do the plugs have to be replaced at the 100K interval? OR, when these plug go, is there any noticeable change in vehicle behavior? And yes, I will replace them, but this is info I'm curious about.
Stop being cynical? I never agreed to that. :D

Seriously, though, I did answer your question in the second paragraph. Plugs wear out and it's a gradual process, just like fluids. If you actually wait until you *notice* a problem, you've gone long past a degredation in performance and economy.

If the analogy helps, think of cardiovascular disease. Blockage accumulates very gradually over a long time, and if not checked, Whammo, likely death.

Re: pulling plugs to check them, that made sense back when they were changed annually, particularly if you drove a performance car. But what is the benefit here? One, the platinum plugs are much harder to analyze, unless you're going to magnify them 20+ times you won't discern anything. (The casual owner won't understand what they're looking for anyway, much less someone who fails to reflect an understanding of why they are changed, and a pro's time is too valuable for such nonsense.) Plus they're relatively inexpensive and are good for another hundred K; just change them and you're good. If you develop a misfire you know it's not that and can look at something else. Otherwise you have to start with stuff that should have already been done and spend a lot of time suddenly you hadn't planned for. Not to mention if you develop problems away from home (Murphy's Law) you'll either face a towing charge or a nasty bill from a mechanic -- not to mention the inconvenience associated with it all.

I don't understand the waiting mentality here. At all. Is it cheapness? Laziness? Or just simple irrationality?


You don't like my cynicism; I don't like your whining. So stop being a whiner and tell me: what is the benefit of waiting?
 

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2001 E55 AMG
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If the analogy helps, think of cardiovascular disease. Blockage accumulates very gradually over a long time, and if not checked, Whammo, likely death.
What a happy chappy! I'll sleep better tonight knowing that my heart's about to pop due to my unhealthy lifestyle :thumbsup:
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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In other words a concientious owner WILL notice a change in performance - and since plugs now go out to 100K it's a affordable service element for the next 100K.

The original Bosch plug has been "imporved" and no need to go to a multi-electrode exotic

You can buy 16 plugs for around $90 delivered or $5.30 a plug (ebay) and the 17mm offset "tool" for like $30 (ohlord or ebay), making the total investment like $120. Add a can of diaelectric grease from a retail autoparts store for like $6, total like $126, like a hair over .126 of $.01 per mile... The tool is really worth it, don't conceptualize it, using it it's value becomes apparent. On V8's that drivers side rear most plug is still a bit of a pain.
 

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In other words a concientious owner WILL notice a change in performance - and since plugs now go out to 100K it's a affordable service element for the next 100K.
Not to put too fine a point on it, but even the most conscientious owner is unlikely to notice the degredation because it is soooo gradual. It's similar to shocks, where the ride deteriorates so subtly over such a long time it's never noticed, but then when new ones are fitted, the driver is like, WHOA, what a difference!

For the casual owner who is going to DIY, I continue to suggest that removing the lower engine mount bolt (one side at a time) and then raising the engine on that side makes a huge difference in working clearance since the engine pivots on the other mount and effectively increases clearance on the unbolted side. It adds perhaps fifteen minutes to the job, but the time and skinned knuckles it saves more than offset that bit of extra work. (Not to mention the reduced frustration.)
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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Just to answer the OP on the 'wear' on the plugs. I changed mine at about 105K on both my SLK320 and E320. In each case the plugs still looked visually good and the car performed well. BUT, the gap in each case increase by between 6 thousands and 8 thousands, Now that may sound very little, but percentage wise it was quite big.

I think if it was not for the dual plug system, the individual coils and the variable firing rate, one would probably have noticed a considerable decrease in performance.

That said, I did not really notice any difference in fuel consumption after changing the plugs.
 

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2002 E320 210.065
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I changed original plugs at 118,000 miles.
The old plugs looked suprisingly good, but the car had more solid acceleration in the middle range with the new plugs.

Your old plugs will probably keep sparking just fine until you are ready to do the job.

BTW, I installed the Bosch 4501 (IR Fusion+4; Iridium/Platinum with Four Electrodes). I bought them from Autohaus and after the rebate that was available at the time, they cost about the same as stock plugs. I've read here that our engines don't like them, although they have worked well in my car.
 
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