I have an 03 S55 w/ 40k miles. I purchased the vehicle a few months ago with 35k miles and it came with the vehicle service history. I had these services performed based upon the findings from the vehicle inspection and some as preventative maintenance. The following services were performed by a Mercedes shop:

Complete vehicle inspection
New fuel filter
New spark plugs
New valve cover gaskets
New oil and filter
Complete transmission service w/ new conductor plate, filter, connector, gasket, fluid
New ABC nitrogen chambers (1 was bad so I had all 4 replaced; when 1 goes bad, the others will not be too far behind)
New ABC filter
New ABC return line filter w/ magnet
New ABC fluid
New power steering filter and fluid
New front brake pads and rotors (brake fluid was flushed recently by previous owner)
New shifter (220-267-33-24)
New battery
New alarm horn

I noticed the MPG dropped by 1 to 1.5 MPG after the service was performed. I initially thought the drop in MPG was because of the change to the summer gas blend recently and/or because I also changed the wheels and tires to sticky Michelin Pilot Super Sport Tires - 285 30 20 in the rear and 255 35 20 in the front.

I checked the oil yesterday evening and noticed a very strong fuel smell in the oil. The oil looks dirty and appears to have a thin consistency. I have only put about 800 miles on the vehicle since the servicing.

I am concerned by the gas smell in the oil. I will be taking the vehicle back to the Mercedes shop that performed the services, but I cannot do so until late next week. This is my daily driver. I have to drive about 150 miles per day for the next 4 days. Will it hurt the vehicle driving it the next few days? Has anybody else experienced this with an S55? Is this common for an S55? I read through the previous S55 posts and did not see any mentions of this challenge.

I should mention that though I am mechanically inclined, a stroke has left my right hand with limited use. That said, is there anything I can check or do myself with my limitations that might help/diagnose/repair the challenge?

Thanks for your anticipated assistance.

 

Congratulations on the buy. Nice low miles car.

How does it feel when running? All 8 cylinders popping? No warnings?

If you don’t trust your nose, you can send an oil sample to a lab for analysis. Find out how much fuel contamination there could be in the oil. I use Blackstone labs. Request one of their kits online. Maybe your dealer or a cheaper Indy will help you get a sample. You can suck some out from the oil dipstick tube without having to get underneath the car.(lucky we have a dipstick in the ‘03s.)

Just guessing here...
Misfires? Unburnt fuel in a cylinder leaking down past the piston rings. Bad plugs (2 per piston)? Bad connection of the 2 plug wires from the igniter? Bad igniter? Broken igniter wires/connector? Could have been created during valve cover/spark plug services you purchased. There would likely be a misfire error for the offending cylinder. Scan it.

Are breather hoses reconnected on the valve covers?

Guessing that poorly seated intake valve/leaky injector can allow dribble of fuel leak down after engine shutoff until fuel pressure backs down. but that’s rare to have that combination of issues and only if you do very short trips where the fuel would not vaporize in a cold head.

Piston rings OK? Leaky rings can allow fuel to pass by into the crankcase.

 

After rereading your post I noticed you didn’t replace any fuel injectors. Did the dealer do anything to them? If they are leaking, they can deliver a lot of excess fuel that leaks down into the cylinder(s) walls.

So also check for leaky injectors/o-rings. Since you already spent a lot on (proper) maintenance, replacing injectors should be additional peace of mind to ensure you don’t burn out the engine.

If the dilution is really bad, get an oil change while waiting to see your dealer. You can do the suck out from the dipstick tube method. Any shop should have a suction pump to do this. You bring them a case of 0W40.

To answer yuur your original question, “No, this is not a common complaint.” Every car has a little oil fuel dilution, but not typically enough to notice in 800 miles.