Best motorcycle oil | Fully / semi-synthetic, weights, API and more explained

“What’s the best oil for my engine?” It’s a question asked by many and answered by even more (though rarely accurately). To really understand how to choose the right lubricant for your motorcycle (or car), you need to understand how oil is made, and what the ratings – like JASO and API – actually mean.

BikeSocial spoke to Martin Wabnegger from Motorex, at the factory in Langenthal, Switzerland. And we didn’t stop until he’d answered every last one of our questions.

Motorcycle oils account for about 30% of the company’s business, which has been family-owned since it was founded in 1917. The factory takes refined and synthesised base oils and additives, mixing them to create not just the only lubricants recommended by KTM, but fluids ideal for Honda, Yamaha, Suzuki, Kawasaki Triumph, Royal Enfield and many more (not to mention cars, trucks, boats, trains, chainsaws... oh, and Touratech suspension).

Martin Wabnegger from Motorex in Switzerland

If you want to know everything about oil, read on, but if you’d rather skip to your most burning questions right now, click the links in the Table of Contents.

Why does an engine need oil?

According to Gesellschaft für Tribologie (the German Society for Tribology), 5% of GDP is lost to friction in industrialised countries. In Germany, that’s about 35 billion Euros every year. Tribology is the science and engineering of friction, wear and lubrication, in case you wondered.

Wherever parts are moving, friction is created. Friction creates heat, which is a loss of energy. So besides the fact that parts will wear out very quickly without oil, there are significant losses in the energy that’s being produced.

Theoretically, parts could be very, very highly polished to create smooth surfaces that rub against each-other, but to get to the point of being truly smooth (not just looking smooth to the naked eye) is extremely expensive, and unachievable in mass production.

Friction is caused by the hooking up of rough surfaces (1) and adhesion between surfaces (2)

Under a microscope, the surfaces of the parts inside your engine will look very rough, and in use those peaks catch and rub on each-other. You need something to go between the two surfaces, which is where oil comes in.
Engine oil has six main purposes:

• Lubrication

• Cooling

• Sealing

• Cleaning

• Corrosion protection

• Reducing noise

Of course, the manufacturer needs to ensure the oil can do all of that – through the use of a base oil and additives – as well as being mixable with all other common engine oils, prevent sludge, resist foaming, minimise evaporation, ‘stick’ to surfaces, leave no deposits, work with any seals, be compatible with all metals, lacquers and specialist coatings, and work across a range of temperatures.

What are the different types of friction in an engine?

Not all friction is the same – some’s easy to deal with, and some is really tough on oil…

Sliding friction: You’ll find this between the piston rings and the cylinder as the piston moves up and down.

Rolling friction: This occurs in ball bearings for instance.

Combined friction: This is found in gearboxes, and it’s the most demanding on oil. This environment is harsh too, as the gears’ teeth roll and slide over each-other at extremely high pressures on a single point; it’s why cars use a different oil in the gearbox to the engine, and the first clue as to why you should not use car oil in a motorcycle.

This long row of pipes all have finely-controlled valves that add just the right amount of additives to the base oils during mixing. Some additives are added manually, and a sample of every batch of every product that Motorex makes is kept for five years.

How is motorcycle oil made?

Making any oil is just like making a soup – it’s a recipe. All the ingredients are available to every manufacturer, but what’s different is which is used and how they’re mixed.

It starts with crude oil, which isn’t a consistent raw material – it’ll have various impurities like sulphur, water and heavy metals. 80-85% of crude is carbon and 10-17% is hydrogen. Up to 7% is sulphur (or sulfur if you're in the US), which can be harmful to the performance of the oil and cause corrosion. The rest will be things like nitrogen, chlorine, phosphorus, sodium, magnesium and vanadium. The quality of the raw crude will vary depending on where in the world it came from (apparently North Sea oil is pretty good stuff)

Base oils require a second step in refinement at 350°C in a vacuum, which is a step beyond that needed for petrol (350°C at atmospheric pressure). That’s why it costs more than petrol.

After refining, mineral base oils are distilled into three groups:

Group I has less than 90% saturates (higher saturates relate to a stronger molecular bond) and more than 0.03% sulphur. The viscosity index of a Group I mineral base oil is 80-120.

Group II oils are more than 90% saturates, with less than 0.03% sulphur.

Group III oils require yet another step after distillation – hydrocracking – where a catalytic surface at 500°C and 200 bar cracks the hydrocarbon molecules, leading to an ‘HC base oil’ that’s as pure as the Group II oils, but has a viscosity index over 120 – this is good as it’s more stable at higher temperatures. Basically, the long chain of hydrocarbons will crack under pressure, so cracking it in the refinement process means the loads during use are spread out over more molecular chains.

What’s the difference between mineral, semi-synthetic and fully- synthetic oil?

Groups I, II and III base oils are all mineral. Beyond those are group IV, V and VI, which in the EU are the only ones classed as fully-synthetic. In the US, Group IIIs can also be called fully-synthetic. But there’s more…

All engine oils have synthetic additives, regardless of if they use a mineral base oil. The additives will be for shear strength, cleaning, wet clutches and many other purposes, but a manufacturer will often have to use more additives in a lower-quality base oil. And additives can be very expensive – some cost up 20,000 Euros for a 200 litre drum.

Group IV oils, or PAO (poly-alpha-olefins), while classed as fully-synthetic, are Group III base oils that are further cracked to single molecules – it’s an engineered oil, sometimes known as a non-conventional base oil (NCBO), with a high viscosity index, lower friction and a lower Noack (a test of evaporation) value. It’s more expensive though.

