Prop hubs that were nearly scrapped, how to properly measure the oil level, semi-synthetic oils, and tachs that don't agree are on tap for this episode. Email [email protected] for a chance to get on the show. Join the world's largest aviation community today at www.aopa.org/join Full notes below: Bill has a Cessna 182 with a prop that hadn’t been overhauled for about 7 years and 600 hours. This past March he had to send the engine off for some work, and he decided to send the prop off at the same time. They told him the hub was close to being trashed because of corrosion. He’s worried if he had gone another year the prop would have been scrapped, and he’s wondering what he can do to maintain the hub. Paul said he regularly sends out props that are 12 years old and he’s never had a hub rejected, but Colleen said her hub was rejected for corrosion. Mike thinks prop shops are zero tolerance outfits. He said just because they find something wrong with it doesn’t mean it was unsafe. Prop failures just don’t seem to be a problem, the hosts agree. The bottom line: don't send out your prop unless you absolutely have to. Tate is wondering how to accurately measure his engine’s oil level. He suspects that we add oil more often than is necessary because many of us check the level after flying, and seeing it lower, think that we’ve burned oil during the flight. Paul recommends picking a consistent interval to determine oil consumption, ideally at least 24 hours after shutting down. He said if you check the oil level right after shutting down and it says 6, you probably have 7 or 7.5 quarts. Mike said the only way to check consumption accurately is to check how many quarts you add over the course of an oil change interval because that’s averaged over many more hours. Rex is trying to avoid sludge in his engine and knows synthetic oils cause problems, but he’s curious about semi-synthetic oils. Mike said it’s more of a concern in Continentals than Lycomings. He recommends if Rex wants to do that he stick to unleaded fuel. He is considering running 50 percent mineral oil to compensate for the problem of keeping the solids in suspension. The original tachometer and the tach in Pete’s JPI run at different speeds. After many years of operation there’s now a big difference in time between the JPI and the mechanical tach. He wants to know which time to use for maintenance and aircraft valuation. Always use whatever time runs the slowest, Mike says.