Reader David Bennett recently wrote in, asking about oil temperature vs. oil grade.
“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°F to 90°F, but on the Aeroshell site, it says 0°F to 70°F. Which is right?”
Temperature vs. oil viscosity is important at both start-up and cruise. 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. This can increase the wear rate and reduce engine life.