…Oil is pretty much all the same right? Well, not exactly as I’ve discovered myself over the years there’s lots of options, grades, confusing sci ency numbers and what does it all mean? In this post i’ll try to explain the basics, as well as the reasons why using the right oil will help to keep your engine running well.

What does oil do?

Oil is your engine’s life blood, not only providing lubrication to the moving parts of the engine but it also prevents corrosion and cleans the engine as well as dispersing heat, all of which helps to prolong the engine’s life.

Oil stops the metal surfaces within the engine from overheating and expanding to the point where the engine would no longer turn (seize up).  Thin layers of oil flow between surfaces, lubricating and reducing friction by cooling the engine as it goes. Some oils also contain special additives and detergents required by some engines to reduce the build up of dirt and deposits helping to prevent blockages and engine wear.

What is oil viscosity?

Viscosity is a measure of the thickness of the oil. The thicker the oil is, the higher the viscosity and the less freely it will flow. The oil’s viscosity grades take into account ambient temperature, that is, how thick or thin it is over different temperatures. If oil is too thick when cold, it won’t flow around the engine as easily when the engine starts. Oil that is too thin when hot won’t provide the right amount of protection to the engine’s moving parts. This is where the numbers come in.

What do the numbers on oil types mean?

The numbers indicate the grade of the oil at a given temperature in relation to its viscosity. In other words how freely it flows when at its lower and higher temperature ranges.

Most modern oils are multi grade oils. This means that as the engine warms up and expands, the oil gets thinner to allow it to keep travelling efficiently through the engine. Multi grade oils have two numbers. The first number is followed by the letter ‘W’ which is the winter or cold starting viscosity. The lower this number is, the thinner it is on cold starts, so 5W/30 is thinner than 10W/40. The second number is the oil viscosity at higher temperatures, the higher the number, the thicker it will stay when hot. So the numbers can be 0, 5, 10, 15, 20, 25, 30, 40, 50 and 60. 0 being the lowest viscosity (thinnest) and 60 being the highest (thickest).

On modern engines it is not only these numbers which count for finding the right oil but also there are extra classifications just to give you more of a headache. These include C1, C2,C3,C4, and so on. These determine which additives are in the oil for particular engines to stop wear and corrosion and prolong the life of the engine. Engines requiring these additives will need them to help stay in good shape.

It is also a common misconception that long life engine oil means not having to change the oil as often. It actually relates to the oil’s protective qualities in prolonging the life of the engine.

Why is it important to use the recommended oil?

Well because of the additives and detergents required by some engines. These help clean the engine as well as preventing the oil from thickening too much, which would lower the protection.

Some oils also contain conditioning agents for engine seals which helps to prevent oil leaks.

Then there’s low SAPS or low ash oils which are required by diesel vehicles with DPF (diesel particulate filters). DPF filters are used to block larger sooty molecules from being emitted from the exhaust system. This helps to reduce the exhaust emissions.  Low SAPS oils are low in sulphated ash which otherwise could cause the filter to block irreversibly, leading to potentially expensive repairs.

Oils which are high in phosphorus and sulphur can also have a detrimental effect on the efficiency of catalytic converters. These are designed to convert pollutant gases into less harmful ones. So choosing the right oil is important for both petrol and diesel vehicles.

There is of course a bit more to it than that. I’ve covered the basics here which is a good start and maybe all you will ever want to know.

The manufacturers recommended oil for your car can usually be found in the owners manual but If you can’t find it and are still not sure which oil you need for your car, contact us and we’ll be happy to help.


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Published by Yvonne Garman

Since 2002 I've helped my husband Scott run 'The Organic Mechanic', our garage in Devon. I mainly take care of the admin and accounts side of the business and leave the mechanical wizardry to Scott, although it's not unknown for me to help him out from time to time. I came up with the idea of Auto Snakpax when I realised that many people didn't know what oil they should be using to top up their cars and the importance of it. When I started the website It lead me to the idea of this blog to address some of the things that our customers have asked about over the years, whether it's how to check their oil and other relevant maintenance they can do, or about cars that we've had in for repairs that have sparked interest. So here it is. I hope that you'll find something useful or interesting here and thanks for visiting our blog.

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