Not 100% sure, but I was under the impression that if an engine were leaking oil, synthetic oil would just leak "better". If the engine is burning oil it's not a good to use synthetic either (probably a waste in terms of cost). Sometimes high mileage engines are prone to those problems. I still need to look into that...
a good synthetic can cure very minor leaks and decrease amount of oil burnt. If you're burning/leaking a quart a week then there's pretty much no hope.. but the higher quality oils can cure minor issues.
Car is drinking a quart between 3000 miles oil changes...Like my old protege 1992 and my altima 1993...Nothing to go crazy about! I'll see if syntetic will change anything to that!
You should also do an engine flush with your last crankcase of regular oil when you switch to synthetic to make sure to get rid of as many deposits as possible. The synthetics usually have better detergent qualities to them so you want to start as clean as possible so that your first crankcase of synthetic doesn't get filled with a bunch of leftover gunk. Amsoil has their own engine flush but you can use any brand as long as it cleans out the gunk. Run it for about 20 mins. at around 2000 rpm and then drain it immediately.
I swapped a 145,000 mile beater 5.0 over to synthetic oils. No problem.
The p5 has been getting Mobil 1 synthetic since new and 7-10K mile oil changes. Now at 224,000 miles and the thing still runs great, is perfectly clean inside, and I might use a quart in 10K miles.
