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I'm about to do Spark Plug change on a 2011 E550 Cabriolet. (92k Miles - no idea if they have ever been replaced before)
I took one out to check what sort it was so I could replace it with the same thing
3 questions for anyone happy to reply
1 - Does this look like it needs to be replaced?
2 - There was a bunch of gunk on the thread, I assume that this is anti-seize material. I though the Bosch plugs should be installed without any of that
3 - Is there cause for concern about the oil on the thread? (I didn't check any of the others to see if they were the same). The plug well was completely dry
No idea on questions 1 or 2. But I replaced the spark plugs when I bought my 550 at 19K miles or so (car was 13 years old at the time). My plugs also had some oil on the threads. I though it was odd, but I don't think there's anything wrong with my car, so I would have to assume it's somewhat normal. I don't think the valve cover seals are known to leak, so I don't think that's a source (at least on most cars).
Two years later, my car now has 33K+ miles on it and seems to be fine (and no issues noted by my mechanic), so there's that.
Looks well used to me and i would replace especially since you dont know when or if they were ever replaced. I believe they should have been replaced at 80,000 miles/8yrs, did you have the car when it hit 80,000 miles?
I would not use any type of anti-seize on the threads. Bosch touts nickel plated threads for anti seize and corrosion protection.
With the threads looking a little oily I would inspect your pcv system. What engine is that, M273? Should be a breather cover on the drivers head, then a breather cover on the back of the passenger head. Pull the hoses leading to the throttle body and check for oil.
The cover on the drivers side can be cleaned if needed, theres no moving parts to wear out unless the gasket is leaking. The gasket is pretty durable unlike the gasket on the passenger side cover so I had no problem reinstalling it.
Imo the most important part is the insulation around the electrode. That one is not too bad, but certainly not good. I would replace because it's only downhill from there. The oil has nothing to do with the plug. The gunk I dunno, maybe zinc anti-seize?
I use anti-seize, especially on Alum heads. Ideally the copper flavor. A guy at work last week asked me what I thought about a plug he just busted off in an alum head. All the plugs but one came out normally, but that one wouldn't budge and ultimately the nut broke off. He might get lucky and get it with an easy out, but I doubt it. In that case the head has to come off. F that, use anti-seize.
The reason some say not to use anti-seize is heat transfer, less of it with anti-seize, but I do not believe it and have had zero issues with a variety of engines.
I'd also suggest you blow out the cavity the plug is in because they tend to collect sand dirt and nasties. I've even seen small rocks in there. Then when you remove or install plugs it can easily get in the cyl. I usually use an air gun with a nozzle that can reach all the way in there to break off the junk. If needed I'll use Carb cleaner or water to get stubborn stuff out, then again a final air blast.
Plugs are one of those things you trust nobody with. I tell people; do you really think the guy making $20/hr is going to clean, or just remove and slap a new plug in? Often you need a swivel socket so the plug tip drags along the bottom, collecting any debris and shoveling it right in the cyl. Most people don't even look to see if there's crap in there, so they're just as guilty.
Note what plug comes outta what hole so you can note which had bad plugs, if any. For example you might have an oily hole where you need to swap that one plug more often. Or maybe a clue your PCV is sucking oil, which usually shows up with the closest plug to the PCV being oil damaged. Or maybe a lean condition cluing you to a clogged injector, etc etc.
I've been looking at a lot of videos and you are right, there can be a lot of crap in the wells. It didn't even occur to me to clean them out before removing the plugs.
I was going to replace the plugs in my M272 engine just never got around to it. carfax shows they have been replaced at the appropriate mileage intervals so not too concerned. Engine has over 160,000 miles and runs great.
I did go thru the pcv system. I replaced the passenger side breather cover and drip pan. The old drip pan looked really good, no wear on it so probably didnt even need to replace it. I even sold the old one on ebay for a few bucks. There was a small amount of oil in the breather hose going into the elbow at the maf sensor housing. I cleaned every and put it back. Replaced the breather cover because the gasket is so soft it flattens and it really is one time use deal. Cleaned the throttle body while in there.
Breather cover on the drivers side I just removed and cleaned it then reinstalled. I did buy a new cover but realized there is nothing inside it to wear or fail. The gasket on those are seem pretty durable so reinstalled and have no issue with leaks.
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