Fully synthetic, semi-synthetic or mineral oil: which does my car need?

Your car needs whichever oil meets the grade and specification in its handbook. For most modern cars, that is a fully synthetic oil. Semi-synthetic oils suit many older cars, and mineral oils are mainly for classic engines.

What is mineral oil?

Oil refined from crude oil, and the simplest kind of engine oil. It suits the engines designed for it, mainly classic and vintage cars, which often take thicker grades such as 20W-50. Duckhams Classic Q oils are mineral oils made for these engines.

What is semi-synthetic oil?

A blend of mineral and synthetic base oils. It copes with cold starts and heat better than a mineral oil, and usually costs less than a fully synthetic one. It suits many older petrol and diesel cars that take a grade such as 10W-40 or 15W-40, like Duckhams QS 10W-40 RMV and QS 15W-40 VMB.

What is fully synthetic oil?

Oil made from synthetic base oils, which are more uniform than refined mineral oil. It flows better from cold and holds up better at high temperatures, which is why the thin grades and longer service intervals of modern engines rely on it. Every Duckhams QXR oil is fully synthetic, and so are most QS oils.

Is fully synthetic oil better?

For an engine that asks for it, yes: nothing else will meet its specification. For any other engine, the right oil is still the one that meets the grade and specification in its handbook. A fully synthetic oil can replace a semi-synthetic one if it meets that same grade and specification. What you should never use is an oil that doesn't meet them, whatever it is made from.

How do I know which my car needs?

Look up the grade and specification in your handbook, or enter your registration in Find My Oil, which shows both and the Duckhams oils that meet them. The label on every bottle says whether the oil is fully synthetic, semi-synthetic or mineral.

Should I use synthetic oil in a classic car?

Usually not. Most classic engines were designed for mineral oil and run best on it, in the grade their manual gives. Our classic car oil guide explains why.

Questions

Can I switch from semi-synthetic to fully synthetic oil?

Yes, if the fully synthetic oil meets the grade and specification your handbook gives.

Can I mix synthetic and mineral oil?

They mix safely, but the blend loses some of the synthetic oil's benefits, so keep it to a small top-up. More in our guide to mixing engine oils.

Does fully synthetic oil last longer?

It resists breaking down for longer, which is what allows longer service intervals. Still change it when your car's schedule says: see how often to change your engine oil.