[Ridenour]

How many miles? The main issue is that with regular the engine has "worked" the regular into grooves / scuffs, ect. and if you switch to something with a higher viscoscity, it could wash out those fillings / cause problems with compression, ect. These problems are varied, and there's no real rules about how many miles / what types, ect. It's just generally a bad idea to switch from regular oil to fully synthetic on any vehicle with significant miles. I would go to synthetic blend, honestly. It's not so harsh a change, but still gives you most the advantages of fully syth. I ran regular in my GA forever, and at about 37,000 miles I switched over to QS synth-blend "high rpm" oil, and have using that for the last 11,000 miles. No problems at all, and I swear it's helped a tiny bit with power. Just a tiny bit. The stuff's like water after it gets heated up.