Proper maintenance.
 

20w-50 in summer, 10w-40 winter.
99% of the oil out there has 'detergent' in it to help keep the engine clean.

If you change it regularly at 3-4k miles, the engine will stay clean inside.

Same goes for anti-freeze. Its cheap enough to change every other year. Helps keep the corrosion from building up.

Same with diff oil, and power steering, and tranny, too.

I don't know about that...

I'm using Mobil Delvac1 5w40 in my Subaru and changing the oil every 10k or so. I'll be changing the filter at 5k and sending an oil sample out for analysis just to make sure everything is fine and dandy.

Just think... use a good quality oil, Mobil 1 or the like, and a bypass setup with submicronic depth filter, and you'll never have to change your oil again. Just the filters, and add oil as necessary due to leakage, or burn, but also to freshen up the additive packets.