No surprise that the companies who sell the oil say frequent changes are better. Here are our recommendations.

By Joseph E. (Jeb) Burnside

It’s accepted wisdom that your engine will last longer if you change the oil frequently. If that’s true—and we’re as guilty as anyone for supporting whatever mythology applies—isn’t changing it more frequently even better? And what the heck does "frequently" really mean? Engine manufacturers have their own recommendations, which are sometimes hard to find and even harder to follow. But as far as we can tell, these are determined less by actual research-based findings than they are textbook recommendations from engineering manuals. So for this report, we set out to find out what the piston-engine aviation oil professionals who manufacture and sell the oil and the people who analyze the…