Motorcycle engine oil. We all know what it does but the numbers and letters on a bottle can be confusing. How do you know you’re buying the right oil and what’s the best engine oil for your motorcycle?
Find out with our simple guide.
There are three different types of engine oil and they all have different qualities, strengths, and weaknesses. All oils use additives, even if they’re mineral oils but the semi and fully synthetic oils use more than the mineral oils.
It’s important you get the right type for your engine and the best motorcycle engine oil will always be listed in your owner’s manual.
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.
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.
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.
There are three different sets of numbers and letters on a bottle of motorcycle engine oil that you need to be able to understand if you're going to choose the best type for your bike.
At first it might seem like a lot to take in, but in reality it's pretty straight forward.
The API is the American Petrol Institute and they estabish, test and maintain the ratings standards for the viscosity and content of motor oils globally. These standards enable manufacturers to produce products that meet specific guidelines.
When it comes to motorcycle oil, the first letter you want to look for after the letters API is the letter S. This standard for 'spark' and without the letter S, it means the oil is intended for engines that don't require a spark as part of the combustion process, i.e. diesel engines.
The second letter you're looking for runs from A to N, The further away from the letter A the higher the oil's performance. In fact letters A to H are now obsolete so you'll struggle to find an oil with these letters on the bottle. For any modern motorcycle, you really need oil with the letter L, M or N.
If your oil has API SL, API SM or API SN then it has an AP rating suitable for a modern motorcycle.
JASO standard for Japanese Automobile Standards Organisation and their MA rating was created to make it easy for us to figure out whether or not the oil is suitable for a bike with a wet clutch (where the clutch plates are lubricated by the same oil that lubricates the engine). The MA rating shows you that it'll work with a wet clutch (and be strong enough to lubricate and protect the gearbox). There's also an MA2 rating which is just for more modern four-stroke engines.
For 2-stroke engines the JASO rating is FC or FD, showing that the oil won't cause issues specifically related to two-strokes such as blocking power-valves or build-up of deposits on piston rings which could cause the engine to seize.
This is also known as an SAE rating. SAE stands for the Society of Automotive Engineers. You might have seen oils which have a viscosity of 10W40, 15w50 etc. This is known as a multigrade oil as it has two operating characteristics. These were developed in the 1970s and mean that you don't need to run one engine oil in cold conditions and one in warm conditions.
The W stands for winter and the number that precedes it shows the oil's maximum viscosity (or thickness) at low ambient temperatures (roughly under 10-degrees centigrade). The lower this number the thinner the oil will be at colder temperatures.
The second number (after the W) shows the oil's viscosity at 100°C. The lower the number the thinner the oil.
Always check your owner’s manual for the correct viscosity but listed below are three popular types of engine oil in the Mineral, Semi-Synthetic and Fully Synthetic categories.
A high-end semi-synthetic oil that meets the highest standards. It works perfectly with bikes with wet or dry clutches and is one of the most popular motorcycle engine oils on the market.
It’s just as easy to pick the wrong engine oil as it is the right one. As long as you read your owner’s manual and the specification on the front panel of the oil bottle, you won’t go far wrong. So pick the right oil!
However, the wrong oil could cause you problems. If the specification is close to the actual oil you should be using then any issues will be less likely when compared to using totally the wrong oil.
If for example, you use thin mineral oil when your bike needs a thicker fully synthetic oil then this thin oil may not be able to keep up with the tolerances and stresses in your engine, causing premature wear.
Equally, a really thick (heavy) oil might not properly flow in your engine and this oil starvation could cause lots of problems.
If you really are stuck and you’ve only got one oil to choose from and it’s the wrong oil, it’ll be better than nothing. Just make sure you ride the bike with this choice in mind, keep the revs and speed to a minimum and change it for the correct oil as soon as possible.
Every motorcycle differs, so make sure you check your owner’s manual for the correct way to check your motorcycle’s oil.
However, most motorcycles have sight glass on the engine casing, rather than a dipstick, which is more common on cars.
The sight glass has a minimum and maximum level and your oil needs to sit between the two. You should check your engine oil when the engine is cold (your manual may state differently but it’s unlikely). When the engine is cold, the oil will be slightly thicker but more importantly, the majority of it will have drained down into the sump, rather than be in the upper levels of the engine.
If you check your engine oil when it’s hot, you may end up over-filling the engine which can pressurize your crankcases and may lead to a component failure.
Checking the oil level
Every bike varies. Some have a dipstick and are set up so that you can check the oil when the bike’s on its side stand. Some want you to screw the dipstick all the way in, others want you to unscrew it and rest it on the thread. Check your manual.
If you have a sight glass rather than a dipstick, it’s often easier to check your oil.
If you can, get your bike level (a paddock stand helps) or get a mate / your long-suffering partner to hold it upright for you. Get down on your hands and knees and look at the sight glass. If the oil’s bang in the middle, you’re good.
If the oil is black, then you need an oil change. If it’s milky then you have an issue with water in your engine, which could signify a crack in the engine’s head and is always bad news.
Topping up engine oil
When topping up, be cautious. Don’t tip the bottle upside down and dump in half a litre before checking the level. 100ml can make a huge difference, so add 100ml, then check the level. Repeat this until you’re at the required volume of engine oil.
However, if your engine oil is slightly above the maximum level this is vastly preferable to it being below the minimum level.
Running-in oil is an actual thing, not just an internet myth. Despite many 'experts' saying you don't need to run an engine in these days due to the manufacturing process being that much more precise, you should run an engine in.
The special running-in oil is usually a thinner mineral oil with special additives. It's designed to promote the bedding-in of mating surfaces. It can help remove the machining glaze from cylinder bores and can assist the formation of essential oil-retaining surfaces which reduces the chances of the bores being polished.
Your engine will wear more quickly with running-in oil which is why you should only use it for the specified mileage (usually 500-miles) and you shouldn't use maximum revs.
Will my bike produce more power if I use thinner oil?
In theory yes. A 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.
Do I need to warm my engine up?
While modern engine oils contain additives that can ‘coat’ the surfaces – like the cylinder bores – with oil, it is still important to allow time for your engine oil to flow around the engine. The colder the temperature is outside, the longer it’ll take your oil to reach its ideal operating temperature. If you’re short on patience, try this: fire up your bike and then put your gloves on. By the time you’re ready to go, the engine should be ready too.
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.
Can I use car oil in a motorcycle engine?
This can be risky. Even though you can and will find car oil with the same viscosity ratings (i.e. 10w40) as for motorcycle engines, the additives in the oil will be different. Most cars use a separate gearbox oil and most cars have a dry clutch. So a car oil could make your clutch slip or knacker your gearbox. If you’re buying a bike that’s been run on car oil, beware!
Does engine oil have an expiry date?
Engine oils have an expiry date which means the performance levels can no longer be guaranteed. However if your oil hasn’t been opened, it’ll take years and years for it to degrade. If your oil has been opened and is a couple of years out of date, it’ll most likely be absolutely fine. However, if you’ve already opened it and it’s 5 years out of date you’ll be better off buying fresh oil as the additives in the oil may have oxidised and lost their qualities.
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