Car engine oil both cleans and lubricates your engine. It’s a bit like what blood does for your body, cooling, cleaning and protecting the engine’s internal components. Engine oil is only needed for vehicles with an internal combustion engine (ICE); battery electric vehicles (BEV) don’t need engine oil.
The main function of oil is to lubricate moving parts within the engine. These include the:
The oil forms a thin protective layer between these components that reduces friction, and therefore reduces wear. If there was no oil, there would be metal-on-metal contact which would cause the engine to seize up within a few kilometers as it overheated the metal.
Even thought the oil forms a lubricating layer on the metal components, small metal particles, dirt and debris can accumulate in the engine. Engine oil contains compounds that keep these contaminants in suspension in the oil, preventing them from causing additional wear by settling on engine components. As the oil is passed around the engine, it eventually ends up at the oil filter which traps the bigger particles. Over time, the microscopic particles in the oil turn the oil a different shade.
It also absorbs and neutralises acids produced as the fuel burns.
Metal on metal friction would create enormous amounts of heat, therefore oil plays a critical role in cooling the engine. As well as its lubricating properties, it absorbs heat from hot engine components and dissipates it in the oil pan where it is transferred to the surrounding air or passed through an oil cooler. This is one of the temperature regulation methods within an engine.
Corrosion and rust
As well as detergents that suspend particles in the oil, oil contains anti-corrosion compounds that stop internal engine components from corroding or going rusty. When the engine is in use, corrosion isn’t a problem; oil comes into its own when the engine is at rest for longer periods.
There has to be a seal between the pistons and cylinder walls for efficient combustion. Oil helps form a proper seal by forming a thin barrier that stops combustion gases escaping into the crankcase. If that happened, the engine would experience a loss of power and would have a smoky exhaust.