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Difference Between 10w30 and 5w30 Motor Oil

Satyajeet Vispute
Many of us don't know what the writing on the label of a bottle of motor oil means. Strange terms such as 10w30 or 5w30, that are commonly found inscribed on them, seem most confusing. In this story, we shall explain the meaning of these two terms, and also highlight the differences between them.


The viscosity of motor oil is graded by measuring the time taken by a standard amount of oil to flow through a standard pipe at a standard temperature.
If you look inside an engine from the point of view of a layman, what you'll see would be something similar to the scene in a battlefield! The atmosphere inside is torn by tremendous explosions and the deafening clash and clamor of metal slamming on metal.
In the midst of all this chaos, one is left wondering what exactly it is that prevents a complete engine breakdown. Well, the answer lies in lubrication.

An engine lubricator, popularly known as motor oil, is the guardian that protects the engine by preventing any one of its many moving parts from destroying each other.
There are many different types of motor oils manufactured for several specific applications. For car and bike owners, 10w30 and 5w30 are the two most significant types. But what is the difference between them? For us to understand that, we will first have to understand what motor oil is, and how it is graded.

Motor Oil

Motor oils are specially manufactured lubricants that are used in internal combustion engines. Traditionally, they are derived from petroleum by-products. However, nowadays, synthetic and semi-synthetic motor oils are widely used, which are a blend of base oils comprising hydrocarbons, polyalphaolefins (PAO), and polyinternalolefins (PIO).
The main function of motor oil is to reduce friction. Within an engine, there are several small and large parts that move against each, other resulting in heat generation, which is a non-beneficial conversion of the kinetic energy generated by the engine.
Also, if this is allowed to go on, the constant wear and tear will wear out the parts in friction much sooner than expected. Motor oil coats these parts under friction and forms a barrier between them. This significantly reduces wear and tear.
Also, as the oil circulates through the engine, it absorbs the heat generated by the moving parts, effectively cooling them down.

Motor oils are extensively used in the engines of cars, trucks, bikes, lawnmowers, diesel generators, etc. However, each of these applications require a different kind of motor oil.
There are several different parameters used for classifying motor oils. One of the important ones is the oil's grade.

Grades and Multi-grades

The single most important physical parameter that determines a motor oil's suitability for a particular application is its viscosity. The viscosity of a liquid refers to its resistance to free flow.
For example, water being lighter and thinner, flows much more freely as compared to sugar syrup, which is both thicker and heavier. Thus, it can be said that sugar syrup has a higher viscosity than water.
For motor oil, higher viscosity means better padding against friction, and thus, improved performance. However, too much viscosity makes it difficult to pump the oil through the engine.
Hence, certain suitable viscosity ranges are agreed upon by the Society of Automotive Engineers (SAE) for different engine types and applications. As such, different motor oils are graded accordingly.

Now, oil viscosity varies depending on temperature. A less viscous oil tends to thicken in low temperatures, and vice versa.
So, until 1960, it was a common practice to use different grades of motor oils during winters and summers. In cold temperatures, low-grade oils, having lower viscosity, were used to allow for better circulation during a cold-start of the engine.
However, as the engine would heat, the oils would lose their viscosity and thin considerably beneath the recommended lower limit, resulting in increased engine wear and tear. To solve this issue, multi-grade oils were developed.
Multi-grade oils are synthetic oils containing polymers which expand with heat effectively, increasing the viscosity up to a certain set limit. These oils have a base viscosity level, which increases to the final viscosity level in proportion to the engine's heat.
Thus, during cold-starts in low temperature, these oils, owing to their low viscosity, are able to flow freely and quickly through the engine. After a few miles, when internal combustion raises the engine's temperature, the oil viscosity reaches the final higher level, allowing it to provide maximum protection to the engine.

5w30 and 10w30 Multi-grade Oils

Both 5w30 and 10w30 are multi-grade oils. Their nomenclature itself is enough to indicate this, provided that you know how to decode it. Let's take 10w30 as an example. It can be split into two sections - '10w' and '30'.
The 'w' in 10w stands for 'winter', while the number 10 represents the oil's base viscosity. In cold temperatures (winter), during engine cold-starts, this oil will have a viscosity of SAE 10, allowing it to flow freely through the engine.
After the engine has run for some time, the heat generated within it will push the viscosity till it reaches its upper ceiling, which is specified by the next section, that is, '30'. It represents the maximum attainable viscosity of this oil - SAE 30.
Similarly, in case of 5w30 motor oil, the base viscosity is SAE 5, which increases along with the engine's temperature up to a maximum of SAE 30.

10w30 Vs. 5w30: Comparison

5w30 is less viscous, that is, thinner in low temperatures as compared to 10w30. This allows it to be pumped much more easily through an engine. Hence, in colder regions, it is advisable to use 5w30 oil as opposed to 10w30. However, many older generation vehicles have engines with design limitations.
They require a little more wear-protection during cold-starts. In such cases, the thicker 10w30 has to be used, instead of 5w30.

Modern vehicle engines have better bearing clearances between their moving parts, so their manufacturers recommend the use of the thinner 5w30 oil for increased lubrication and better mileage.
But in most cases, 10w30 oil can still be used, although sticking to the manufacturer's specifications is always better.

Motor Oil for Lawnmowers

A question that many people ask is which of the two oil types is suitable for lawnmowers? Lawnmower engines have a higher RPM than automobile engines, and are required to work in rougher and dirtier conditions. Hence, they require constant and consistent lubrication using the manufacturer's recommended grade of oil.
Yet, unless the lawnmower's user manual specifies otherwise, in most conditions, 10w30 will work well. Only in really cold regions should one opt for the 5w30 oil, but before that, don't forget to ask yourself - who mows the lawn in such low temperatures anyway?
Thus, both 5w30 and 10w30 are important types of motor oils which are manufactured for use in different conditions. 10w30 is a kind of an all-round oil which will provide acceptable levels of protection to the engine in a wide range of temperatures.
However, 5w10 is now the recommended standard in most vehicle engines, and it is clearly the better option for very cold winters.