What is causing this spark plug to keep getting fouled with oil?

Dear Car Talk

Dear Car Talk | Mar 01, 1998

Dear Tom and Ray:

I have a 1987 Honda Civic wagon. Over the last few years I've had the valves and
rings replaced, oil seals replaced, head checked for cracks, and maybe more. I
can't remember. But the same problem keeps popping up. The number four spark
plug gets fouled with oil, and the car starts to run like a choo-choo train. If
I take out the plug, clean it or replace it, the car will run fine for a few
days, then it happens again. What's your diagnosis? -- Cynthia

TOM: Gee, Cynthia. If I had to guess, I'd say you have a bad number-four intake
valve guide.

RAY: The valve guide is the sleeve through which the valve stem slides when the
valve opens and closes.

TOM: And that valve guide (and the seal that surrounds it) is supposed to keep
the oil at the top of the engine from getting inside the cylinders. If the oil
does get inside a cylinder, it can do. . . what? Foul the spark plug! And that's
what I think is happening.

RAY: This assumes, of course, that the ring job you had was done correctly -- or
done at all. Because a car in need of a ring job could also foul the plugs.

TOM: But if the rings are good, then I'd look for a bad valve guide (or if
you're really lucky, just a bad valve guide seal), Cynthia. The guide will cost
you several hundred dollars to replace. Or, alternatively, pick yourself up a
good spark-plug wrench and a family-size bucket of spark plugs.

* * *
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