We all get all sorts of advice from people who think they know about cars. Sometimes it’s tough to tell what’s true and what’s been made up. Unfortunately, it’s pretty common for bad advice to SOUND legit, and then get passed down from generation to generation.
For example, most people think that changing the oil is a must at 3000 miles. This was true in the past, but modern engines can go much longer. You’re safe changing every 6k. Sorry, Pep Boys.
One that I always did wrong was filling my tires to the max pressure level. I thought it would help gas millage. Turns out, I’ve been filling up my tires TOO much. You really need to fill to the inflate level, not the max.