Please help: I have a 1992 MBZ 300CE with 152K miles. I noticed that the engine started idling rough after a brief trip at highway speeds (75-80 mph), so I pulled the spark plug wires for inspection. To my horror, I found the spark plug tube for the #2 cylinder about one-third filled with fresh engine oil (by "fresh oil", I mean that it wasn't dirty or caked - so it looks like the oil has only started to collect recently).

I blew-out the oil using compressed air and paper towels - cleaning the tube as best I could. I visually inspected the valve cover gasket and as best I can tell, it doesn't look like the oil is leaking down into the tube from the valve cover gasket.

With the #2 plug wire removed, I started the engine. Looking down into the spark plug tube, it appears that a small amount of oil is bubbling from around the spark plug threads (between the head and the spark plug). Regardless of where the oil is coming from (either down from the valve cover or up from the cylinder), is it normal for gasses to escape out through the threads between the head and a spark plug?

I visually inspected the engine oil and coolant and don't see any sign of co-mixing and I don't see anything abnormal in the exhaust (no white or blue smoke). I am not a mechanic and opted not to pull the spark plug from the head (I have an appointment with a mechanic for later this week). I am, however, very curious and terrified as to what is going-on.

Could it be a blown head gasket? Could it be a cracked head? Could it be a defective piston ring or a terribly worn valve guide? Any idea as to the most likely cause before I take the car in?

The car has not been overheated. Usually, the car runs excellent and the only anomoly I can think of is - once in a blue moon - after the car has been sitting for a day-or-so, I will get a noticable, single "poof" of white smoke from the tailpipe when the car is first started. Other than that, the exhaust appears normal. PLEASE HELP!

You just need a new valve cover gasket which will come with 6 donuts rings for around the spark plugs - no big deal, a fairly easy DIY project.

You state that it was filled with fresh engine oil. Could someone have spilled some oil when they were adding oil to the engine?

Scott P.

The car had an oil change about two weeks ago at a reputable shop; however, it would have been virtually impossible for someone to pour oil in the spark plug tube because the plastic cowling atop the valve cover was installed at the time. By "FRESH OIL" I was trying to illustrate that this problem seems to have started quite recently - the oil was not dirty or "caked" inside the spark plug tube. It looked pretty fresh.

"With the #2 plug wire removed, I started the engine. Looking down into the spark plug tube, it appears that a small amount of oil is bubbling from around the spark plug threads (between the head and the spark plug). "

Have you tried tighten the spark plug?

Bowin: I have not attempted to tighten the spark plug; as I don't have a torque tool and I don't have a repair manual showing the correct torque. However, that is a good idea to tighten the plug. I am showing ignorance here, but is it abnormal for a fair amount of oil to be coming from a cylinder (regardless if the spark plug is tight or not)? Would oil in a cylinder be an indication of something terribly wrong, or is it normal for a certain amount of oil to be present?

You should try tighten the spark plugs first. You don't need torque wrench at this stage. If the oils bubble out, it might be loosing quite. Just turn with a spanner and see to have a peace of mind. If it is loose, just bring it to nearest mechanic to tighten with TW ASAP.

I tightened the #2 spark plug and started the car without #2 plug wire installed. I noticed that no more bubbles of oil are appearing in the spark plug tube. I re-installed #2 plug wire and car runs better but is still running rough. I will have my mechanic pull the spark plug when the car goes in the shop later this week. Between now and then, I will monitor the spark plug tube to see if any more oil appears.

Can anyone tell me (if the oil is not coming from a leaking valve cover gasket)... IS IT NORMAL FOR A FAIR AMOUNT OF OIL TO BE PRESENT IN THE CYLINDER - ENOUGH THAT COULD BUBBLE-OUT IF THE SPARK PLUG IS NOT TIGHT? I am trying to get a feel for if I have a serious problem with the engine, or if it is normal for some oil to be present in the cylinder. THANKS!