Oil is extremely important in any engine, it lubricates to prevent wear and heat. More cars now require a specific type of oil, in comparison to older vehicles that had less precise tolerances.  

It is even more important then, to ensure your car is getting the correct oil. In this article, we’ll cover the main types and explain their benefits.

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Mineral, semi-synthetic or synthetic? 

These are the main three types of oil. They refer to the composition and method of manufacture of the oil and affect their performance.  

Mineral 

Often identified purely by the lack of the words ‘synthetic’ or ‘semi-synthetic,’ these are the type of oils used before synthetic technologies took hold.  

They are made entirely from mined crude oil, which is refined and processed in a similar way to other oil products.  

Semi-synthetic 

In essence, these are a mixture of synthetic and traditional mineral oils. With the synthetic part has undergone complex and intricate processes to improve its performance.  

Synthetic oils are still often derived from crude oil but have a significant portion of additives and modifiers to improve performance. 

Fully Synthetic 

No amount of un-modified mineral oil is used to make synthetic oil. Although crude oil still forms the base for a lot of synthetic oils. Manufacturers don’t give away specific recipes, but the crude oil component is heavily ‘synthesised’, meaning it is chemically modified. 

In many circumstances, fully synthetic oil is the best-performing oil. In most brands, fully synthetic oil is the recommended type. 

Oil weights and viscosity 

Like all liquids, oil has viscosity, which is the degree to which a liquid resists movement. Treacle is an example of a liquid with a high viscosity, water has a fairly low viscosity and petrol is lower still. 

Viscosity is very important in engines and machinery. A moving system has specific design features to use certain types of lubrication, for example, a joint with slow and limited movement such as a suspension component would make use of seals and a very thick or viscous lubricant such as grease. 

A high-revving engine with very tight tolerances and need for heat dissipation needs a lubricant free-flowing enough to be pumped around effectively, but thick enough to provide adequate lubrication.  

Another key property of engine oil is that it needs to operate effectively at both cold and hot temperatures. This is important as car engines often go from completely cold to operating temperature multiple times in one day.  

The SAE system of oil designation allows the easy labelling of oil for both viscosity and temperature performance.  

Oil ratings explained 

Let's take an example, the oil required for a 2010 Volkswagen Golf TDI is 5w30. Let's break that down: 

• 5: This is the cold viscosity rating, chosen from a scale between 5 and 50. This car needs a rating of 5 
• W: This designates winter. This defines the standards at which the cold viscosity rating is taken, most oils use this standard for ease 
• 30: This is the viscosity when at operating temperature. 

So how does this compare against other oils? If we used 10w30 oil, the engine would suffer from excessively thick oil in cold conditions, but once up to temperature, the oil would be perfectly suited.  

In reality, the difference between the two would be indiscernible, but using the incorrect oil could cause undue strain on your engine, or cause the warranty to be invalidated.  

The best tip is to use the recommended oil as stated by your owner’s manual. 

SAP rating 

One other characteristic of engine oil is the SAP rating. This stands for Sulphated Ash & Phosphorus. 

In diesel-engined cars, a diesel particulate filter (DPF) is used in the exhaust system to reduce harmful emissions. These can become clogged with soot and other components of exhaust gas, including sulphated ash and phosphorus. 

Low SAP oils as the name suggests contains less of these elements than normal oils. Thus having a reduced effect on a diesel’s DPF. If your car is diesel, it will almost certainly require low SAP oil. There are some diesels that do not have a DPF, typically over 20-year-old ones. 

Manufacturer-Specific Oil 

Some manufacturers including BMW, Audi, Mercedes and more, have developed their own grading systems for oil, they often include designations for long life, heavy duty and more.  

If you are unsure of which specific oil your car should use, check your owner’s manual where the exact oil and how often it should be changed will be listed.

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