How oil works in a car's engine

inside of engine
inside of engine

They say oil is the lifeblood of an engine, but you might be surprised at just how accurate this statement is.

When most people think of the role of oil in cars, they will instinctively focus on the fuel that propels their vehicle.

But while petrol and diesel are both by-products, oil in its purest form functions as a lubricant.

Just as blood gives life to your body, the correct oil lubrication gives life to an engine.

An engine’s lubrication system consists of a sump (where the bulk of oil is stored), oil galleries (just like veins that transport blood through your body), an oil pump (essentially the heart of the matter) and finally, the filter (like kidneys, this removes any impurities from the oil before it is pumped through the motor).

As oil is pumped through the engine under pressure, it leaves behind it a special lubricating film (oil film) that creates a slippery surface (or slip effect) over everything it touches.

The primary job of oil film lubrication is to ensure the engines components move smoothly, while minimising friction and component wear all at the same time.

The end result is increased engine performance and service life.

Amongst many other tasks of an engine oil, its role as a heat transfer is possibility the toughest.

Engine oil transfers heat away from lubricated engine components such as bearings, pistons, rings, valve stems and cylinder bores during operation.

As the oil travels around the motor, more and more heat is absorbed and transferred.

Upon arrival back in the engine sump, the oil is cooled by the external air that travels over the surface of the sump before being re-circulated back through the system for further duties.

This all happens simultaneously while also softening the blow of engine vibration through providing the cushion of oil lubrication.

But that's not the only function of the so-called 'black and gold'.

Engine oils - whether mineral, semi or full synthetic based are equipped with additives such as friction modifiers and special detergents or cleaning agents. 

These additives improve operating efficiencies as they prevent the internal build-up of varnishes and deposits.

Detergent additive molecules work to disperse larger deposits while preventing smaller particles such as carbon deposits from grouping together, otherwise known as sludging.

But it's a short-term solution: while oil will always lubricate, its ability to protect items such as oil seals and components over the long term is reduced through these everyday functions.

Oil protection levels deteriorate through contamination, which is brought about by droplets of fuel leaking past the piston rings and landing in the engine's sump.

This adds to this internal component wear, producing microscopic particles and ultimately engine heat.

These microscopic wear particles simply float around in the engine's oil until they are eventually caught by the filter, which becomes clogged and less effective over time.

It is this contamination that reduces the oil's effectiveness to protect, which incidentally also includes the breakdown of the all-important lubricating oil film protection

A telltale sign of this contamination is the colour of the oil: typically gold and translucent when new, it is turned black and opaque by these various processes.

Manufacturers can anticipate roughly how long it will take for this process to occur and it is a major factor in setting the servicing schedules on cars by time and mileage, where oil and filters are replaced.

But maintenance routines are rarely dictated beyond the end of the new car warranty, which is one of the main reasons why you should get your vehicle serviced regularly on your own initiative.

The first step for any good mechanic is judging the correct engine oil grade selection: known as viscosity, is vital to the performance and efficiency of any car's engine.

Too thick and it will take longer to pump through the engine, too thin and its ability to lubricate and protection may be less under heavier engine load conditions.

The age of your engine is also a factor, so be sure to use oil with the correct viscosity rating for the technology under the bonnet: check our earlier article on oil types to find out more about this.

Engine wear is at its highest within the first two minutes of operation and different oil types require different motoring strategies during this critical time.

Synthetic engine oils contain reach through the motor much faster than purely mineral-based oils, for a faster engine warm up time minimising engine wear.

Full and semi-synthetic oils feature additives that increase the integrity of lubrication within oil by literally leaving a Teflon-based coating over all components.

This is why it's fine to drive a modern car straight after ignition (at steady revs) rather than letting it warm up at idle.

Older model engines require that full warm-up procedure because they take longer to circulate mineral-based oils through engines: they must be operating within the correct operating temperature for the engine to be properly protected on the move.

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