What will happen if I use 20W40 engine oil instead of 10W40?

 Using 20W40 engine oil instead of 10W40 can potentially have some effects on your engine's performance and lubrication, especially in terms of how the oil behaves under different temperature conditions. The numbers "10W40" and "20W40" represent the oil's viscosity rating, and they provide information about how the oil flows at different temperatures.

Here's what could happen if you use 20W40 oil instead of the recommended 10W40:

Cold Start Performance:

The "10W" or "20W" part of the viscosity rating indicates how the oil behaves at cold temperatures. The lower the number, the better the oil flows in cold conditions. 10W40 oil has a lower viscosity at cold temperatures compared to 20W40 oil. Using 20W40 instead of 10W40 might lead to poorer cold start performance, which can result in increased engine wear during startup, especially in colder climates.

Oil Flow at Operating Temperatures:

The "40" part of the viscosity rating indicates the oil's viscosity at higher temperatures. Both 10W40 and 20W40 have the same viscosity at higher temperatures, which is the typical operating temperature range of the engine. Therefore, the difference in viscosity at higher temperatures might not have a significant impact on engine performance.

Fuel Economy:

The higher viscosity of 20W40 oil at cold temperatures might result in slightly reduced fuel efficiency during cold starts compared to 10W40 oil. However, the effect on overall fuel economy during regular driving might be negligible.

Engine Wear:

While both oils have the same viscosity at higher temperatures, the use of 20W40 oil could potentially lead to slightly increased engine wear during cold starts due to the higher viscosity at low temperatures. Engine wear is more likely to occur when the oil is thicker and doesn't flow as easily during startup.

In summary, while using 20W40 oil instead of 10W40 oil might not lead to catastrophic damage, it could result in slightly compromised cold start performance and possibly slightly increased engine wear during startup.

It's generally a good idea to stick to the manufacturer's recommended oil viscosity for your vehicle to ensure optimal performance and engine longevity, especially if you live in an area with colder temperatures. Always consult your vehicle's owner's manual for the correct oil specifications.