Can you mix 5-20 wt oil with 10-30 oil?

It is strongly advisable against mixing different types of oils, particularly when it comes to engine oils. Mixing oils of different viscosities, such as 5W-20 and 10W-30, can alter the overall viscosity and performance characteristics of the resulting mixture. This can have negative consequences for your vehicle's engine and may lead to issues like increased wear, reduced efficiency, and potential damage to engine components.

Here are some reasons why mixing different engine oils is generally not recommended:

a. Different Viscosity: The "W" in the oil grade stands for "winter," indicating the oil's cold-weather performance. The number before the "W" represents the oil's viscosity at low temperatures. In this case, 5W-20 oil has a lower viscosity at cold temperatures compared to 10W-30 oil. Mixing these oils changes the overall viscosity and may not provide the optimum level of protection for your engine across all operating conditions.

b. Additive Incompatibility: Engine oils contain various additives that are carefully formulated to perform specific functions, such as enhancing lubrication, reducing wear, preventing corrosion, and controlling deposits. Mixing different oils may lead to the interaction and dilution of these additives, potentially reducing their effectiveness or causing adverse chemical reactions.

c. Engine Wear and Performance: Using a mixture of oils with different viscosities and additive packages can compromise engine lubrication. It may not provide adequate protection against wear, especially during critical engine startup and high-temperature operation. This can accelerate engine wear and lead to reduced performance and durability.

d. Warranty Issues: Mixing different oils may void the warranty of your vehicle's engine. Refer to your vehicle's owner's manual or consult with your authorized dealer regarding the recommended engine oil type and specifications.

It is crucial to use the engine oil specified by your vehicle's manufacturer based on the climate, operating conditions, and engine specifications. If you have any doubts about which oil to use, it's best to consult with a qualified mechanic or automotive expert to avoid any potential risks to your vehicle's engine.