Let’s clear one of the most common doubts among drivers: can you safely mix synthetic and conventional motor oil, and what really happens if you do? Understanding the effects can help you make smarter maintenance decisions and protect your engine.

Can you mix synthetic and conventional motor oil in your car?

Yes, but… in general, it’s safe to mix synthetic and conventional oils. They are chemically compatible, so topping up with a different type in an emergency won’t immediately harm your engine. From conventional to synthetic and blends in between, explore the different motor oil types and find out which one suits your vehicle best.

What happens if you mix conventional and synthetic motor oil?

Mixing is chemically safe, but it dilutes the unique properties of the synthetic oil. The advanced additives and thermal stability in synthetic oils become less effective when combined with conventional oil. Many “synthetic blends” are deliberately formulated mixtures, but a casual mix isn’t balanced. It’s functional as a temporary solution, but a full oil change should follow as soon as possible. Not sure if it’s time to change your oil? Our motor oil color chart helps you identify oil condition just by checking its color and consistency.

Can you mix 5W-30 and 10W-30 synthetic oils?

Mixing oils of similar viscosities like 5W-30 and 10W-30 results in a performance midway between the two: not as fluid in cold temperatures as 5W-30, and not as thick as 10W-30. It’s not dangerous, but it slightly alters performance, especially in very cold climates. If you need to top up, using high-quality oils like Ultra1Plus™ synthetic motor oils ensures better protection and stability. This should be done only when necessary, not as a standard practice. Before your next oil change, find out how much motor oil you need based on your engine size and manufacturer recommendations.

What happens if you mix two types of oil in an engine?

Modern oils are designed to meet API and ILSAC compatibility standards, so mixing types, synthetic with synthetic, synthetic with blend, or blend with conventional, won’t cause harmful chemical reactions. However, different brands or formulations may have varying additive packages (detergents, dispersants, antioxidants), slightly affecting oil effectiveness without directly damaging the engine. If you’re looking for reliable performance and protection without breaking the bank, check out our guide on the best conventional motor oil to keep your engine running smoothly.

Can you use synthetic oil in an engine specified for conventional oil?

Yes! A common misconception is that engines designed for conventional oil cannot use synthetics. As long as the synthetic oil meets the manufacturer’s recommended API and SAE specifications, it is fully compatible and often provides better thermal stability and engine protection. Curious about how long motor oil lasts before it needs replacement? We break down the factors that determine oil longevity and effectiveness.