Oil smells of petrol?

[AdamG]

Hi,

I'm a little concerned by my e240's oil which smells strongly of petrol. I'm not sure what would cause this? The coolant is clear with no gunge and there seems to be no imulsion on the oil cap.

I'm not sure if this is signifiacant but after a short journey the fuel filler cap hisses when opened.

I'm sure it is a bit down on power and a couple of times (if floored) it seemed to go to limp mode where not all cylinders were firing. No light came on and if stopped and restarted it would be fine?

Thanks

Adam

 

[Dieselman]

The fuel cap hissing is normal (I think) as the system becomes pressureised to aid the fuel flow.
The fuel in the engine oil is due to the incomplete combustion causing fuel to wash down the bores and into the oil.
Firstly fix the misfiring problem then change the oil for a cheap oil and drive it pretty hard for a few thousand miles. This will remove the glazing that has probably built up on the cylinder walls.
Then drain and refil with good oil again.

Don't leave this problem as the diluted oil has less wear protection than oil on it's own.

The 240 V6 has a tendency to glase the bores so may be suffering low compression and high oil consumption as a result.

 

[AdamG]

Many thanks for the advice. The engine runs dead smooth and I have recently changed the MAF with a pierburg as shown in the "how to"
Also I have fitted new plugs and leads as there was a slight miss on idle.

The misfire only occurs if it is driven very hard.

I will change the oil out right away as it has been about 20K with the service indicator nearly up.

What viscocity oil do you recomend 15W/40 semi-synth.?


Thanks again

Adam

 

[Dieselman]

For now I would use a mineral oil to help bed the rings better, then I'd go back to full synth, especially if you intend to leave it for 20k between changes.

 

[Karl]

Surely 20,000 miles between oil changes is far too long, even if using synthetic oil.
Maybe better to use a mineral oil and change it at 5000 mile intervals?
Even at 5000 miles the oil will be dirty.

 

[AdamG]

Thinking about it, it does seem ridiculous 20k intervals. The service interval on my landrover is 6000 for the oil.

The service indicator never seems to go down proportionally to the milage. For example it will only reduce by 100 miles but I may have covered 200 miles or more.

 

[Parrot of Doom]

I would never use mineral oil on a permanent basis, frankly its rubbish compared to fully synthetic.

20,000 miles is probably about the limit, but I've run mine for 13,000 miles on the same oil. If you're running to 20,000 miles, I'd consider changing the filter at half that. I don't think you'll do any damage.

 

[Dieselman]

I would never use mineral oil on a permanent basis, frankly its rubbish compared to fully synthetic..

The mineral oil is just to bed the rings.. Bore glazing is a result of oil passing the rings due to lack of compression, the oil then bakes onto the bores making the problem worse. A higher quality oil can exaccerbate this problem hence use a low quality oil to allow the rings to cut through the glaze (if they can) then revert back to a higher quality oil
The harder driving style will create greater compression pressure and heat which will help.

20,000 miles is probably about the limit, but I've run mine for 13,000 miles on the same oil. If you're running to 20,000 miles, I'd consider changing the filter at half that. I don't think you'll do any damage.

The best thing to do is to fit a bypass filter. You need never change the oil again but the engine bays are a bit tight.

 

[AdamG]

I've put the mineral oil and new filter in and am going to drive it hard. I will let you know how I get on.

The oil that came out was filthy black and stunk of petrol...was definitely worth doing. I like the way mercedes put the filter on the top of the engine this makes life a lot easier.

Thanks again

Adam