In college, one of my favorite courses was internal combustion engines taught by Prof. Groves. One semester, the main topic of the course was the differences between spark ignition (SI) and compression ignition (CI) engines. After taking the final test, on which we were to compare the advantages of the SI and CI engines, I stopped to talk to Groves, along with several other students. While we were talking in the hall, another student came up and asked, “What does SI and CI stand for?” I remember Groves just hitting his head against the wall and shaking his head.
I feel this way sometimes when someone asks me, “I was working on my plane recently and did not have any aviation grease, so I used some automotive wheel bearing grease. Is that OK?” Unfortunately, people jump to the conclusion that if it does the same job in an automobile as in an airplane, they should be the same. This logic may or may not work — and if it doesn’t, you can have serious problems.