Motor oil: mineral, synthetic or fully synthetic?

July 2020 – Motor oil has developed from a simple lubricant to a high-tech liquid. At the same time, the number of oil grades and specifications has increased significantly. Oliver Kuhn, deputy head of the oil laboratory at LIQUI MOLY, provides more insight and explains what really matters.

What kind of oils are there?

Oliver Kuhn: Motor oils can be roughly divided into two categories: mineral-based and synthetic oils. Mineral oils are becoming less and less important for cars because they do not offer such high performance. Modern engines demand much more from the oil than old engines. Only synthetic oils can meet these requirements.

So synthetic oils are the better oils?

Oliver Kuhn: Yes, but you can also mix a mineral oil with a synthetic oil. However, such semi-synthetic oils are playing an increasingly smaller role in the market, because their performance is not high enough, due to their mineral content.

Sounds complicated. But then, at least, all synthetic oils are similar?

Oliver Kuhn: Unfortunately, no. There are two different ways in which synthetic oils can be produced. By one of these methods, a so-called PAO oil is obtained at the end. This is the classic synthetic oil as it came on the market in the 1970s. It is chemically very pure and therefore very effective, but also very expensive to produce. With the other approach, the oil is produced by hydro-cracking, which is why these oils are also called HC oils in technical jargon. HC oils are more modern and came up in the 1990s. Today, they offer the best possible performance for all modern engines.

Should I rather use a PAO oil or an HC oil?

Oliver Kuhn: This choice is often not even available. Almost all oil development nowadays takes place on the basis of HC oils. Many oil specifications can only be met with HC oils.

How can I tell what kind of synthetic oil it is?

Oliver Kuhn: That is not so easy, because there are no uniform terms here. In the USA, for example, both PAO oils and HC oils can be described as fully synthetic, but in Germany only PAO oils may be called synthetic. That is why we give our HC oils the label “Synthesis Technology”. Other oil manufacturers use terms such as “100% synthetic” or “synthetic mix”, where it is not clear what exactly is meant.

That is quite confusing.

Oliver Kuhn: True. But the question of which synthetic oil is actually meant in a particular case is of no importance to drivers and workshops. It is not about which oil is supposedly better. The decisive factor is that the oil meets the specifications which the car manufacturer has set for that model. This is given in the manual of the car, or you can use our free Oil Guide at www.liqui-moly.com.

So if the specification is right, it doesn’t matter whether it’s a PAO oil or an HC oil?

Oliver Kuhn: Correct. In any case, the additive packages are becoming increasingly important. Today, they are the most important component of a motor oil besides the actual oil. They provide a large part of the motor oil’s performance. With some very modern motor oils, the base oil is hardly more than just the carrier fluid for the additive packages.

So why are there always discussions about which synthetic oil is the better one?

Oliver Kuhn: This is an echo from the past. When the first HC oils appeared 30 years ago, the quality difference to PAO oils was even greater. But that was a long time ago. No expert would have such a discussion today.