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Ask Paul: Is This Engine at Risk of Failure?

Ask Paul: Is This Engine at Risk of Failure?
Evaluating Cylinder Head Temperatures in a Piper PA-24 Comanche
Julie Mangold, owner of an aviation company specializing in drone chase services in Southern California, has raised concerns regarding the cylinder head temperatures (CHTs) of her Piper PA-24 Comanche 260B. She reports that during climbs, the CHTs on cylinders 5 and 6 reach 445°F, subsequently cooling to approximately 400°F during cruise. With 1,890 hours since the engine’s major overhaul, the powerplant otherwise performs reliably. However, her younger commercial pilots have expressed apprehension, describing the engine as a “ticking time bomb.” Julie seeks guidance on whether these temperature readings are within acceptable limits and how best to address her pilots’ concerns.
Paul McBride, an expert on general aviation engines, provides a detailed response. Assuming the aircraft is equipped with the Lycoming IO-540-D4A5 engine, the operator’s manual specifies a maximum allowable CHT of 500°F, with recommended continuous operation between 400°F and 435°F to ensure extended cylinder life. Based on Julie’s reported figures, the engine is operating within these prescribed parameters.
Paul emphasizes the importance of pilots consulting the engine operator’s manual to understand manufacturer guidelines thoroughly. For operators lacking a manual, he advises obtaining one—specifically part number 60297-10—from a Lycoming distributor or directly from the factory. He also highlights a common issue in aging aircraft: the potential inaccuracy of engine instruments due to gauge drift over time. Since Julie’s maintenance team has already inspected and adjusted the engine baffling, which plays a critical role in managing CHTs, Paul recommends verifying temperature readings with a calibrated instrument to confirm their accuracy.
With nearly 1,900 hours since overhaul, the engine’s condition reflects diligent maintenance practices. Paul advises continuing routine oil and filter changes and prioritizing pilot education on proper engine monitoring and data interpretation to maintain operational safety and confidence.
Broader Industry Context and Implications
Concerns about mechanical reliability extend beyond aviation into the wider transportation sector. The National Highway Traffic Safety Administration (NHTSA) is currently investigating over 1.1 million Ram pickup trucks for potential transmission failures following a recall, raising questions about long-term dependability and prompting heightened scrutiny. Similarly, Nissan recently recalled nearly 444,000 vehicles due to possible VC-Turbo engine failures, efforts that underscore the competitive pressures manufacturers face to assure consumers of their products’ reliability.
These automotive challenges coincide with the upcoming 2025 Japan Mobility Show, where the industry confronts significant pressures from rapid technological advancements and international trade tensions. Although these issues are specific to the automotive field, they highlight universal themes relevant to aviation: the critical importance of rigorous maintenance, precise diagnostics, and transparent communication to uphold safety and trust.
Conclusion
Julie’s engine is operating within manufacturer specifications for cylinder head temperatures. With continued adherence to maintenance protocols and verification of instrument accuracy, there is no immediate cause for concern. This situation presents an opportunity to reinforce best practices among pilots, fostering both safety and confidence in the performance of the fleet.

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