Which Oil Should I Use? (Engine Oil Viscosity Explained)
If you go to an auto parts store, you’ll notice entire shelves filled with motor oil. Buying motor oil can be an intimidating experience if you’ve never bought motor oil before, but choosing the right oil is actually surprisingly easy. Here’s everything you need to know to choose the right type of engine oil.
What Does Oil Do? An internal combustion engine is made up of hundreds of precisely machined parts to close tolerances that operate at very high speeds. Motor oil reduces friction between these parts by forming a thin separating film.
This prevents metal-to-metal contact that would cause extreme heat and wear. Without oil, an engine would only run for a few minutes.
What is oil viscosity? Oil viscosity is the thickness of the oil at a particular temperature. The thicker the oil, the more resistance it has to flow. Also, thicker oils tend to stick to metal parts a little better, especially at high temperatures.
When engine oil heats up, it thins out and flows better, which is actually a good thing. Motors are designed to operate at approximately 88-100 degrees Celsius (190-212 degrees Fahrenheit). At this temperature, the oil will be much thinner than it would be on a cold winter’s day with the engine shut off.
Oil Viscosity Explained
The Society of Automotive Engineers (SAE) is the organization that creates technical standards for the automotive industry. These standards include a rating system that accurately measures and rates the viscosity of different engine oils. Engine oil is rated SAE J300.
When looking for engine oil, you’ll notice there are two numbers on the oil’s viscosity (for example, 5W-30, also written as 5W30). The first number is the oil’s viscosity at room temperature (also called cold). The number on the right is the oil’s viscosity at operating temperature.
When you first start your car, 5W-30 oil will behave similarly to SAE 5 oil. Once the car is fully warmed up, the same engine oil will behave like SAE 30. Various additives make the oil behave like a thinner oil at lower temperatures and like a thicker oil at higher temperatures.
As oil production technology has improved, the gap between these two values ​​has widened. For example, SAE 0 and SAE 50 are extreme differences in viscosity, but there is also 0W-50 oil. These oils are usually fully synthetic.
Which oil should I use?
This is a very common question, and the answer is very simple: use the oil recommended by your vehicle manufacturer. In rare cases, you may want to use a different weight oil, but generally the manufacturer knows best. Consult your owner’s manual for the recommended oil viscosity. In some cases, you can also check the viscosity on the oil cap itself.
In addition to the oil’s viscosity, look for other performance standards or certifications required by the manufacturer. For example, many vehicles require API certification or ILSAC requirements.
API stands for American Petroleum Institute.
ILSAC is the International Lubricant Standards Advisory Committee. The ILSAC standard is backward compatible with older standards. This means that you can use ILSAC GF-6 oil instead of ILSAC GF-5 even if your vehicle requires ILSAC GF-5. When you buy oil, you will find these standards on the bottle.
What happens if I use the wrong oil in my car?
It depends on the model of your car and what oil you use. Using 0w20 instead of 5w30 can thin the oil and accelerate engine wear. You usually don’t notice the accelerated wear until you’ve driven several thousand miles, and even then, you may only notice it through a Used Oil Analysis (UOA).
Using a slightly thicker oil than necessary usually doesn’t do anything bad. If you plan on driving your car on the track or racing, a slightly thicker oil is often a better choice. Thicker oil may quiet down older engines that are already showing noticeable wear.
Making the oil too thick will sacrifice fuel economy because it’s harder to pump the oil. Plus, your car may have trouble starting. Thick oil can increase oil pressure, which can cause premature oil pump failure. Modern engines are designed with tighter tolerances. This allows for the use of thinner oils, ensuring lower fuel consumption without any drawbacks.
If you use a very thick oil, such as 20W-50, in a modern engine, this oil may not flow fast enough to fill the small gaps between the rotating assemblies and the engine block. This leads to accelerated wear, just like using an oil that is too thin.
Conclusion
There are many different brands and qualities of oil to choose from. However, choosing the right oil doesn’t have to be complicated. The engineers who designed your engine know best, and as long as you follow their oil recommendations you shouldn’t have any issues.
