Why is it necessary to change vehicle oil regularly, and not just change the filter and add new oil as needed?

Question

Why is it necessary to change vehicle oil regularly, and not just change the filter and add new oil as needed?

In: Engineering

Answer 1

ELI5 answer:

Firstly, engine oil is more than just oil. It has a bunch of other stuff (additives) to help clean the engine, protect from corrosion and neutralize any bad stuff that forms from the heat and byproducts of combustion.

Now to answer your question, the oil as well as the additives actually degrade and break down on a molecular level as they do their job. Oil thins out and can’t lubricate as well, and the additives all break down or get used up as they do their job protecting the engine.

That means you have to replace the old oil with fresh new oil periodically. That’s why you see pictures of 20 year old engines that look basically new inside because the owners changed the oil religiously.