Will your engine go KABOOM if you mix different engine oils from the same brand?

One day, a friend of mine asked me this completely random question, "Will I destroy my engine if I mix engine oils in my car?"

It never occured to me that this is actually a really valid question, because I've never done it before myself. However, in a less-than-ideal world, you might find your engine running low on oil, in need of a top up, and unable to procure the oil you're currently using.

So, what really happens when you mix engine oils from different brands, or mix different viscosities of engine oils in your engine? Will it go kaboom?

Different grades of viscosities? I'm confused

Don't be. Viscosity just simply means how well the engine oil will flow in specific temperatures. If you're unsure of what oil grade viscosity to use for your car, simply just refer to the owner's manual. 

Still confused about engine oil grades and viscosities? Fret not, here's some more help in understanding this topic in the video below.  Right now, let's focus on the burning question. 

Also read: Are you using the WRONG engine oil for your car?

Can I mix different grades of engine oil from the same brand?

So, the golden question is this: Is it okay to mix different grades of engine oil? Assuming both are from the same brand, but one is a fully-synthetic 5W-30, and the other a semi-synthetic 10W-40. Will mixing said oils grenade your engine? Short answer, no. 

In the short term, it's okay to mix oil especially if your engine is running low on oil. Any oil in the engine is better than no oil at all. So, if you're in a pickle where you need to top up your engine oil, go ahead. Just remember to change out this 'concoction' the first chance you get.

Why? As mentioned earlier, every car has different requirements in terms of engine oil grades. Sure, you won't suffer a catastrophic engine failure by mixing different engine oil grades. 

However, your engine's performance and efficiency will not be at it's intended optimum level, as opposed to running 100% of the recommended oil grade, as per your owner's manual. 

Can I then mix engine oils from different brands?

With regards to different brands of engine oils but with the same viscosity, sure you can mix them. But again, why would anyone do that outside of an emergency?

I'd wager that nobody consciously sends their car in for an oil change, and requests the service technician to mix different brands of engine oils. Well, in any case, there is a reason why.

It goes without saying that each brand has their own proprietary blend of additives in the engine oils they offer. Brands like Shell and Petronas spend massive amounts of their budget getting the right mix (yeah, I meant that) of additives in their products, only for a regular Joe to ruin it?

I maintain, mixing different brands of engine oils won't necessarily cause any harm to your engine. At most, you're just not getting the best engine performance from mixing because the additives in each respective oil was optimised to be used on its own. 

Therefore, the takeout here is similar to mixing oils of different grades: It's fine if you absolutely have no options (some oil is better than no oil in the engine, remember), but we don't recommend it if you have a choice.

Conclusion

If there's anything I've learned in my time owning cars with internal combustion engines, it is this: always carry at least a one-litre bottle of spare engine oil (the one your engine is running on, obviously) with you in your car's trunk. It's small and doesn't take up much space.

This practice will help you avoid the unwanted anxiety of running low on engine oil, especially if you're stranded in a remote place and unable to even purchase any spare oil. Better still, you save yourself from having to mix engine oils of different grades/brands.

If you make it to your next service interval with your spare oil still unused, feel free to use it for the next oil change, and then store another fresh one-litre reserve in the trunk. Trust me, it's helped me countless times.