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Rust inside cylinder head spark plug threads. Should I do anything or be concerned?
So I'm changing my spark plugs for my 100k service on my 2017 E43. There is some rust inside the socket where the spark plugs screw in. Should I be concerned?
Also, should I spray some WD-40 or something in the threads? Is that advisable? The spark plug came out pretty easily but I'm still wondering if I could put something on there. I have no idea how that would be properly cleaned out..
So I'm changing my spark plugs for my 100k service on my 2017 E43. There is some rust inside the socket where the spark plugs screw in. Should I be concerned?
Also, should I spray some WD-40 or something in the threads? Is that advisable? The spark plug came out pretty easily but I'm still wondering if I could put something on there. I have no idea how that would be properly cleaned out..
Note that I haven't checked the other five yet...
some moisture got in there - engine pressure wash? Somewhere in the lifespan
How long do you plan to keep it? If a long time then plug that home with the plug and spray some wd and brush that out - nothing can get into the cylinder as you know
I've seen people find similar bolts that thread like spark plugs to block the hole to clean out the well - this deletes the obstruction of a plug in the well while you're cleaning with a rotary tool and a long brush attachment
don't add anything like wd to the plug threads - just dielectric grease to the boot as usual and anti seize to the plug threads if you want - your plug threads look rust free - this is not a big issue but would just survey to see where the moisture may have come from since it's one cylinder only
your well has traces of rust as well - this car saw moisture at some point that drained down there to gravity into the well and pooled at that spot
Last edited by PeterUbers; Oct 18, 2025 at 11:12 AM.
I think I plan on keeping the car at least another couple years. My wife says if I get another daily, she wants it. So it could be in the fleet awhile.
I've never power washed the engine but I can't speak for previous owners.
I'm nervous about messing around down there. It looks like there is some rust that could be sucked out but I don't have anything small enough to get in there. After I get the spark plugs torqued, maybe I'll at least try sucking the rust with a vacuum and then use a wire brush. Unfortunately, I'm not set up right now to plug the hole with a bolt and clean everything with a rotary tool. Maybe I will come back in later time and do that.
I'm not really an expert, so I'm not sure if the spark plugs show normal or excessive wear. They definitely look rusted to me.
Every single spark plug well looks like it has rust in it. I used a boriscope to take pictures of all six. Here are the pictures in order from passenger front to rear, then driver front to rear.
Oh, just to confirm, the spark plugs are torqued to 23 Nm needed meters and the coil packs are torque to 9 NM, correct?
Definitely looks like rust now that I look at the plug hole in your first pic. Moisture is getting there somehow or has in the past HOWEVER:
keep in mind the head of the e43 is aluminum I think - that doesn't turn brown when aluminum oxide sets in.
the discoloration of the plugs may not be rust or all rust - could just be burned oil or additives (file additives are colorful and coat everything) but likely just oil deposits. Rest of those holes look good
**are we even certain this is rust??
BIG PICTURE- you're fine and the car is fine and you'll enjoy this car for 2 years but this rust won't be a reason you get rid of the car or have issues with it
if a car sits a lot outside it can develop moisture that falls to gravity
how did the boots look? Plugs otherwise seem like normal wear - how many miles on them?
i don't know exact torque numbers I would also have to google those
Last edited by PeterUbers; Oct 18, 2025 at 03:52 PM.
1 second his point; the heads are made of aluminum so they don't turn red. When changing spark plugs you should blow out the hole after removing the coil, but before you remove the plug. That shoudl blow out any rust or debris that fel into the area. Still...that does't explain why there's rust in your spark plug well in the first place.
1 second his point; the heads are made of aluminum so they don't turn red. When changing spark plugs you should blow out the hole after removing the coil, but before you remove the plug. That shoudl blow out any rust or debris that fel into the area. Still...that does't explain why there's rust in your spark plug well in the first place.
Great question. And where would burend oil come from on the outside of the spark plug??? Normally burned oil forms a gooey film that would stick to the aluminum, not little fleck like in the picture. I guess if dirt was mixed with oily it "could" form little pellets like that. Main thing is what you said earlier, probably nothing to worry about.
if a car sits a lot outside it can develop moisture that falls to gravoty
how did the boots look? Plugs otherwise seem like normal wear - how many miles on them?
i don't know exact torque numbers I would also have to google those
I'm not sure about its previous life, but I always garage the car. But of course, it's still sits outside when I'm at work and we had a pretty rainy season.
The plugs looked okay to me. I didn't see any cracking or any foreign substances inside of them. I believe the plugs were changed at 50,000 mi, so these ones had 50,000 mi on them. I would have to double check my service records but the previous owners were on top of routine maintenance.
I'm pretty sure those were the torque numbers. I compared them from a couple different sources. They are what I used and the car seems to be running great now, better than before the service. My idle was actually starting to get a bit uneven. Now my idle is pretty smooth. No codes either.
The car also said I was averaging 25 MPG, on the way home yesterday, which I have never seen happen on that trip. It will be interesting to see if I actually receive a fuel economy improvement. I track my MPG every tank so we shall see.
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