Tips from Used Car Advisor

Car Advisor Tamotsu Todoroki

Hi, this is Tamotsu Todoroki. I am a car advisor of
I write an online column every week to take care of your vehicle. My column is all about something useful and practical for your vehicle. Please have a look once to keep your car in good condition.


Everything You Should Know About Engine Oil Viscosity and Its Grades - Vol.412

Good engine oil is very important for your car's overall health. It lubricates the components of internal combustion engines, keeps them cool while the car is running, and protects from corrosion. Choosing the right oil for your car will mostly depend on the viscosity grade. In order to help you understand what this means, we'll explain what viscosity is, and how to find oil that's suitable for your car.

What is Oil Viscosity?
Engine oil viscosity determines how easily the oil pours in different temperatures. Oils with lower viscosity are thinner, and therefore pour more easily when the temperature is low. This is important because the oil shouldn't be too thick in low temperatures, since this prevents it from flowing to different part of your engine. Also, since a part of the crankshaft is submerged in oil, thick oil can prevent the engine from turning it properly.

This doesn't mean that oil should be as thin as possible. It still needs to be thick enough to ensure proper lubrication of the moving parts of the engine. The right viscosity will depend on the oil type, since different oils have different properties. The main types of oil are:
- Premium Conventional Oil - This is the most common oil type, which comes in different viscosities.
- Full Synthetic Oil - Mostly used in high-tech engines, synthetic oils are made to provide great flow at low temperatures, as well as high lubricity level at high temperatures.
- Synthetic Blend Oil - A mixture of synthetic and organic oil, synthetic blends offer great protection at high temperatures.
- Higher Mileage Oil - Formulated for high-mileage vehicles, these oils ensure the engine lifespan is long. They usually have higher viscosities.

Oil Viscosity Grades
Oils can be single-graded or multi-graded. Since the oil viscosity changes significantly according to temperature, multi-graded oils are the most common, since they are better at adapting to different conditions. Single-graded oils are very rare today, and can only be found in old vehicles, or engines found in lawnmowers or chain saws.

Viscosity grades are represented in the 'XXW-XX' format, where 'X' is a specific number, and 'W' stands for winter. The number before 'W' represents the oil's flow at 0° F (-17.8° C). The lower this number is, the less the oil thickens in low temperatures. If you live or mostly use your car in cold climates, where the oil tends to thicken faster, the recommended viscosity would be 0W or 5W.

The second number show the oil's viscosity at 212° F (100° C). It determines how resistant the oil is to thinning at high temperatures. If this number is higher, the oil will thin out more slowly.

The most important part of finding the oil with the right viscosity is taking into account the climate of the location where the car is used. The car will start a lot easier in the cold weather if the oil isn't prone to thickening. On the other hand, oil that doesn't get thin easily will let the car perform better in hot weather.

Viscosity Index
Another important thing to have in mind is the viscosity index (VI). VI determines the oil's resistance to temperature changes. The higher the oil's VI, the less its viscosity will be affected when the temperature changes. The main benefits of oils with high VI are:
- Lower fuel consumption and improved starting at low temperatures
- Lower oil consumption in hot weather

So as you can see, finding the right engine oil takes some research. If you want to avoid damaging your engine, or endangering the overall health of your car, make sure to take into account all of the factors mentioned in this article. Your safest bet would be to look for an oil that your manufacturer's guide recommends. If you still have some issues with finding the right oil, you can always seek help from a mechanic.