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Old 04-29-2007, 12:00 PM
Join Date: Aug 2003
Location: BC, Canada
Posts: 1,667
Oily sparkplugs - how serious?

My husband changed my car's sparkplugs & wires yesterday. He said at least 3 of the 4 plugs were oily.

a) what caused this?
b) is it a serious problem?

(If it matters, it's a 1990 Honda Accord, 5 spd)
Old 04-29-2007, 12:32 PM
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Join Date: Aug 1999
Posts: 16,451
Oil can get into the cylinders from only a couple of sources.
Leaky intake valve guides, which allow oil to run down the stem of the valve and into the combustion chamber.
Worn piston rings which allow oil to get past them and into the combustion chamber.
Consequences? many. Exhaust may smoke, converter may be come fouled and not operate, EGR can become plugged, engine will use oil, and car might fail Air Care inspection. All of the above depend on the severity of the problem.
How hard to fix? (On a scale of 1-10 with one being no problem, I'll do it right now, at no charge and 10 being Holy fuck are you kidding) I would put the valve guides at a 4-6 and new rings at a solid 9. In fact if it is bad rings, it might be easier and cheaper to replace the entire motor rather than repair the one you have.
Only a proper diagnosis will tell from where the oil is coming from.
Old 04-29-2007, 01:33 PM
Join Date: Oct 2005
Location: The great PNW.
Posts: 3,636
Rick is probably right, but let me take another tack here. When you say oil on the plugs, are you talking about the bottom of the plug, the part that goes inside the engine, or are you talking about the top of the plug that is outside the engine?
Secondly, is it really oil, or is it black stuff? Because it could be carbon, which might be caused by a bad fuel/air ratio, i.e: too much gas.
If Rick is right, it's likely that you're having to add oil to the engine between oil changes.
Old 04-29-2007, 02:02 PM
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Join Date: Aug 1999
Posts: 16,451
I will be honest with you, I did not consider an oil leak into the spark plug wells, and that the oil might be on the top of the plug.
Here are some pictures of common spark plug conditions. Their example of oil fouling is not very extreme. This is more what I think of, when I think oil fouled.
Are these what your husband saw?

Last edited by Rick; 04-29-2007 at 02:04 PM. Reason: fixed link
Old 04-29-2007, 02:50 PM
Join Date: Mar 2002
Location: KCMO
Posts: 11,216
I'd say it's almost a certainty* that he saw oil on the exterior portion of the plugs. The cause is leakage past the spark plug well seals in the valve cover. The cure is to replace the valve cover gasket and plug well seals.

It's not especially serious. It's an engine oil leak, so there will be some oil loss. The oil will not affect spark plug operation, but it will (if it hasn't already) damage the spark plug wire boots. Not very expensive, certainly worth fixing.


*Why? Because plug well seal leakage is quite common, valve stem seal leakage much less so, ring leakage very much less so; and because oil-fouled spark plugs usually look more sooty than oily, whereas this condition definitely and clearly looks like oil on the (outside of) the spark plugs.
Old 04-29-2007, 03:47 PM
Join Date: Aug 2003
Location: BC, Canada
Posts: 1,667
He says it is definitely oil, and that he saw it on the white ceramic(?) part of the plug as well as the bottom.

We don't have to add oil between changes normally, but this time we put off the oil change longer than recommended, so we DID need to add a couple of litres recently.

I'm hoping Gary T is right and that it will be a fairly easy fix.

I'll ask my husband, McDeath_the_Mad to post more details if he has 'em.

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