Can you mix two different brands of motor oil in your car if they both have the same viscosity (e.g. 0W-40)?
This is a question that we get asked from time to time by curious colleagues.
THE ANSWER IS NO!
Even if two different brands of oil have the same viscosity, you still should not be mixing them together.
(Why anyone would even consider doing this in the first place is something we cannot comprehend. But we digress.)
Technically, using a grade of oil that’s recommended by your car manufacturer is correct. However, if you combine two different brands of motor oil, you could be at risk of damage.
SO WHY CAN’T YOU COMBINE OILS?
The reason is that every brand of engine oil is formulated differently, especially with regard to the additives used by its manufacturer.
Nobody, possibly except for the top scientists and engineers working in these oil firms, knows the chemistry of their engine oils.
Therefore, we as consumers cannot be sure that one oil does not affect another one. We don’t know their chemistry.
As car owners, we should be kan cheong about this. Don’t do anything funny to your prized possession!
Who is to say that when two oils are combined, their additives won’t end up cancelling each other out? That leaves an engine with less protection.
WHAT IF YOU’RE SWITCHING BRANDS AT YOUR NEXT OIL CHANGE?
When the oil is drained, a thin film still covers those vital components in your motor.
It’s okay to then finish filling up with a different brand of engine oil. The new filling would now comprise the majority of the oil in your engine.
WHAT ABOUT MIXING MINERAL AND SYNTHETIC OILS?
That’s a big NO-NO.
Mineral and synthetic oils are totally different products. Trying to save money by using a bit of mineral oil then topping it off with synthetic oil is asking for trouble.
They must never be mixed together.