Can You Mix 5w30 Motor Oil?

September 21, 2023

Your oil light comes on but you’re in a jam: you don’t have a spare litre in the trunk, and all the gas station has is a faded bottle of 5W30 conventional when what you need is 5W20. Do you run low or can you mix that old 5W30 motor oil with your synthetic oil? NAPA Canada is here to help.

Every motor oil manufacturer talks about their products’ special features. From conventional to full synthetic, whether it’s Castrol, Valvoline, or Pennzoil, every oil has a different blend of additives and specifications. Some are designed for performance, some are specifically made for high-mileage cars, and so on. There are also diesel-specific oils like Shell Rotella and auto manufacturer specifications such as GM’s Dexos. It’s tough for even the experts to keep track.

Automaker-Specific and Different-Viscosity Oils

The good thing is that when it comes to motor oil, it is possible to mix them. Some oil is always better than not enough oil. Take it from Mobil 1, whose website states that “Mobil 1 is fully compatible with conventional motor oils, synthetic blend motor oils, and other synthetic motor oils, should it be necessary to mix them.”

Every other mainstream motor oil company says the same thing. Different oils are compatible because they meet most of the same SAE International and American Petroleum standards.

Manufacturer specifications usually include guidelines regarding emergency top-ups. GM, for example, warns that using non-Dexos motor oil could result in engine damage not covered by warranty. But flip open a Chevrolet vehicle owner’s manual and it’ll say that “you may substitute oil displaying the API starburst symbol” when you have no choice.

Mobil 1 Motor Oil 5W30 Full Synthetic 5 Qt

53.00 $

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Castrol GTX MAGNATEC Motor Oil 5W30 Full Synthetic 5 L

50.49 $

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If you’re adding a litre of oil that’s the same viscosity, such as adding 5W40 to a car filled with 5W40, then you don’t really need to do anything until your next oil change. A one-time oil top-up with a different oil isn’t a problem. If your vehicle is using multiple litres of oil between changes, though, you should bring it to a NAPA AUTOPRO service centre to find the leak or diagnose the oil consumption issue. You should also be sure to use the right oil for all future top-ups.

If you have to add oil that is a different viscosity, then it’s a good idea to move up your next oil change. Changing the viscosity has a big effect on oil pressure in your engine and internal friction. The bigger the difference between your two oils, the more significant that effect will be. Doing a full oil change the next time it’s convenient will help protect your vehicle’s engine life and performance.

What about Mixing Conventional with Synthetic Oil?

What about using conventional oil instead of synthetic? Aside from some very high-performance applications, most vehicles do not specify whether you need conventional, synthetic, or a blend. So, if you need to add conventional to a synthetic fill, don’t worry about it. The motor oils will blend in your engine. Yes, you’ll lose out on some of the performance benefits of a synthetic oil, but that’s better than running your car or truck without oil.

Ultimately, the answer to the question “Can I use this oil?” is yes. In nearly all cases, you can use whatever motor oil is available as long as it’s clean and from a sealed container. Mixing oils is virtually always better than running on low oil. If you find that you’re having to top up your oil more frequently than usual, visit your local NAPA AUTOPRO specialist to find out where that oil is going.