Technical Oil on spark plug threads

Always wondered how or why oil gets on the spark plug threads. When I pull the plugs, the threads are wet with oil. Anyone?

 

If it's oil , & not unburned fuel , you have excess oil in the combustion chamber ,rings , valve guides, or intake gaskets ....
dave

 

I've always wondered about that too. The rest of the combustion chamber and end of the plug can be dry, but oil seems to wick up into the threads, even on healthy engines.

My guess is that some oil is sucked into the combustion chamber and it stays on the threads because it isn't subjected to burning away in there.

Don

 

I use a bit of anti seize on every plug I install. When they are eventually removed that might look a little like oil with the dirt from combustion.

 

Have wondered about that too, thought caused by maybe the valve covers leaking but that's not it. Definitely minimized if tuned up right. Betcha it's from lots of short trips, like everything else.

 

This is one of those things that I accept as a part of nature...not something to worry about.

 

I use Milk of Magnesia (sp?) on aluminum heads...

 

Oil on the spark plug threads is classic leaking valve covers, only it`s leaking so lightly you can`t tell. What`s the only oil source above the spark plugs? the heads, and where`s oil going to go once it`s leaked out? down due to gravity.

That's my story and I'm sticking to it.

 

Champion makes a conductive anti-sieze spark plug thread coating for aircraft, comes in a little bottle with a brush on the cap - I got it at Aircraft Spruce. It's black so I guess I never knew if I had oil on the plug threads...............

 

mix that with vodka and you get a Phillips Screw Driver.

I have never been overly concerned with a little oil wicking on the plug threads personally. I doubt it is cause for alarm, IMO.

 

I run mechanical injectors on the street and often wondered if it's actually fuel or really oil? I have to run it fat to compensate for no accelerator pump.

 

Mine's a flathead, so no leaking from a valve cover here. The plugs are above the heads instead of your idea. What causes my oil on the threads?

 

For an OHV car, I completely agree.

 

kind of like the oil we find when we pull a dry nozzle or Injector on a diesel ( injector/nozzle mounted on exterior of block not under valve cover ) , the thread seal is not as tight as one thinks ( expansion and contraction of the metal and stretched threads from not using a torque wrench ) and when the chamber pressurizes the plug/injector moves on the threads and it pushes a little of the charge past the threads and then cooks to a carbony varnish .. the EMDs I work on the test plugs ( drains used to drain any water in the cylinder from being deadlined ) on the cylinders always have a little brown goo on them and they have a tight seal ... but I did have a Dart ( 190 ) that the plug tubes were filled with oil all the time till I found the rust out hole in the bottom of it ..

 

Means you got no heat. Typical street deal not a big thing. Lippy

 

It's kind of one those things like where does all the rubber that wears off of tires go. You'd think there would be piles of rubber particles on the shoulders of the roads.

 

how can you have oil around the plugs ?? you launch them things ...

 

Remember not all the gas burns 100%. So all the pressure generated on the power stroke pushes gas up the threads. Since the engine is running under heat and pressure
you have a small refinery there and the hydrocarbons in the gas are converted back to oil

 

That sounds just technical enough to be right! Add to that that many of the motors that have oil on the plug threads are high compression, have high lift, long duration cams, or are multiple carb motors, we don't seem to notice it much on the average daily driver (or we don't pay much attention to them). Gene

 

So it's not really oil but unburnt fuel pushed up into the threads from compression?

 

Yep !
dave

 

I think its cyl. pressure and the combustion explosion pressure, kinda same way a 55 gallon drum will wick water off the top of drum through the tight sealed bungs.
Temp changes make it pressurize and also pull vacuum at different times and water will get past the bung seal and threads.
In this case its probably very very slight oil in fuel from rings, valve seals etc and over time, plug threads get saturated from bottom up. Spark plug washer is on outside of engine, threads are inside of engine and via expansion and contraction , it seeps from there out to the goofy plug washer/seal.

edit: read rest of thread, Stimpys got it!

 

You are 100% correct. Oil and just about any element can be taken apart and put back together again in a large number of ways. The rubber worn from tires turns to dust blowing in the wind. Its recycled by the planet.

 

Thanks for feedback everyone, I thought my engine was beginning to go south...