As suggested, check your owners' manual and use a SAE weight oil that is recommended for the ambient temperature range the car will see over the interval that the oil will be in the car. High oil consumption does not lead to catastrophic failures and a broken ring will cause lots of blue smoke (despite the converter) and poor performance, but the engine won't quit. There's essentially no risk of a catastrophic failure due to the relatively high oil consumption.

If he's really concerned have a compression or leakdown test performed. If the numbers are good there is nothing to be concerned about. An engine can have excellent compression/leakdown numbers, but still have high oil consumption due to valve guide wear and/or deteriorated vavle seals. Bad guides or seals just cause high oil consumption, but don't necessarily cause any operational problems or reduce engine performance.

I replaced the valve guides on my Cosworth Vega two years ago when oil consumption degraded to a quart every 100-200 miles. The engine ran fine and had good compression and leakdown numbers. The OEM valve seals were never very good to begin with and the guides were severly worn. New guides and a new seal design that I found reduced oil consumption to a quart every 5000 miles. Despite the severe valve guide wear, there was no measureable wear on the aluminum/silicon cylinder bores.

In 1979 a friend of mine bought a new Porsche 911 SC, and it used a quart every 600 miles from the get-go. Porsche said it was within the normal and acceptable range!

Duke