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What does 10w40 mean?
10w40 engine oil is a 4-stroke engine oil designed to lubricate the moving parts. You can buy it for generic applications (cars, motorcycles and other engines) and also motorcycle-specific oil.
The numbers and letters refer to the oil’s viscosity. That is to say it’s thickness. 10w40 is just one type you can buy, you can buy many others, such as 10w30, 15w50 and so on.
These oils are known as multigrade oils as they have two distinct viscosities at two set temperatures.
What is viscosity?
This is a liquid’s ability to resist motion (flow). Water has a low viscosity (it flows easily, even at cold temperatures) Whereas Golden Syrup has a high viscosity (try pouring some through a plastic straw).
How is engine oil viscosity measured?
The oil thickness is usually measured at 0°C and 100°C.
At 100-degrees, the oil will obviously be a lot thinner, whereas at the temperature that water freezes, oil won’t freeze but it will be noticeably thicker.
The W standards for winter. The number before the W relates to its maximum thickness (viscosity) at that colder temperature. The number after the W refers to the oil’s thickness at the warmer temperature.
This can be confusing as some people also refer to an oil’s ‘weight’ and that is to say, it’s thickness. A ‘heavy’ oil doesn’t flow as well as a ‘light’ oil.
A 10W40 oil (and indeed any multigrade oil) contain VI improvers which change in character as they warm up. This means that a 10W40 oil has less viscosity than a regular 40 weight oil when cold though not as little as a straight 10.
This oil is ideal as it’ll have the right characteristics whether the engine’s cold or hot.
Do I need 10w40 oil?
If this is the grade that is specified in your owner’s handbook then it’s the one to go for.
The oil’s thickness makes a difference. If it’s too thick, it won’t flow around the engine well, potentially starving key areas of oil and causing the engine to seize.
If it’s too thin, it might not stay in areas of the engine, which can be a problem when the bike has been left standing, as the engine is cool and gravity will have meant the engine will collect in the sump. When you fire up your motorcycle, engine damage can be caused in those first few moments. If the oil is too thin, there won’t be enough of a film clinging on the surface of the moving parts to protect them.
Different 10w40 engine oils
Your motorcycle might require semi-synthetic (or part-synthetic), fully synth or even mineral oil. So what are they and how do you know which one you need?
Semi-Synthetic 10w40 motorcycle engine oil
Sometimes referred to as part-synthetic, it’s simply a blend of mineral oil and synthetic oil. The ratio is usually around 25% synthetic to 75% mineral but the ratio varies and some of the more expensive semi-synthetic oils have a higher ratio of synthetic oil to base oil. Semi-synthetic oils offer a great balance of performance and value for money which is why it’s the most popular oil type for all motorcycles.
Fully Synthetic 10w40 motorcycle engine oil
Synthetic engine oil is an oil that’s almost entirely man-made. Engineered in a laboratory, if you will. It is usually comprised of a blend of over 90% synthetic and under 10% base (mineral) oil. It will protect against engine wear more than a mineral or semi-synthetic oil but it’s much more expensive too. It won’t degrade as quickly as oils that use mineral oil and it’s capable of operating under far more strenuous conditions without the properties changing. This is important if you’re running a high-revving or high-power output motorcycle, like a sportsbike.
Mineral 10w40 motorcycle engine oil
Sometimes known as ‘regular oil’ this is refined crude oil and is the least expensive. It’s often a by-product of the petrol-refining process. It’s a good oil to use for basic engines, think low-revving low power output engines such as those in standard road bikes, Harley Davidsons, 125cc motorbikes and scooters. Due to the lack of additives, mineral oil requires changing more frequently than a synthetic oil as it’ll lose its properties quicker than a synthetic oil but it’s still good value for money.
The best 10w40 motorcycle engine oil
There isn’t really a ‘best’ when it comes to engine oil as all oils perform differently, depending on the engine size, layout and often manufacturer.
Below we list some of the most popular brands on the market.
Castrol’s motorcycle engine oil offering in the 10w40 variety is called Castrol Power 1. The Power 1 is a part-synthetic oil whereas the Power 1 Racing version is a fully-synthetic oil, designed with high-revving, high-power motorcycles in mind. Some see Castrol as the best motorcycle engine oil.
Motul offer a large selection of 10w40 engine oils for motorcycles in scooters. They’re available in 1-litre and 4-litres sizes and they also make a scooter and maxiscooter-specific engine oil.
