I can't quite remember the number, but I do believe a couple quarts every 5,000 miles is about the limit according to the manufacturer.
Personally I prefer to not have to add oil between oil changes. A quart every 1,000 miles more than doubles the oil I need to buy. At as much as 30,000 miles per year of be buying 30 quarts more than necessary per year. Not to mention oil consumption wreaks havoc on the catalytic converter.
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