Oil on plug
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Junior Member
Joined: Nov 2019
Posts: 41
Likes: 6
ML350
Oil on plug
I did a search and didnt find it, hopefully someone can help. I have a 2014 ML350 with about 221k on the clock. Luckily its always run great until now, the car runs rough and has a CE which is a misfire in cyl3. The plug in 3 looked pretty nasty compared to the rest but i went ahead and replaced all the plugs and all the coils (note to others, dont waste time removing the intake manifold to reach plug 6, it doesnt help!!). Initially the car ran flawlessly and after a couple days, the #3 cyl misfire came back. I went ahead and pulled the plug and see its covered in oil on the electrode. I was initially thinking valve cover gasket but not sure that would result in oil on the bottom of the plug... anyone have experience with this or an idea what the issue could be?
Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
M276 OILY PLUG
I did a search and didnt find it, hopefully someone can help. I have a 2014 ML350 with about 221k on the clock. Luckily its always run great until now, the car runs rough and has a CE which is a misfire in cyl3. The plug in 3 looked pretty nasty compared to the rest but i went ahead and replaced all the plugs and all the coils (note to others, dont waste time removing the intake manifold to reach plug 6, it doesnt help!!). Initially the car ran flawlessly and after a couple days, the #3 cyl misfire came back. I went ahead and pulled the plug and see its covered in oil on the electrode. I was initially thinking valve cover gasket but not sure that would result in oil on the bottom of the plug... anyone have experience with this or an idea what the issue could be?
Your local professional MB service center may need to further troubleshoot:
- Cyl compression test
- oil filter inspection for metals
- damaged cylinder components
- ECU coil MOSFET driver
- (before pin-pointing leaky injector!)
Last edited by CaliBenzDriver; Oct 14, 2025 at 07:40 PM.
Thread Starter
Junior Member
Joined: Nov 2019
Posts: 41
Likes: 6
ML350
You have 220k (Mi/Km ?) M276 with new plugs and coils that keep faulting No3: Bk1 rear cylinder misfire super oily and are wondering what to do?
Your local professional MB service center may need to further troubleshoot:
Your local professional MB service center may need to further troubleshoot:
- Cyl compression test
- oil filter inspection for metals
- damaged cylinder components
- ECU coil MOSFET driver
- (before pin-pointing leaky injector!)
Yep, 221k miles. I wasnt sure if it was something that could be fixed with a new gasket (valve cover, spark plug) or perhaps since its oil on the the electrode, its likely not those and instead something like worn ring or valve guide. Either case, if this isnt a typical issue that people have run into, i think im stuck taking to the dealer.
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Yep, 221k miles. I wasnt sure if it was something that could be fixed with a new gasket (valve cover, spark plug) or perhaps since its oil on the the electrode, its likely not those and instead something like worn ring or valve guide. Either case, if this isnt a typical issue that people have run into, i think im stuck taking to the dealer.
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
NO3 DAMAGED CYL
what should OP do to a low compression oily cylinder ?
Last edited by CaliBenzDriver; Oct 16, 2025 at 01:26 PM.
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From: Baltimore County, MD
'13 s212 63 p30. '06 LX470
Boroscope and determined if the cylinder wall is the cause. Oil would not be coming from the topside unless its a valve guide seal, which the scope could also help detect.
If its not a wall or the valve, its likely the ring.
Can also quickly check for blow by by seeing if the oil filler cap dances.
IME, a berrymans soak of the piston overnight while occasionally rotating the crank will get that ring unstuck pretty quick if that is the problem.
Op, if it's a valve cover gasket, you will see a leak around the edge of the gasket. What I do not know if there are any sparkplug tube seals in that engine, which could leak, but in these cases, oil would be from the top of the plug and not on the electrode.
End the process with some restore and protect...
If its not a wall or the valve, its likely the ring.
Can also quickly check for blow by by seeing if the oil filler cap dances.
IME, a berrymans soak of the piston overnight while occasionally rotating the crank will get that ring unstuck pretty quick if that is the problem.
Op, if it's a valve cover gasket, you will see a leak around the edge of the gasket. What I do not know if there are any sparkplug tube seals in that engine, which could leak, but in these cases, oil would be from the top of the plug and not on the electrode.
End the process with some restore and protect...
Last edited by Baltistyle; Oct 16, 2025 at 07:58 PM.
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With that amount of miles, it’s probably a leaky valve and he’ll need to remove that head. It also could be a cracked piston ring.
A leak down compression test will need to be done to determine that. This is more involved and requires pressurized air being put into the spark plug hole and listening where the air is leaking from. The cylinder being tested will need to be at TDC. If the exhaust valve is leaking, the air will come out the exhaust. Intake valve, the air will come out of the air intake. Piston rings, the air will come out of the oil filler hole.
With 221K miles, it would be smart to rebuild the top end, not just #3 cylinder.
A leak down compression test will need to be done to determine that. This is more involved and requires pressurized air being put into the spark plug hole and listening where the air is leaking from. The cylinder being tested will need to be at TDC. If the exhaust valve is leaking, the air will come out the exhaust. Intake valve, the air will come out of the air intake. Piston rings, the air will come out of the oil filler hole.
With 221K miles, it would be smart to rebuild the top end, not just #3 cylinder.
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Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
SELECTING DEALER SERVICES....
I wonder if it would be best to drive this gently used 221.9k.Mi vehicle to the sales trade-in instead of the service advisor lane ??
Cost of immediate repairs will be upside down above residual value.
Tranny repairs will trail engine condition.... this vehicle is unlikely to see 300k.Mi
Cost of immediate repairs will be upside down above residual value.
Tranny repairs will trail engine condition.... this vehicle is unlikely to see 300k.Mi
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Thread Starter
Junior Member
Joined: Nov 2019
Posts: 41
Likes: 6
ML350
Thanks all.
As CaliBenzDriver said, if the head has to come off, I cant justify the cost of this for a car with this many miles as Im sure more will go wrong with it.
Ive done compression tests on my other cars but not on this one. I assume its a matter of killing the fuel pump or injectors and pulling all the plugs and then turning the engine over with the tester installed. Even if i find low compression, i still wont know whats going and dont have a way to do a cylinder leak down test. I hate to do it but i guess I can take to the dealer and pay the $250 to confirm the issue and be prepared to eat that cost. Wishful thinking but i was hoping it was a problem others ran into and not a huge job.
As CaliBenzDriver said, if the head has to come off, I cant justify the cost of this for a car with this many miles as Im sure more will go wrong with it.
Ive done compression tests on my other cars but not on this one. I assume its a matter of killing the fuel pump or injectors and pulling all the plugs and then turning the engine over with the tester installed. Even if i find low compression, i still wont know whats going and dont have a way to do a cylinder leak down test. I hate to do it but i guess I can take to the dealer and pay the $250 to confirm the issue and be prepared to eat that cost. Wishful thinking but i was hoping it was a problem others ran into and not a huge job.
