OIL IS THE lifeblood of your vehicle. It keeps the car cool and stops friction and wear and tear on essential and expensive parts of the engine. Using the correct oil will prolong the life of the engine and can improve fuel economy.
So, to help you choose the right oil for your vehicle we’ve deciphered those cryptic tech specs on the bottles.
Oil Type
Mineral oil: this oil comes from processed crude oil.
Synthetic oil: this oil contains no mineral oil and is usually the most expensive as it works over a wide range of temperatures and conditions.
Semi-synthetic oil: this oil is a mixture of synthetic oil and mineral oil. Engines requiring this oil cannot use mineral oil but may benefit from upgrading to synthetic oil.
American Petroleum Institute (API) Service Classification
The API’S certification mark and service symbol identify quality motor oils for petrol and diesel powered vehicles. Oils with these symbols meet the API’s service standards. The first ever API category was SA, the next SB, then SC and so on. All API categories up to and including SH are now obsolete. The current categories are; SJ, for 2001 and older engines; SL, for 2004 and older engines; SM, for 2010 and older engines; and SN, for 2011 and older engines. For diesel engines, CH-4, CI-4 and CJ-4 are the current categories.
European Automobile Manufacturers’ Association (ACEA) Sequence
This is the European equivalent of the API rating. These ratings consist of a letter indicating the class of oil: A/B or passenger car compatible motor oils, C for catalyst compatible motor oils and E for heavy duty diesel engine oils. The classes are divided into categories ranging from 1-9 and you can read them all here.
Society of Automotive Engineers (SAE) Viscosity Code
The viscosity grade of motor oil is determined by the SAE. There are mono and multigrade oils. Monograde motor oils are not very common anymore. Multigrade oils span a wide viscosity range and consist of two numbers on the label e.g. 10W-30. The ‘W’ stands for winter and the number in front of the W indicates how the oil will flow when cold. The lower the number the thinner the oil and the thinner the oil the easier it flows. 10W means the oil will have the viscosity characteristic of a 10-weight motor oil when cold.
The oil is measured at certain temperatures and graded depending on its temperature range:
0W grade oil will flow properly up to -30°C
5W up to -25°C
10W up to -20°C
15W up to -15°C
20W up to -10°C
25W up to -5°C
The number that follows the ‘W’ indicates the oil’s viscosity at operating temperature as measured at 100°C. Therefore, an oil with a 10W-30 grade means it is a 10-weight oil, which will not thin any further than a 30-weight oil would when hot. 10W-30 oil will flow like a 10-weight oil at -20°C and like a 30-weight oil at 100°C.
Now, pay attention, here comes the science bit. Multi-viscosity oils have polymers added to them to prevent the oil from thinning too much as it warms ups. When cold, the polymers are coiled up, which allows the oil to flow at the indicated viscosity. When warm, the polymers unwind and form long chains, which prevent the oil from thinning any further than the higher number indicates.
Multi-viscosity oils allow the engine to work at a variety of conditions and temperatures: at cooler temperatures the thinner the oil the quicker it will flow to the engine reducing the dry running time and thus the wear and tear on the engine and at higher temperatures, the oil will retain thickness to provide adequate lubrication and protection.
But the oil with the widest viscosity range may not always be the best and it is recommended that you use oils with the narrowest viscosity span for the temperatures in which the car is likely to operate.
Some manufacturers have their own grade of oils that have to be used in specific models. These oils usually have an SAE grade equivalent but you need to consult the car manual or the manufacturer’s website. Some oil bottles have the compatible cars listed on them.
As always, it is advised that you use the specific viscosity grade, API rating or ACEA sequence oil as recommended by your manufacturer. By using the correct manufacturer recommended oil you will also stay within the terms of any warranty you may have.
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