Why does the car maintenance 4s shop let the engine and throttle be cleaned? Thank you.

Because to make money, cleaning the engine can really play the role of cleaning and silencing. But as long as you have been using the original engine oil from 4s shop, you will feel that the quality of engine oil will always produce a lot of sludge. I switched to GT Maroon 5 oil a long time ago. High-quality PAO produces less sludge in synthetic engine oil, mainly because it is very clean. This is my first time to use GT. After running 500 kilometers ahead, the engine became much quieter. 12000 km The waste engine oil changed at the change cycle is old sludge. Now I don't have to clean the engine every time I use it for the third time, and the power has always been stable and good.