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SEPTEMBER TECH NOTES ALLAN CALDWELL Technical Editor 28 Spiel – September 2021 AIR-COOLED 911 ENGINE OIL PRESSURE T he dry sump lubrication system used on air-cooled 911 engines continues to be unique among production road cars with its large supply of engine oil which is filtered and stored in a tank separate from the engine. Most models have twelve to thirteen quarts of oil that are continuously recirculated with only a small amount (on the order of two quarts) temporarily residing in the engine sump. As the 911 engine design evolved from the earliest 1965 2.0 liter models to the 1978-1983 3.0 and 1984-1989 3.2 liter models, a number of oil system features were upgraded including engine access covers, the crankcase oil pick up design, pressure relief valves, and eventually even the crankcase itself. With the continuation of our warmer, drier 2021 summer weather, our fall weather may be the ideal time to get that early air-cooled 911 out for scenic driving. Along with the single overhead cam engine design, the driver of the air-cooled 911 got an expanded display of five circular instruments to both entertain and worry the driver whether his engine is working correctly or not. Oil pressure, oil temperature, and oil quantity have always led the list of measurements that early 911 owners worry about. Once the oil pressure gauge appeared, the driver was faced with the problem of interpreting the value displayed by the gauge. Besides engine wear Table 1. Early 911 oil pressure specifications (data reference: Porsche Model spec books)