让你去换机油是为了卖其他service

大部分换油周期都偏保守，根本不需要那么频繁

行业内自己说了是为了卖其他service

https://www.edmunds.com/car-news/tips-advice/stop-changing-your-oil.html

Another National Oil and Lube News article tied the frequency of oil changes to success in pushing related products and services. For a midsize SUV, the stepped-up oil change intervals will bring in $1,800 over the life of the car, the article says. "A few extra services [or oil changes] can go a long way toward increasing the amount of money a customer will spend during the lifespan we estimated here," the article concludes.

http://www.nytimes.com/2010/09/11/your-money/11shortcuts.html