The only reason to choose 10W-30 is the price. 5W is a synthetic lubricant having better oxidation resistance and longer drain intervals. I am using 5W– 40 for my car instead of 15W– 40. It is a recommended lubricant along with 15W– 40 by the engine manufacturer, even though I am driving in a hot climate in the gulf region. According to API motor oil guide, you can use the 10w– 30 if the lowest expected outdoor temperature is above -18☌ and you are following the manufacturer’s recommendations. However, switching from 5W– 30 to economical 10W– 30 is not always recommended. (you must follow the manufacturer’s recommendations). 5W– 30 is thinner than 10W– 30 when cold. Conclusion:Īccording to API motor oil guide, If you are using 10W– 30, you can safely switch to 5W– 30 (in car engines). The only problem with 5W– 30 is NOACK (evaporation tendencies of a lubricant (engine oil) at high temperature). 5W– 30 oil has the same viscosity at 100☌ but is thinner when cool. Hence, the oil will not reach all around the moving parts of the engine when you turn the key. However, the problem with thicker oil is that the oil’s resistance to flow is high. The lubricant must reach all parts of the engine right away. We need the oil to be thinner at the time of starting the engine.

There is a problem with the thicker oil when the engine is cold. Most experts agree that 80% of engine wear occurs during startup (warming-up) the engine. In modern car engines, we need the oil to be thinner at the time of startup. The thickness of 10W-30 is much higher, as shown in the video demonstration. Air bubbles are trapped in the test tubes because of the low temperature. Both tubes with the steel ball were refrigerated at -18☌ for half an hour. Shown in the video are tubes with 5W-30 and 10W-30 lubricants. However, the 10W– 30 oil will be thicker (higher viscosity) than the 5W– 30 when it is cool. So both the oils 5W– 30 and 10W– 30 have exactly the same viscosity (SAE 30) when your engine is running, and will perform in the same way. Check the SAE Viscosity chart called SAE J300 standard. SAE 10 is thicker than SAE 5, and similarly, SAE 40 is thicker than or has a higher viscosity than SAE 30. A higher SAE number means that the oil is thicker or has a high viscosity. In the example above, 5W-30 has “ SAE 5” viscosity and 10W-30 has “ SAE 10” viscosity ( 5W and 10W) when cool. Windicates winter or cold and that’s why it is shown here in blue color. The number before “W” ( 5W-XX and 10W-XX) tells the SAE viscosity of the oil when it is cold. That is the operating temperature of an average engine. The number 30in both 5W- 30 and 10W- 30 indicates the SAE viscosity at 100☌ (212☏). At 100☌ (212☏), the viscosity or resistance to flow is almost the same for both 5W– 30 and 10W– 30. A steel ball moving from top to bottom indicates the thickness or viscosity of the oil.

Shown in the video are 5W– 30 and 10W– 30 engine oils in tubes at 100☌ (212☏).

Always follow the engine manufacturer’s recommendations. If you are living in an area where the outside temperature can go below zero It is better to use 5W– 30. As per API recommendations (1) for car engines, you can use 10W– 30 oil if the maximum expected outside temperature is above -18☌ (0☏). However, the 10W– 30 oil will be thicker when it is cold. That is usually 100☌ (212☏) when the engine is running (in an average engine). 5W– 30 and 10W– 30 lubricants have the same viscosity at the operating temperature of the engine.

Viscosity index verse viscosity number