Can You Mix Engine Oil?

Reviewed June 2026 by GarageDex editorial

GarageDex's oil guide gives a reassuring answer: you can mix different brands of engine oil, and you can mix synthetic with conventional, because oils licensed to the same industry standards are designed to be compatible. You can also top up with a different grade in an emergency. Running the engine low on oil does far more harm than mixing ever will.

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Mixing brands: fine

Oil brands formulate their own additive packages, but oils licensed to the same industry standard are tested to be compatible with each other. Look for the licensing mark on the bottle, and match the grade and any manufacturer approval your engine requires.

Synthetic with conventional: fine

Mixing the two gives you, in effect, a synthetic blend. It does not harm the engine, but it dilutes the longer life and stronger temperature protection of full synthetic. If your engine requires full synthetic, top up with full synthetic when you can. See synthetic vs conventional oil.

Different grades: fine in a pinch

Adding a quart of a different grade to reach the full mark shifts the viscosity a little. It is a reasonable short-term fix. It is not something to do for a whole oil change on an engine that specifies a particular grade. The difference between grades is explained in 5W-30 vs 5W-20 vs 0W-20.

What to avoid

Oils without a current licensing mark, which are not certified against modern engine standards.
Motorcycle, two-stroke, or diesel-only oils in a car engine unless the specification allows them.
Aftermarket oil additives on top of a modern licensed oil, which is already formulated as a complete package.

Top up correctly

Check the level with the engine off and on level ground, add a little at a time, and stop at the full mark. Then look up your car's verified oil grade and capacity so the next full change uses the right oil.

Frequently asked

Can I mix synthetic and conventional oil?

Yes. They are compatible, and the result is effectively a synthetic blend. You lose some of the full synthetic's benefits, but it will not damage the engine.

Can I mix two different brands of oil?

Yes. Oils that meet the same licensed standard, such as API SP, are formulated to mix safely. Stick to the grade and specification your engine needs.

What happens if I top up 0W-20 with 5W-30?

A small top-up changes the overall viscosity only slightly and is unlikely to cause harm for the short term. Return to the specified grade at the next oil change.

Is it better to top up with the wrong oil or drive low?

Top up. Low oil is a genuine risk to the engine, while a different compatible oil in small amounts is not. Correct it at the next change.

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