[brucepick]

I've been dealing with oil loss issues in my '97 Civic, about 230K miles.

A lot of my losses were through the valve stem seals and even the valve guides. It got bad enough that I got check engine lights all the time. I had a couple shops do a compression test and the second shop put a camera scope down the spark plug hole (into leaky cylinder) to look around, found a burned valve. Those scopes can't see the full circle of each valve in the cylinder but he did see the burned one. I decided to trust my rings, after filling the cylinders with Marvel Mystery Oil and after many days they were just as full as when I started. Be VERY careful dipping sticks into spark plug holes to dipstick the oil pool inside!!

So I had the head rebuilt. They replaced four of the 8 exhaust valves and all the valve guides. Of course all the valve seals too (rubber part). No more check engine lights and it runs very smooth after that.

It's still losing some oil. I noticed it on the bottom of the oil pan and suspected the oil pan gasket. However: I've seen it showing up the transmission housing, to the left of the engine. That oil is from the engine's rear main seal, which now likely has 230K miles on it, and 14 years. A pain to replace, but if you also need any clutch work you get access to both when you open up that area.

Early on, I tried many of the usual "fixes" for bad seals. Marvel Mystery oil, also Seafoam (not really for seals), Gunk engine flush (a thinning kerosene type treatment, you idle it 5 minutes to clean out stuff then drain all the oil + refill), and more. No luck with any of them. Also "high mileage" engine oils. No luck there either.

I've had some luck with two different "magic potions" in the oil that helped the rear main seal. Both are from Barr's, the radiator leak fixit people. The first was Barr's Rear Main Seal leak treatment, about $11 per bottle. That stuff worked pretty well. The labeling states in several places that it's specifically for leaky rear main seals. It's pretty thick but I'm sure it also uses additives that help it succeed. For the next oil change I used Barr's Engine Seal treatment, only about $4 per bottle. Helped but not as good; the results didn't last till the next oil change. Next time I'll use the Barr's rear main seal treatment instead.

Hope some of this helps!