Oil getting on spark plug threads - Fuel Economy, Hypermiling, EcoModding News and Forum

Cd · 07-01-2009, 04:48 PM

I replaced the valve cover gasket and plug gaskets on my '93 Civic, yet there is still a huge amount of oil on the threads of the plugs when I pull them out.
What's happening, and what do I need to do to fix it ?
What's the damage$ .

I notice that the cars acceleration is very weak, but otherwise, the car runs flawlessly.

Clev · 07-01-2009, 05:04 PM

I can't dig up the link I saved, but on my Accord, there are two sets of o-rings that keep the oil out of the spark plug tube. One set comes with the valve cover gasket set, which sounds like the ones you replaced. The others are further in the head and require removing parts (rocker arms?) I would assume that the Civic uses a similar design.

Thanks for reminding me--I'm having my timing belt done in about 3,500 miles and I'll make sure they replace those as well.

Christ · 07-01-2009, 05:23 PM

Yes, the Civic uses the same design, and you can replace the gaskets below the spark plug tubes with silicone, or just get the new gasket from a dealer, it's only a couple dollars.

Cd · 07-01-2009, 10:10 PM

What if it is not the gasket and 'spill-over ' as the mechanic that I go to suggested ?
The slow acceleration is one of the supposed symtoms of this.

Christ · 07-01-2009, 10:26 PM

Spill over? Not possible.

Where would it spill from, if you get all your oil in the oil fill hole? The spark plug covers are closed except a small vent on some aftermarket wires, there is a gasket between the head (valve) cover and the spark plug tubes, which you just replaced. There are also gaskets between the bottoms of the tubes and the head itself. There is no place where "spill over" is actually possible.

No offense, but please find a mechanic that either explains things better, or isn't going to give you a BS answer when he doesn't know something.

Although, he might have been saying something other than what I'm getting from the term he used... if that's the case, he should explain a bit better what he's actually talking about.

Christ · 07-01-2009, 10:31 PM

He may have been referring to "blow-by" which is a condition where rings don't seal, thus, combustion pressure blows into the crankcase, and oil gets sprayed up into the combustion chamber of other cylinders, which incorrectly describes your condition.

I presume that what's happening to you is that oil is getting on the upper part of the spark plug. You can verify a tube seal leak (upper seals or lower gaskets) by thoroughly cleaning all the tubes after pulling the plugs, cranking the engine over without the distributor plugged in to clear the cylinders of oil and whatever you put in to clean the tubes, then run it for awhile and swap the tubes with q-tips to check for oil before you remove the plugs.

Usually, you can also see evidence of oil leaking into the tube seals on the plug wires themselves, which have rubber sealing boots on them, and are about 3-4" long.

Cd · 07-03-2009, 04:44 PM

Whuups !
I meant "blow-by ".

The spark plug has a large amount of oil on the threads when I remove it, yet the spark plug wire boot is spotless. ( Also the tubes are clean on the sides .)
I don't understand where that the oil is coming from.
Also, I don't understand how that oil could seep into the threads like that, unless it leaks downwards as remove the plug. ( The plug is screwed in very tightly.)

This sounds like the ring seal problem that you were describing.
My car is very sluggish, yet the F.E. seems normal ( around 38 MPG, with over 45 MPG on the highway on a nice long trip. This is with an automatic. )
I have been thinking that if something was wrong with the car, that the mileage would drop. I guess this is not the case.
Also, I might add that I passed my emissions test easily. If oil is getting mixed into the engine where it shouldn't be, wouldn't this cause more pollution ?

Thanks !

Christ · 07-03-2009, 05:23 PM

Quote:

Originally Posted by Cd

Whuups !
I meant "blow-by ".

The spark plug has a large amount of oil on the threads when I remove it, yet the spark plug wire boot is spotless. ( Also the tubes are clean on the sides .)
I don't understand where that the oil is coming from.
Also, I don't understand how that oil could seep into the threads like that, unless it leaks downwards as remove the plug. ( The plug is screwed in very tightly.)

This sounds like the ring seal problem that you were describing.
My car is very sluggish, yet the F.E. seems normal ( around 38 MPG, with over 45 MPG on the highway on a nice long trip. This is with an automatic. )
I have been thinking that if something was wrong with the car, that the mileage would drop. I guess this is not the case.
Also, I might add that I passed my emissions test easily. If oil is getting mixed into the engine where it shouldn't be, wouldn't this cause more pollution ?

Thanks !

Blow-by is common for lack of power, but is also a cause of oil burning. If you don't have both, you don't have blow-by.

Oil on the spark plug threads would only happen as a result of blow-by if you're using an incorrect length plug. The threads are normally covered, except maybe the last 2-3 closest to the electrode.

The only way that oil will get on the threads is while you're pulling the plugs out, and then only if there's a leak in the lower tube seal.

Oil on the boot itself indicates and upper seal leak, no oil on the boot, or only on the tip of the boot, indicates a lower seal leak. It's not to worry about, honestly.

As for your lack of acceleration power, do a compression test first of all. The tester is only about $20, and it's the first diagnosis tool besides a vacuum gauge that most people will need.

clarkperez2334 · 08-26-2010, 02:31 AM

I think this is an oil fouled condition of the spark plug commonly caused by cylinder walls that are faultily worn. Oil may be pulled into the chamber because of intense clearance in the valve stem guide. When the PCV valve is plugged or is not working this could result to a buildup of crankcase pressure. This condition can force oil vapors and oil past the rings and valve guides into the combustion chamber.

This condition of a spark plug shorted by excessive oil entering the combustion chamber is commonly known as Oil Fouled.

some_other_dave · 08-26-2010, 06:42 PM

Fouled plugs usually have a black tar-like substance on the electrodes, not liquid oil on the threads.

Since the plugs go (more or less) straight downward into the chambers, it is unlikely for any decent amount of liquid oil to stay on them. It is much more likely that there is some liquid oil getting into the bottom of the spark plug bores past the lower seal. Then when the plug is removed, that oil wicks onto the plug threads.

My CRX has a similar problem, but more severe. The end of the plastic connector on the plug wire is wet with oil, and there is a noticeable amount on the hex-shaped part of the plug itself. And the threads.

-soD