The 710 oil cap mystery has a wonderfully low-tech answer: turn the picture upside down. What looks like a number is meant to be the word OIL, viewed from the wrong direction. The missing car part in the joke is an oil filler cap.
There, the answer is yours without a long wait. The fun is in how the misunderstanding works—and why a tiny change in viewpoint can make an apparently baffling request suddenly obvious.
The source presents this as an amusing story, not documented reporting about a particular customer or repair shop. Its continuation page supplies the punchline. Below is the complete small joke, followed by some useful context that stays separate from the story itself.
The Complete 710 Oil Cap Joke
A woman wants a replacement part for her car but cannot remember its name. She remembers what seems to be “710” written on the missing cap, so that is the description she brings to an auto parts store.
To make the request clearer, she draws the mysterious part. Someone turns her drawing upside down. The apparent number becomes a word, and the confusion disappears: she has been looking for an oil cap.
That is the full payoff supplied by the source. There is no named mechanic, repair bill, quoted exchange, or later adventure to add. The joke works because the answer was present in her description all along, just facing the wrong way.
