View Full Version : Subaru outback-oil leaking out spark plug boots - how critical?

11-12-2008, 10:49 AM
The last 3 or 4 days, my Subaru Outback was stuttering at low RPM and the check engine light came on yesterday. I picked up some new spark plugs and installed them last night, and the old ones were pretty burnt so hopefully I've solved that issue. Seemed to run fine this morning.

When I pulled the spark plug boots, they came out with oil on them. I've never worked on a vehicle with the spark plug boots going through the valve covers like they do on this car, but this doesn't seem right. I looked in my Haynes manual, and apparently there are seals inside the valve cover, which I assume are to prevent this. Judging by the stains on the valve covers, it looks like a small amount of oil has been leaking out for a while, but not enough that I've seen a significant loss of oil.

My questions are:
Am I right that the seals inside the valve covers are supposed to prevent this?

If it's a slow leak is it critical that I replace these soon? If not, I'd like to wait until next spring when it's warm out to replace them, as I'm working outside, and VT's a little nippy this time of year.

Gary T
11-12-2008, 11:02 AM
Yes, the valve cover gaskets, which include spark plug well seals, are meant to keep the oil inside the engine and out of the plug wells.

While it's not a critical problem (the oil won't affect spark plug performance), the oil will be absorbed by the rubber spark plug boots and they will swell. The boots are part of the plug wire assemblies, and you may save having to replace the plug wire set by fixing the oil leak sooner rather than later. However, if the vehicle has in the neighborhood of 100,000 miles, it's not a bad idea to replace the plug wires anyway as a preventive maintenance.

11-12-2008, 12:09 PM
Thanks Gary T!

I don't have quite that much mileage on the car yet - it's around 75K, but I was considering replacing the plug wires anyway. If that's all it's going to damage, I'll probaly just keep an eye on it and wait until Spring to give her a tune-up.

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