Why Do Different Cars need Different Engine Oil?

We’ve all walked into the auto section of hardware shops or the petrol station kiosk and spent time looking blankly at the sheer array of possible engine oils to use. Your eyes turn inward at the kaleidoscope of colours and choice — but why does there even need to be so many different types of engine oil? We can understand the variety of products when it comes to things like cereal or children’s toys, but engines are pretty much all the same, aren’t they?

The answer, of course, is no — engines may perform the same function but they’re designed individually to meet the needs of individual cars. In order to do that job properly, they need engine oils with certain properties that may be counter-productive to other engines.

Let’s look at why.

Engine oil lubricates, but there’s a fine line

The main thing that engine oil does is, as you’re likely aware, lubricate the mechanical parts in an engine. Engines are made up from lots of relatively intricate moving metal parts and the main result of rubbing metal against metal is friction.

Friction’s the enemy of engines (in some respects it’s essential, but that’s another topic for another day) because friction causes parts of the engine to wear prematurely. So you don’t want the engine to wear prematurely, you ideally don’t want the engine to wear at all, but another significant factor in engine mechanics is heat.

Excessive friction causes heat, which makes parts expand and create more friction until you’re left with a puddle of what used to be metal. Engine oil, then, helps to reduce friction but also has the added benefit of dissipating heat from engine components.

Much like a coolant system runs the coolant around in order to take heat from one area and release it elsewhere, the oil in an engine moves the heat to places where it can dissipate safely.

The thermal capacity of the oil is therefore very important depending on the type of engine that it’s being used for.

What do the oil numbers mean?

While oil’s main job is to lubricate and cool, it also helps with things like cleaning the engine (through certain additives), helping to preserve seals from drying and becoming brittle, and also helping to stop corrosion & rust that might form if parts of the engine are left exposed to the air.

The two main components of engine oil are viscosity and thermal capacity — and these two things are really closely connected. Think about how much olive oil changes when you put it into a hot pan.

Let’s take a “Normal” oil for reasonably small engine cars: 5w30.

The two components here represent the winter and hot viscosity grades.

5w here means that, when cold, the oil has a viscosity rating of 5, and the 30 indicates that its viscosity rating rises to 30 when hot. Much like the oil in the pan, the ambient air temperature plays an important role for engine oil. If you’ve ever tried to pour extra virgin olive oil in the depths of winter, you’ll likely know what we mean!

An engine’s oil needs to be able to perform optimally at both extremes for your particular climate — and 5w30 oil is great for most UK uses because it’s quite broadly capable. Compared to, say, 10w30, a 5w30 oil is thinner at cold temperatures, which makes it more able to lubricate and dissipate heat.

Need engine oil?

If your engine’s overheating or you’ve noticed that the oil has become too dark and thick, drive to your local Tyre Pros centre for quick, hassle-free oil changes.