The cylinder head temperatures for my Lycoming O-320 engine runs about 320 degrees in standard conditions at cruise power. I have seen it as hot as 405 on a long climb when heavily loaded, but even that temperature is well below any cautionary range. I often take-off from the house and maintain full-power for 15-20 minutes while I climb up to the the desired altitude. Imagine pulling onto a road in your truck and putting the gas pedal on the floor for 20 minutes, it seems like that may cause some mechanical issues over time. A naturally-aspirated reciprocating engine, like my O-320, was certified for 2000 hours of continuous, full power (2750 RPM) operations. It was actually designed to operate under full-power for the entire life of the engine … that is pretty awesome. Even more amazing is that it is technology from the 1940’s. In-fact the mechanism that makes the spark for combustion is called a magneto, the same contraption that made the spark for tractors almost a century ago (magnetos were first used by Daimler in 1899). These simple little 4 cylinder 160 horsepower engines are incredible pieces of machinery with a nearly perfect record. To purchase a new engine from the Lycoming factory costs nearly $30,000. A complete rebuild typically costs about $10,000 if I do the work myself.
I believe this image was taken as I was descending out of 8,000′ after a long hard climb. As I mentioned above, an engine will build a fair amount of heat in a climb, and it is careless to simply, chop the throttle and descend quickly for landing. When the throttle is reduced the amount of heat being produced is decreased, and the increased airflow caused by the descent may “super-cool” the engine. Super-cooling becomes a problem when the different types of metals in the engine expand and contract at different rates due to rapid temperature changes. This can lead to visible cracking of the cylinder head and that is the sort of thing that can ruin my day. A crack very seldom causes catastrophic failure, but it can cause serious wallet damage. I was slowly descending while circling above my desired landing point on the Nelchina Glacier in the Chugach Mountains when a mountaineer zoomed in on the Super Cub and snapped this picture.