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Motor Oil: Classification, Problems, FAQs

Motor oil is our most requested vehicle component, and the most used, after fuel. But although we use the car’s oil every minute, we find it everywhere and companies advertise aggressively in all media, it is arguably the least known “ingredient” of our car. The more is it known and used, the more we take it for granted and we are not interested about its past. Motor oil is even one of the great mysteries of drivers ready to be revealed in detail. If you are interested in everything about your car’s engine oil, how many types there are, what it’s made of and what problems or benefits can bring, read on.

What is motor oil and what does it do?

An oil called lubricant specially made to lubricate the moving parts of a combustion engine. The main job of the oil is to ease the friction between metal parts, but also to clean the motor, to contribute to isolation, to combat rust and cool the engine. Even if cooling is largely solved by the classical format of the pump, hoses and radiator, about 25% of the engine heat is removed by the oil inside, leading the heat away from metal parts that are in continuous motion and friction.

Oils today are made such as to evenly cover the internal parts and to isolate them from having contact with the air to protect them from rust. In addition, the oil has a special detergent to help clean up the component routes and remove metal scrap. This is where the oil filter that retains all the particles that the oil collects interferes.

This motor oil has to reach all the important components that move, being simply thrown on top of a propeller by the oil pump that collects the lubricant at the bottom.

How is the oil numbered?

We’ve all seen and bought oil for our car. But we only know that our engine needs the 5W-30 oil, for example. But what does it mean?

The Society of Automotive Engineers (SAE) is the one which implemented today’s naming and numbering. Therefore we notice that viscosity is mentioned as SAE 5W-30, for example.

The SAE index ranges from 0, 5, 10, 15, 20, 25, 30, 40, 50 to 60 in the prefix of the name. The second part of the name consists of the numbers 0, 5, 10, 15 and 25 with or without the letter W.

What many people did not know for sure is that W stands for winter. If the letter W is included in the name, it means that name refers to the viscosity in winter conditions. It is also called the cold engine start index.

In general, viscosity is measured as follows: the oil is allowed to penetrate through a standard orifice at some well controlled and constant temperatures. As the oil is thicker and flows heavier, the SAE will be higher. For example, a thin oil will have an index of 0, 5 or 10, whereas one for competitions, thick, specially made to work the high temperature will be 60.

The oil can be classified by two criteria: composition and viscosity.

Depending on the component, motor oil can be of 3 types: mineral, synthetic and semi-synthetic.

1. Mineral oil is an oil based entirely on alkali substances extracted from petrol, which is actually a kind of crude oil distillated under certain conditions. This kind of oil is the cheapest on the market because for its manufacture there are not so many ingredients used and the specifications on the packaging do not last in time.

2. Synthetic oil is an oil made entirely in the laboratory through synthesized chemical substances only. This oil is more expensive because it manages through various formulas to have a longer lifespan and adapt according to each motor and temperature. Motul was the first company that came on the car market with a full-synthetic oil called Century 300V in 1971.

3. The semi-synthetic oil is an average oil as price, made from a mixture of mineral oil with no more than 30% synthetic oil. Motul is the first company to offer such an oil in 1966, called Century 2100.

If we follow the viscosity, the motor oil is classified in two types: single-grade and multi-grade. In translation, we can say it’s the oils compatible with a small temperature range or a wide temperature range in which it can operate.

1. Single-grade oil is a rare oil because it is used in specific applications where it is known that that motor operates at a single temperature. For example, a car in Africa will only need oil for the warm season, while a car in Alaska will only use cold oil. Single grade oil has 11 viscosity index: 0W, 5W, 10W, 15W, 20W, 25W, 20, 30, 40, 50, and 60. The W ones are for the cold season. The lower the number, the lower the temperature at which it can work.

2. The multi-grade oil is what you most likely use. It is an oil for engines throughout a year they go through several seasons, and therefore through temperatures between -30 degrees to over 100 degrees Celsius.

Unlike single-grade oil, this one has some additives added that allow the lubricant to have a low viscosity at high temperatures and high viscosity at low temperatures. It is also called the all-season oil.

Diesel oil vs. Gasoline Engine Oil

On the market there are different oils for gasoline or diesel engines. The differentiation is recent because until now were universal lubricants. And there are different oils for each engine is operating at different temperatures.
For example, a gasoline engine can reach a maximum temperature in the upper part of the piston of about 160 degrees Celsius. While for diesel engine in the same place the temperature reaches double or more even 315 degrees.

The producers succeeded, through different combinations, to make specific oils for each fuel type separately. But the rule is the same: an oil with a higher viscosity index will perform better at higher temperatures.

Why do we really need to change the oil more often?

If we consider the reputation of the oil companies and the owners’ opinions posted on the Internet, we realize that, without a doubt, the more expensive is the oil, the better. I refer here to a prolonged lifetime in optimal conditions. If a Castrol can hold out without changing its viscosity, a no-name oil will lose its features and can become too liquid or gelatinous.

But the only way to verify the life span of the oil is either through personal experience or simply by avoiding unpleasant situations. Precisely for this reason there are distances at which you that must check the engine, regular changes every 10,000 or 15,000 miles, depending on the manufacturer.

If you overlook these important revisions, you risk, even if you have an expensive motor oil, to have problems. Whether you lose little by little as it is normal for cars that consume oil or it turns into thin liquid that no longer covers the internal parts with a protective layer, or it is solid and does not circulate through the engine. Even with a expensive, quality oil, if we go over the period suggested by the car service, we risk a lot.

Extreme and optimal situations

Yes, there are cases of cars that went almost 100,000 miles on the same oil from the factory. But only pure luck made
it possible for those cars to not get wedged engines, because after this distance the oil turns into grease and it is not effective.

So, if you care about your car or want to live under the impression that you can save some money by rarely changing the oil, yes, you can do that, but with the necessary risks.

In the best case scenario, however, it is good to take care of your engine at intervals even lower than what the manufacturer recommends. An optimum oil change is every 10,000 miles, along with the oil filter. Foam on oil cap is the first sign that you’re late with the oil change.


If you did not know what the numbering on the oil bottles bought at the store meant, you surely know now. And if you’ve ever thought that you car revision is not important and that changing the oil at regular intervals is not worth your attention, you were wrong. An oil change does not cost much so we should not play it safe and should do it every 10,000 miles.

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