Hey,
I changed my plugs and wires today, to everyone's favorite (IK20 and Magnecor).
Not too hard of a job, but I was brought to tears by the fact that every old plug I removed had oil on it. Not a large amount of oil, but enough that I could tell it was oil.

Engine has 26000 miles on it, runs strong, and doesn't smoke or lose oil.
Do you think this is a consequence of changing the plugs in a car that has just sat for 36 hours and maybe has a little dribble through the valve guide seals?

opinions?
regards,
Pete

 

You made an excellent choice for the plugs. The wires will not be better than stock, but won't do any harm either. The plugs on a 26,000 mile engine run on premium gas in the US should be a toasty brown, like a properly done marshmello. The gap may be slightly wider than spec, but no more than .01mm over. Oil should not be present, even if the car sat for months. I would haul out the borescope and look in the sparkplug hole. If only one plug was oily, I would suspect a valve seal or guide, or a ring problem with a specific piston. You indicate that all plugs seemed oily.

I would look at pressure inside the crankcase. Excessive pressure in there can cause oil to be forced down the valve guides, or up through the gap of the the oil scraper ring. Sometimes this can occur when there is a defect in the plumbing between the crankcase and the intake. Just a guess on my part, but it might pay to let a pro have a couple of hours to diagnose.

 

Thank you very much for the info. I got the car in December from a CarMax and when I drove it home, the oil overfill light went on. I drove it lightly and took it back the next day for them to drain and refill the engine. It has never since come on. Other than that I have never seen any alarms that would indicate high crankcase pressure.
This sounds quite scary.

Regards,
Pete

 

Did you run the car up to temp the last time it was used before changing the plugs? If it had only been run for a few mins and then shut down, I would not be too worried about a trace of oil.

As you say the car does not smoke, and uses no oil, I would run the car for a few thousand miles and pull the plugs again for another inspection.

 

No I didn't. I started it up for like 2 minutes to pull it into the garage.
For what it is worth, the service advisor at the Benz dealer didn't think it really needed looking in to.

Regards,
Pete

 

I agree with your Benz advisor. Pistons don't swell and seal up fully until engine has warmed. I think you can sleep soundly tonite!!

 

Hey man ... just thought you should know...

i bought a 2002 audi s4 from carmax and the next day i sent it to Audi for dianostic hence the 5 day return policy i was making sure i got my monies worth... though come to find out i need an entire front end suspension replaced... or so at least Audi said so .. and well i drive the car back to carmax and show them the default on the workmanship and the possible life threatening problems all the tie rod bushings and connections were nearly blown out... they could have poped out at any time...

so i would take your benz to mercedes and pretend something is wrong so the diagnosis can be covered under warrenty or pay for a vehicle inspetion for a couple hundred... my worry is there is somthing else wrong with your car...

good luck

 

When I pulled my plugs at 35,000 miles, half of them had oil on thread. I worried a bit, but figured it was just probably because I like to run my oil to just about max on the dipstick. My oil pressure is a bit high, but not out of spec. At this point, I'm not really worrying as my car runs fine, but let me know if you have anything.

 

New information is helpful. First, modern Mercedes engines don't swell to seal anything. The pistons, rings, and cylinders are designed and machined in such a way that the seal between cylinder wall and the rings prevents oil from entering the combustion process. This is a requirement, so that you don't have excessive polution and pack in the Cat before the warranty is up. AMG engines are hand built and have a closer to blueprint "fit" than standard assembly line motors. This makes them less likely to allow excess oil into the combustion chamber.

What can cause the oily plugs is overfilling the crankcase with oil. That is a real problem that can cause significant damage. Oil can splash onto the cylinder walls and work its way into the combustion chamber. This might be where your oil came from.

If CarMax changed the oil, and over filled it, they might not have installed the proper synthetic oil. Check your manual to see what specification sheet is for your car. Just guessing it is 229.3. You should, however, be using 229.5 oil (Mobil 1 0W 40 in the USA) with a fleece filter. Make sure it says spec 229.5 on the bottle.

The fleece filter has been specified since Sept. 1, 2003. It is part number 000 180 26 09. This replaced part number 000 180 23 09 and 000 180 22 09. This fleece filter when used with sheet 229.5 oil allows the extended service interval of 1 year/ 13000 miles. The oil and filter are for engines 112, 113, and 137. If you are lucky enough to have a 112.960/961 or 113.990/991/991 engine (The AMG engines), the change interval remains the same as specified in your manual, even with the fleece filter.

The filter 'kit' from Mercedes comes with a Mann HU 718/5 filter, also marked with a star and A112 184 05 25, and four O rings to reseal the housing. The filter has brown colored ends and white pleated filter material. The entire cylinder is wrapped with string saturated in glue.

Make sure you have the specified oil, and the right filter.

 

Thank you for all the excellent information.
Needless to say, I don't take this car to CarMax for service and never had planned to. I thought they should foot the bill for the synthetic oil since they overfilled it in the first place. They stated they used Mobil1 when they drained and refilled the oil to fix the problem with the overfill light, but it is probably worthwhile to do it again myself to make sure it was done right.

Regards,
Pete