We have a new-to-us '05 xc70 with about 173K miles on it. On a recent 500 mile round trip, a weird oil loss occurred. I checked the oil before leaving, and it was full. When I arrived at my destination (250 miles of mixed highway and interstate driving, mostly between 45-75 mph) and let the car sit overnight, it was about 1 quart low. I drove home, guessing that it would be a quart low when I arrived, but there appears to have been no oil loss on the return trip, though I took the same route and drove at similar speeds and in similar traffic. I'm baffled.

We have a '12 XC70 that we bought new - the oil level on the stick drove me crazy.

I too found that on a trip, it looked low but recovered.

Since we had two cars, I experimented with checking the oil at various times after the car was driven.

The book tells you to wait an hour.

I tried one hour, overnight, after a day, two days, three days.

My findings after trying this several times - is seems that sometimes the oil drains back to the sump in a reasonable time, and sometimes it takes several days!!!

This car does not use any oil.

I always reccommend a weekly oil level check.

I assume you are using synthetic oil, you better be. Did you also wait til the next morning to check the oil after the trip?

Have you checked the PCV for vacuum? Usually, long trips help to clean things up internally and your engine is probably happier now.
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Keeping it running is better than buying new

Absolutely using synthetic! Mobil 1 5w30 all the time, every (turbo) car (not using it on the NA v70 base). Haven't checked PCV for vacuum; howm might one do that? Thanks! I should have mentioned that there is a leak somewhere, as there is a constant drip under the car, but not the quart's worth on that trip. Car seems to run fine.

Do the latex glove test, I put a rubber band around the glove to hold it to the oil filler hole. It works best when the engine is warm, like 30 minutes after shutdown.

Then find the leak! It could be a cam seal or oil cooler line. Remove the bottom splash shield so the oil drip will pinpoint the leak.

Once, I had two crush washers on the oil drain plug. Oops!
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Keeping it running is better than buying new

A crude way to check your PCV to see if it is functioning properly is take the oil filler cap off and place a shop glove over the opening.

If the PCV is good it will attempt to suck the glove into the top of the cylinder where the CAMs are.

If the PCV is bad it will attempt to blow the glove up like a balloon. Usually you'll see it start to inflate and hang there limply. The really bad ones will blow right up. That's when you know you really need to replace the PCV.

Matt