Oil lubricates the moving parts of your engine. It keeps them cool by lowering friction and carrying heat away. It also keeps any grit or tiny particles from scratching tightly-fitted parts. So think of the oil in your engine as your vehicle’s lifeblood.
Heat breaks down oil. It can make the oil gummy or watery (or both), so that it doesn’t lubricate properly. And the longer it’s in the engine, the dirtier it gets.
Replacing old oil with new, fixes all these problems. The fresh oil lubricates and cools better. When you flush the old oil out…