I also have received several questions concerning the use of preservative oils. This seems to give the best combination of good starting and best high temperature protection. This goes back to my recommendation to use the grade 100 oil, or 80 if recommended, for most of your summer flying and then switch to a multi-grade during the winter or colder months. You do not want to be flying in hot temperatures with too thin of an oil. However, under warm conditions, you want a thicker oil to ensure that you have adequate oil film thickness in critical bearings and wear surfaces. If your oil is too thick under severe cold, you can experience oil cooler plugging. The other concern is temperature at cruise conditions. When most of your start-ups are at or near freezing (32☏), switch to a lower grade or multi-grade oil. The rule of thumb that I would recommend is to use the recommended SAE grade single grade oil for the warm summer months. However, on smaller Teledyne Continental Motors engines and some others, a grade 80 or SAE 40 oil is recommended for most warm weather conditions. Most engines recommend using a SAE 50 or grade 100 oil for most warm weather conditions. To determine which oil to use, consult your handbook or engine manufacturer. If your plane is in a heated hangar, that is the ambient temperature. If your plane is sitting outside, that is the temperature of your engine. The temperature to be concerned with is the ambient temperature of the engine at start-up. This can increase the wear rate and reduce engine life. If the oil is too thick at start-up, it will increase the time from when the engine first turns to when oil reaches critical wear surfaces. oil viscosity is important at both start-up and cruise. “When oil is rated for a certain temperature range, is that start-up temperature range or the range for most of the intended trip? My Super Cub handbook states SAE 40 is good from 30☏ to 90☏, but on the Aeroshell site, it says 0☏ to 70☏. Reader David Bennett recently wrote in, asking about oil temperature vs.
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