Why scheduled oil changes are important for your car

Arif · Jun 26, 2020 06:06 PM

The most “car maintenance” some us have done ourselves have probably been checking the engine oil dipstick, ATF dipstick, or at the very least, refilling the wiper fluid. Popping the hood is an unusual activity these days and is usually a sign of a broken car.

The late Irv Gordon clocked 3.2 million miles in his Volvo P1800

Good regular maintenance can extend the service life of your car, and there are many aspects of car maintenance that we can talk about. To keep things short, we’ll be focusing on engine oil changes. Things will get a bit nerdy.

We’ve already talked about the types of engine oils previously.

This is what happens when you don't change your engine oil for 130,000 km

Q: When do you actually need to change the engine oil of your car?

A: The answer is a simple one - follow the instruction manual of your car. Naturally, changing the engine oil also involves changing the engine oil filter. 

Q: What actually happens to the engine oil as you drive?

A: Engine oil is used to lubricate the engine. It lubricates and protects your crank, cylinders, pistons, and cams. The longer the engine runs (and the further you drive), the engine oil degrades.

Q: How does engine oil degrade?

Rough figures of viscosity deterioration of engine oil

A: There’s viscosity degradation, metal contamination, and soot contamination. There are also small traces of carbon deposits in the engine that further contaminate the engine oil. That’s why used oil looks darker than fresh oil.

Rough figures of metal contamination in engine oil

In my experience with diesel engines, we tend to observe a drop in lubricant viscosity as the operation hours increase. Research on gasoline engines also show a similar pattern of reduced viscosity with increased operation hours.

Q: How important is viscosity for an engine oil?

A: Very important. It is the characteristic that determines the engine protection levels. Hence, not changing the engine oil of your car will reduce its ability to protect your engine.

Q: What can you really tell by checking the oil dipstick?

A: You can tell your oil levels. That’s really as far as it goes for most of us. Engine oil generally turns darker as you use it.

Illustration by Lubrita

Q: Does synthetic oil really last longer than semi-synthetic and mineral oil?

A: Yes, definitely. Research published on the SAE* website suggests that. Synthetic oil degrades slower than mineral oil.

*SAE = Society of Automotive Engineers

Q: What are other benefits of using synthetic oil over mineral oil?

A: Synthetic oil has a lower volatility. It has less tendency to burn, and hence less tendency to react in high pressure and high temperature conditions in the engine. Unwanted reactions in the combustion chamber to carbon deposit build-up which is not good for your engine.

Carbon deposits on the valve, for example, will cause power leaks in the combustion chamber. The valves can no longer close properly with the presence of carbon deposits. Hence the maximum pressure in the cylinder cannot be achieved.

(Other cases of carbon deposit build-up in the cylinder can also cause increased compression ratios, but that is a topic for another day)

Q: What happens if you don’t change the engine oil?

A: As the lubricant loses its protective properties, the mechanical motions in the engine get more abrasive. This will damage the critical surfaces of the engine parts.

In summary, engine oil is crucial for the operation of your car. Like everything else, it has a service life. Scheduled oil changes keep your car reliable.