"That's an oft-reported myth"

Is going past TBO more expensive? Plus fuel vents and turbocharger temps. Email [email protected] for a chance to get on the show.

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Full episode notes below:

Mike wonders if running past TBO actually costs more. He has a Mooney and has heard that overhauls far beyond TBO can cost more as a result of having to replace more parts. That is an oft-reported myth, Mike says. The only things that can cause an up charge on most field overhauls are having to replace the case or the crankshaft. Otherwise it’s a fixed price. Paul says the top engine generally goes into the trash. On the crankshaft, they usually just have to polish it or grind it. There’s no repairing a crankshaft. If it’s bad, it was bad because it had some other type of problem. You can go thousands of hours on crankshafts. Mike said Lycoming had a white paper on their website that said crankshafts are generally good for 14,000 hours. Cracks on the case can be welded.

Mark has an early 182 and he’s having issues with the fuel caps properly venting. He has noticed that once you fill the tanks with cold fuel, there doesn’t appear to be an outflow vent. Paul said there’s a small weep hole that allows the expanded fuel to vent. But Mark’s tanks still aren’t venting. He pulled it out but didn’t seem to find a weep hole. He said it looks original and has an early Cessna part number. If the fuel is pouring out it needs to be replaced because the check valve is bad. The wing will balloon and can cause structural damage without a weep hole. He said when he removes the cap a big woosh of air will come out, indicating the fuel isn’t venting out as it expands.

Jim is wondering how TIT and EGT intersect. He flies a turbo Saratoga and has been experimenting lean of peak and rich of peak. He’s noticed a significant difference between EGT and TIT. If the TIT is farther away from the engine, he’s wondering why it’s hotter than EGT. He’s also wondering how hot he can let the turbocharger get. Mike said TIT is hotter because the EGT probe is only seeing gas flow for less than a third of the time, and only when the exhaust valve is open. The EGT probe actually measures a “probe” temperature that averages the temps over time. When the gas gets to the TIT probe it’s a constant heat from all cylinders all the time. Redline on his TIT is 1,650 degrees, which Mike said is a continuous operation limit. Paul asked what the exhaust system is made of because that matters. He suggests not exceeding the red line. In cruise, the lower you can keep the TITs, the longer the system will last. Mike limits his TIT to 1,600.