The different numbers in their oil, 5000, 7100, 5100 all refer to the make-up of the oil, i.e. whether it’s part-synthetic or fully synthetic.
Shell’s motorcycle engine oil range is called ‘Advance’. You can pick up 10w40 in most of their petrol stations but you’ll be lucky to find a motorcycle-specific oil in most of their stores. However, it’s easily available online. It’s sold in 1-litre and 4-litre bottles.
Silkolene is another popular motorcycle oil supplier. Their range is called Scooter, Super, Comp and Pro and this refers to the quality of the oil and its make-up. Super for example is a semi-synthetic engine oil that’s perfect for commuters and tourers. While Pro 4 is a fully-synthetic oil designed for superbikes.
Where can I buy 10w40 engine oil?
You can buy 10w40 oil from high-street motor factors, car and motorcycle dealerships, Halfords and also some large supermarkets like Asda and Tesco will also stock engine oil.
You can even buy it from home supply retailers such as Argos, Wilkos and Robert Dyas.
These retailers will stock a variety of well-known brands like Castrol, Motul and Silkolene. Some, like Halfords and Tesco, will also sell their own brand of engine oil.
If you want to buy it online, you have various options but here are some handy links:
What’s the cheapest 10w40 engine oil?
Engine oil tends to come in 1-litre or 5-litre sizes. The small size is good for topping up while the large size is good for a full oil change.
The cheapest 10w40 engine oils cost around £5 per litre, most motorcycle-specific engine oils cost around £8-10 per litre while the most expensive are around £15 per litre.
The cheapest engine oil tends to be an own-brand, i.e. Halfords or Tesco’s own.
10w40 engine oil FAQ
Frequently asked questions about the most commonly used engine oil.
Can you use car engine oil in a motorcycle?
It is always worth going with your manufacturer’s recommended engine oil. Especially if you own a high-revving motorcycle, as this is the main difference between oils developed for cars and motorcycles.
As a ‘get you home’ measure, any oil is better than no oil but motorcycle-specific oils contain additives that help them deal with things like high-revs and prolonged periods of time where the bike is left idle (motorcycle oils tend to include more corrosion inhibitors than car oils).
Is there a motorcycle engine oil finder?
The best one we could find is this one by Motorex. It works best if you type in your motorcycle model rather than start with the make.
What tools do I need to do a motorcycle engine oil change?
We have written a best motorcycle engine oil guide, which includes a section explaining how to change the engine oil in your motorbike.
Is motorcycle-specific engine oil a con?
While it is generally more expensive than a generic or car engine oil, motorcycle-specific engine oils have additional additives that help them run at higher revs (without shearing) and some contains other additives that help prevent corrosion (motorcycles tend to be left for months at a time). So while they are more expensive, they do more for your motorcycle.
What is 10w40 running in oil?
This is engine oil designed to be used for brand new or rebuilt engines. It is a natural engine oil (ie mineral) and it will help the bedding-in process of your piston-rings and the cylinder bore. A semi or fully synthetic oil is too slippery for this process to work properly. The running-in oil is designed to be used for a short period of time (usually 500 miles), after which it is drained and replaced with regular 10w40 engine oil.
Will my bike produce more power if I use thinner oil?
In theory yes. Thinner engine oil will have less resistance to flow and using a thinner oil could increase your motorcycle’s peak power by as much as 5%. While some race teams use thinner oils, they are working to very strict tolerances and controlled operating temperatures, whereas, on your road bike on the road, the oil needs to work at a greater range of temperatures. It’s simply not worth risking the engine’s life, by running a thinner oil.
Does cold-starting wear an engine?
Yes. However modern engine oils are polarised, meaning they can ‘stick’ to the engine’s internal surfaces, reducing wear. This is why it’s important to give your engine oil a minute to circulate around the engine when you first fire the bike up, to minimise the wear.
Can I mix engine oils?
It’s always best to use the same viscosity or the same brand of engine oil, to ensure that the properties of the oil meet the standards that your engine requires for the oil to properly lubricate it.
However, if you’re running low on oil, you need a 15w30 but there’s only a 10w40, you can certainly top-up your oil but remember – the further you move the oil away from the manufacturer’s intended specification, the more likely you are to cause wear to your engine.
How much oil do I need for my motorcycle?
Most motorcycles will require between 2-4 litres of engine oil. So if you’re doing a full oil change, it’s probably cheaper to buy a 4-litre bottle of engine oil.