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- Fuel like smell from oil (dipstick, oil cap), so appears to be fuel dilution
- Same fuel like smell in garage when car has been parked hot. Goes away when engine cools.
- Rusty dipstick
- Oil cap test - when oil cap is resting loose it bobbles up and down.
- No other known issues. Drives great, no engine oil leaks
I’m going to take into a shop for diagnosis - but as I understand, the potential main culprits are:
- Valve cover (has integrated PCV)
- Some valve pipe below the intake manifold.
You pretty much described the symptoms of a plugged or malfunctioning PCV system. Fuel dilution can lead to early timing chain wear and to early camshaft adjuster failures. There are a number of components — check valves, lines, etc — associated with the normal operation side of the system that need to be checked before just diving in and replacing the valve cover. Your shop needs to have dedicated MB techs who are familiar with the M271.860 engine. The WOT side of the system is simpler and less expensive to replace if needed.
You pretty much described the symptoms of a plugged or malfunctioning PCV system. Fuel dilution can lead to early timing chain wear and to early camshaft adjuster failures. There are a number of components — check valves, lines, etc — associated with the normal operation side of the system that need to be checked before just diving in and replacing the valve cover. Your shop needs to have dedicated MB techs who are familiar with the M271.860 engine. The WOT side of the system is simpler and less expensive to replace if needed.
One minor point to clarify about the "oil cap test" - this was with the engine warm and at idle.
Yeah those exact concerns about timing chain wear and camshaft adjusters are why I change the oil at 5k miles max, sometime less. So I've got quite a concern here with fuel dilution destroying the purpose of the oil. I agree, I don't want to jump in and chase the valve cover. I want to get an idea of what could cause the issue, which I think you helped shed some light on.
Can you clarify what you mean by "WOT side of the system"? I assume WOT is wide-open-throttle, but I still don't get what you mean overall.
The part of the system you refer to as “Some valve pipe below the intake manifold” is referred to as the WOT system in the parts manual. I’m assuming this means wide open throttle, too. It’s got a check valve and maybe what is an accumulator in the line. I never had to service it on any of ours, but I suspect it only has a function under certain conditions of crankcase and manifold pressure. The parts don’t look expensive, but it’s difficult to get to.
The part of the system you refer to as “Some valve pipe below the intake manifold” is referred to as the WOT system in the parts manual. I’m assuming this means wide open throttle, too. It’s got a check valve and maybe what is an accumulator in the line. I never had to service it on any of ours, but I suspect it only has a function under certain conditions of crankcase and manifold pressure. The parts don’t look expensive, but it’s difficult to get to.
Awesome thanks.
I suspect the issue is somewhere here:
Last edited by WestonMerc; Jan 26, 2025 at 02:33 PM.
The parts don’t look expensive, but it’s difficult to get to.
The intake manifold has to be removed to access the valve. The check valve can be purchased as an assembly with all the associated hoses. One of those hoses is hard plastic, which tends to break when you remove the manifold.
Had a good Euro shop look at it. They believe its a leaky fuel injector, cylinder #4. Showed me the boroscope. It makes senses since I just had an oil change and the oil smells like fuel already.
The tech had recently come over from an MB dealer after 20 years and seemed to know his stuff.
Getting some quotes….
Last edited by WestonMerc; Jan 28, 2025 at 07:08 PM.
I must have misunderstood when they mentioned the intake manifold, I think he was referring to how the labor was broken out in looking at the previous quote I showed him. (This other quote was $1000 more in total) So the intake manifold did need to come out for the injector repair.
The damage came to $1100 for the main repair (replace one injector, replace all injector seals) plus an oil change. All genuine MB parts, even the oil. Not cheap, but not bad on labor at 2.5 hours @ $225/hr.
So far after bringing it into the garage at home, no fuel smell. Hopefully that does the trick, but I won’t call it a success until the oil has about 3-4k miles on it, and there is still no fuel smell outside the engine or from the oil itself.
But having a garage with poor ventilation has one advantage. I can smell when oil leaks/seepage when it starts to arise. For example I could smell when my Audi was starting to seep a little bit, which was coming from the upper timing cover. I could also smell a little something when the oil level sensor on the C250 was starting to get bad. But the fuel smell is definitely distinct and not a usual characteristic of the Audi or the Merc. I wouldnt say it smells like raw fuel, but definitely in the range of fuel-like.
Last edited by WestonMerc; Jan 29, 2025 at 09:48 PM.
I must have misunderstood when they mentioned the intake manifold, I think he was referring to how the labor was broken out in looking at the previous quote I showed him. (This other quote was $1000 more in total) So the intake manifold did need to come out for the injector repair.
The damage came to $1100 for the main repair (replace one injector, replace all injector seals) plus an oil change. All genuine MB parts, even the oil. Not cheap, but not bad on labor at 2.5 hours @ $225/hr.
So far after bringing it into the garage at home, no fuel smell. Hopefully that does the trick, but I won’t call it a success until the oil has about 3-4k miles on it, and there is still no fuel smell outside the engine or from the oil itself.
But having a garage with poor ventilation has one advantage. I can smell when oil leaks/seepage when it starts to arise. For example I could smell when my Audi was starting to seep a little bit, which was coming from the upper timing cover. I could also smell a little something when the oil level sensor on the C250 was starting to get bad. But the fuel smell is definitely distinct and not a usual characteristic of the Audi or the Merc. I wouldnt say it smells like raw fuel, but definitely in the range of fuel-like.
The 2.5 hours of labor seems very reasonable (the local MB rate for my area is "only" $195/hr). It took me over an hour alone just to remove the intake manifold. Good deal on finally resolving the problem.
I must have misunderstood when they mentioned the intake manifold, I think he was referring to how the labor was broken out in looking at the previous quote I showed him. (This other quote was $1000 more in total) So the intake manifold did need to come out for the injector repair.
The damage came to $1100 for the main repair (replace one injector, replace all injector seals) plus an oil change. All genuine MB parts, even the oil. Not cheap, but not bad on labor at 2.5 hours @ $225/hr.
So far after bringing it into the garage at home, no fuel smell. Hopefully that does the trick, but I won’t call it a success until the oil has about 3-4k miles on it, and there is still no fuel smell outside the engine or from the oil itself.
But having a garage with poor ventilation has one advantage. I can smell when oil leaks/seepage when it starts to arise. For example I could smell when my Audi was starting to seep a little bit, which was coming from the upper timing cover. I could also smell a little something when the oil level sensor on the C250 was starting to get bad. But the fuel smell is definitely distinct and not a usual characteristic of the Audi or the Merc. I wouldnt say it smells like raw fuel, but definitely in the range of fuel-like.
Jury is still out. It’s possible the issue is fixed. The fuel smell mostly seemed to arise after about 4k miles on the same oil, but now I’m doing 2k oil changes (about every six months) so wont really know unless I did an oil analysis.
The instance where I smelled the fuel right after an oil change (which led me change an injector) I do suspect if the oil was actually changed.
A bit more on this. When I open the oil cap, the cap does have a light fuel smell perhaps (this after about 300 miles since last oil change). So maybe not totally fixed. The dipstick didn't have a strong smell like before though. (The original dipstick was rusty, replaced is about 2,000 miles ago, looks normal right now.)
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