Differences between 5w40 and 10w40 Motor Oils

Any mechanical moving part in a machine needs lubrication. Lubrication using oil helps in minimizing tear and wear brought about by friction. Additionally, lubrication also prevents corrosion of parts, cleans, and cools the machine through the transfer of heat (“Motor oils and engine lubrication”, 2016). This tells us how important oil is to a mechanical engineer.

Characteristics of 5W-40 Motor Oil

The 5W-40 motor oil

The 5W-40 Motor oil is thin motor oil that will enter the vehicle’s moving parts easily and lubricate when the machine tries to be started up. The number ‘40′ indicates that it is thicker than the average motor oil which is ‘30’ for man cars. The oil is known to lubricate the engine even when it is hot. This is contrary to other engine oils which when they become hot their efficiency of lubrication goes down.

Mechanics always prefer this engine oil because of its ability to support higher mileage engines. This is because this oil is thicker even when the operating temperature is high. It would offer excellent lubrication to moving parts better inside the motor that has been worn out because of the age or strain.

More specifically, this oil is used in high-mileage vehicles and in places that may experience winters of 5 degrees Celsius. This oil is effective for cold engines that need to be started but it may be ineffective in engines which are used in freezing climates.  

The 5w40 is synthetic motor oil with a viscosity of 5 in low temperatures and a viscosity of 40 at higher temperatures. Therefore, this oil is less viscous at high and low temperatures.

The viscosity of oil changes with temperature, therefore the 5w-40 motor oil was made to offer protection in a range of operating temperatures. This is the reason why the viscosity of the oil is made up of two numbers so that the user knows the operating temperature extremes of the oil. As have been described in this article, the first number followed by W describes the viscosity of the oil.

Using the correct oil is helpful to the motor engine. It makes the engine to run smoothly. Wrong oil will certainly damage the engine, burn more fuel, increase emissions, and can even make the warranty of the car to be invalid (Kobe, 2014). It is important to note that oil specifications determine the type of engine which particular oil should be used. The 5w-40 motor oil is clean, heat resistant, wear protection and strength. Although specifications need to be regularly updated to conform with the change in the technology of the engines, this motor oil still remains one of the latest specifications of advances in oil manufacture.

The 10W-40 Motor Oil

The 10W-40 motor oil is a bit thicker than 5W-40 oil but it is still thin and operates well under well to offer lubrication to the engine parts during the time of starting of the engine. The number ‘40′ marked on the oil means that it would be thicker than the average but still, it will withstand the heat produced by the running engine. At high temperatures, the 5W-40 is thinner and therefore 10W-40 would be more effective in operating at high temperatures. However, at extreme temperatures, the number may not depict the actual viscosities.

Generally, the 10W-40 motor oil offers excellent protection to the engine at higher temperatures than 5W-40 motor oil. At these extreme temperatures, the oil should be more viscous so that it does not turn to a thin liquid which may not offer effective lubrication during and after starting of the engine.

For the 10W-40, the first number (10) represents a temperature of 10 degrees Celsius while the ‘W’ stands for winter. It means that the oil should operate well at the start of the engine when the outside operating temperature is less than or at 10 degrees centigrade. However, the 10W-40 is not as reliable as the 5W-40 engine oil is as a start engine in winter and cold temperatures. This means that this type of oil is highly effective in situations where the surrounding temperatures are high. Because of its adequate thickness, it will offer excellent lubrication even when the temperatures are extreme. Taking into account that the thicker the oil, the higher the viscosity; the 10W-40 oil is, therefore, more vicious even when the temperature has risen to a certain value. 

In summary, the 10W-40 motor oil is more viscous; has a viscosity of 10 at low temperatures, and has a viscosity of 40 at high temperatures.

The 10W-40 motor oil is preferred by motorists using higher mileage vehicles because the oil is thicker while the engine is hot. This type of oil is applicable in the starting of motor vehicles in winter or cold climates that ma experience temperatures o up to 10 degrees Celsius. However, it is not as reliable as the 5W-40 oil, as this supports lower winter colder temperatures.  

Because of the viscosity grade, the 5W-40 serves as the best choice of motor oil for fuel economy. Most of these oils will offer 1-2 percent fuel saving. The lower viscosity fuel offered by 5W-40 motor oil makes it be fuel economy oil than most oils in the market. By using these lower viscosity oils in clean engine design, the economy of the fuel can be improved remarkably.

For older engines, it is advisable to keep using the 5W-40 oil rather than 10W-30 oil because of its low viscosity and also the old engines have worn out parts which require adequate lubrication. Therefore, it means for fuel economy there are many variables that need to be considering, for instance, if your vehicle has an old engine and the vehicle is operated under extreme temperatures, then you need 10W-30 engine oil because it is heavy even though the fuel economy is lowered.

The prices of these two engine oils (5W-40 and 10W-30) differ because of their performance. The 10W-30 engine oil as has been explained is heavy engine oil which offers excellent performance in cold climates. Therefore, in warm climates, it is advisable to choose the 10W-40 engine oil while it the 5W-40 engine oil offers excellent lubrication in cold climates because of its low viscosity. It means that the prices of each of the types of oil will differ depending on the prevailing weather condition.


Kobe, K. (2014). Motor oils and engine lubrication. Journal Of Chemical Education, 28(1), 54. doi: 10.1021/ed028p54.2

Motor oils and engine lubrication. (2016). Wear, 12(5), 381-382. doi: 10.1016/0043-1648(68)90545-0