Can I mix different engine oils?

Yes, if you need to. When the level is low, topping up with a different oil is far better than driving with too little. Engine oils are made to mix without harm. For the best protection, though, top up with an oil of the same grade and specification as the one already in the engine, and go back to the right oil at the next change.

Can I mix different brands of engine oil?

Yes, as long as both meet the grade and specification your car needs. Two 5W-30 oils to ACEA C3 from different brands will mix without any problem.

Can I mix 5W-30 and 5W-40?

To get you home, yes. The mix ends up somewhere between the two grades, which may not be what your engine is designed for, so top up with the grade in your handbook as soon as you can. If you have added a lot of the wrong grade, change the oil. More on grades in what the numbers on engine oil mean.

Can I mix synthetic and mineral oil?

Yes, they mix safely. The blend loses some of the benefits of the synthetic oil, so keep it to a small top-up.

When should I avoid mixing oils?

When your car needs a particular specification: a low-ash oil to protect a diesel particulate filter, for example, or a carmaker's own specification such as VW 504 00 or a Ford code. Topping up with an oil that doesn't meet it dilutes that protection. If you can, keep a litre of the right oil in the boot.

How much oil should I add?

A little at a time, about 200 ml, checking the dipstick as you go until the level is near the upper mark. Don't fill above it. Our guide to checking your engine oil level shows how. If you find yourself topping up often, have a garage check for a leak or for the engine burning oil.

Which oil should I top up with?

The one that meets your handbook's grade and specification. Find My Oil shows it from your registration, and Where to Buy shows where to get it.

Questions

Is it bad to mix engine oils?

Not as a top-up. It is far worse to run low on oil. Use the right oil when you can.

Do I need to change the oil after mixing?

Not after a small top-up of a suitable oil. After a large amount of a different grade, or of an oil that doesn't meet your car's specification, change it sooner rather than later.