The main differences of synthetic and mineral oil explained simply:
- Mineral oil is produced by refining crude oil. Ideally, the manufacturer is able to get rid of the impurities and only keeps the homogeneous molecules.
- Synthetic oil is chemically manufactured. The producer “builds” molecular chains that possess the desired properties.
To visualize this process, just picture a pile of LEGO® bricks. If you want to produce synthetic oil, you are allowed to choose whatever piece of LEGO® you want, to build the exact form that you need. However, once you want to manufacture mineral oil, somebody already put some of the pieces together and you have to make do with selecting the pieces that fit best. You can still dismember some of them, but you will never have the full range.
Synthetic oil is build with the components that fit perfectly (left). When producing mineral oil, the manufacturer has to work with the available material (right).
- Mineral oil is cheaper than synthetic oil, as the production costs for mineral oil are lower.
- True synthetic oils have better flow properties even at low temperatures in wintertime. When cold starting your vehicle, your motor will be better supplied with motor oil, thus will be strained less.
- True synthetic oils are more temperature stable. That means, that the oil will keep its high viscosity, ensuring proper lubrication even under extreme conditions (high revs, full weight).
- To obtain similar temperature stability and flow properties in mineral oil, it is necessary to join additives to the oil. However, their effects can abate over time.
Synthetic motor oils perform better than mineral oils, but they are also more expensive.
Semi Synthetic Oils & Fully Synthetic Oils
Oil manufacturers often take advantage of the fact that buyers are willing to pay more once they spot the word “synthetic” as they, with good reason, expect higher quality. Thus, the term “synthetic” is widely used in advertisements, leaving the customer with a gallimaufry of formulations such as “HC-synthetic”, “Synt”, “SHC-synthetic”, etc.
The Problem: Confusing Names aka “Marketing”
The words “synthesis” and “synthetic” are not protected terms. The two manufacturers Mobil (now ExxonMobil) and Castrol even fought in court over the use of the terms. Mobil hold the opinion that Castrol had no right to name its brand Syntec a synthetic oil. Though the oil was strongly refined and chemically changed, it was still a mineral oil and not a fully synthetic oil. Eventually Castrol was allowed to retain the name, and since then, the term is used rather “creative” by many manufactures.
Plenty of motor oils, which consist of group III base oils (generally hydrocracked mineral oils) are therefore called synthetic or semi synthetic. Those oils are either strongly refined and/or consist partly of fully synthetic oils of group IV base oils (PAOs).
However, the term “fully synthetic” can provide some certainty, as fully synthetic motor oils are supposed to consist of at least 80% of group IV base oils (PAOs). Their viscosity is typically SAE 0W-30 and 5W-40.
Final Comment On Engine Oils:
When checking out the market for motor oil, it is easy to get the impression that many manufacturers generally don’t wish to label their products correctly, be it fully synthetic or semi synthetic. The outer packing often only titles “synthesis”. Is the good reputation of fully synthetic oils supposed to rub off on other products (that not necessarily have to be bad quality)?
Besides, some products or product line-ups that were previously based on fully synthetic base oils are changed to base III oils without much fuss, but while retaining the brand name. It does seem like there is some transparency missing here…