Group V oils are anything that isn’t included in the above, like ester, which comes from plants and other living things – it’s not refined from crude oil. Ester is the best base oil, but it can’t be used on its own; some brands will claim their oil is 100% ester, but that’s only the base oil; without additives, it won’t work in an engine.

Ester’s got an even higher Noack value, the molecules are naturally attracted to positively-charged metal surfaces to create a protective film, and it’s more biodegradable. But it needs additives to prevent it ruining the seals in your engine, and it’s expensive.

Group VI oils are PIOs (poly-internal-olefins) – similar to PAOs but with a higher viscosity index.

This massive sculpture of Einstein is made of motorcycle parts, and sits on the wall at the Motorex factory

Is cold-starting an engine bad for it?

It can be, absolutely – if the oil has all drained away from the surfaces inside the motor, when it’s first turned over it will be running dry for up to one or two minutes if it’s a really cold climate.

Modern oils are designed to leave a layer of lubricant on all the moving parts, even after it’s been run. To do this, oils use ‘polar’ additives, which chemically or electrically ‘stick’ to the molecules of the metal surfaces. You need a different additive to make the oil stick to aluminium than you do to iron or the coatings often used on pistons and bores. That’s why you must use the recommended oil type for your engine.

Equally, the seals must kept lubricated, so any additives used in the oil need to work with the rubber and other materials.

Do I need to warm my engine up?

A good quality oil with have a polar base and additives that leave a thin coating on the engine’s internal surfaces, to reduce wear at start-up. But the colder the ambient temperature is, the longer it’ll take for the oil to get around the engine. Thrashing your bike from the moment it’s started is going to damage it – I usually fire it up, then put my gloves on, and ride away gently.

Bouncing it off the limiter from cold to show off your noisy exhaust is a quick way to ruining your motor, and having damaged a CBR600’s top-end by doing repeated starter motor tests for an article – never letting the oil fully pump around the motor – I know that it’s important to just start the bike and give the lubricant a chance to get moving.

So a good thick layer of oil between two surfaces is the best bet?

No – too much oil is a bad thing, and will cause hydrodynamic and hydrostatic friction.

Two bare surfaces result in solid body friction. A cylinder bore, for instance, will likely have a coating on it, which separates the two surfaces and creates dry, or boundary friction, but the polar additives will also help protect the surfaces with a film or layer.

The next step is to get oil in between the microscopic peaks, allowing the load to be shared between the oil and the surface peaks (coated with the thin film) of the objects in contact. This is the ideal scenario, with minimal wear and the least amount of friction.

Too much oil – completely separating the two surfaces – leads to the oil taking on all of the load and fluid friction occurs. There’ll be no wear, but you’ll lose power.

As the separation of the two objects increases due to excess oil, the coefficient of friction gets greater thanks to hydrodynamic friction

What does 10W40 mean?

You can buy oils in various viscosities, such as 0W20, 10W40, 15W50 and more. These are ‘multigrades’, which is what most engine oils are now. The ‘W’ stands for winter, and the number before it relates to the maximum viscosity (or thickness) of the oil at low ambient temperatures such as 0°C and 10°C.

The second number relates to the viscosity of the oil at 100°C, so a 30 is thinner and less stable than a 40 at 100°C.

You’ll often find a range of oils recommended in your bike’s handbook, based on the climate where you use it.

Does it matter what viscosity of oil I use?

It’s important to use the correct oil for your engine, but if for some reason you had to use something else, a 10W50 would cover the range demanded by an engine that’s designed for a 15W40 oil as the first number is lower and the second is higher. Equally, that means a 10W40 is no good for an engine that should have 0W10 (as the first number is higher) or one that needs a 15W50 (the second number is lower).

The wider the viscosity range of an oil between ambient temperature and at 100°C, the more expensive it will be. But if there’s a warranty issue with the engine, the manufacturer will be looking to see that you used the oil that was specified, so there’s rarely a benefit to using an oil with a wider range than that specified.

What do the JASO MA and API specifications mean?

Over the years, engines have got more and more efficient, thanks to tighter tolerances, which means that oils have had to progress too.

The API rating found on oil relates to the American Petroleum Institute – the rating has changed over the years to reflect advances in engine technology, and is currently at ‘SN’. You might find some Far East commuter bikes have an API oil requirement that’s as far back as SG (from the early 1990s), but remember that this is not taking into account the clutch (see the JASO MA information below).

Some older oils, rated between SA and SE, can potentially cause harm in more modern engines, but an oil with a more up-to-date rating (it always starts with an S, then is a letter going up through the alphabet), tends to be backwards compatible, at least over a few years. But still stick to the requirements as some seals might not be compatible with a fully-synthetic oil for example.

If you have a much older bike, you might need to consider a ‘classic’ oil like Classic Motorex as paper gaskets aren’t compatible with all modern oils, and where an engine doesn’t have a filter, it should use an oil that ‘dumps’ any deposits in the sump, rather than carrying them around, looking for a filter to scrub them away.

Car manufacturers will use very specific codes for the oils required in their vehicles – as long as the buyer uses that code, they don’t need to worry about the viscosity. But motorcycles don’t have such specific ratings, so the API codes are a broader range, and also won’t give a very accurate indication of quality.

This Motorex Power Synt oil has the API and JASO certification labels (with registration codes), which proves it’s been tested to meet the requirements

You should see mention of JASO MA (Japanese Automotive Standards Organisation) on most motorcycle oils. MA relates to a spectrum of dynamic friction characteristics – the oil must sit between a range of 1.45 and 2.5 (it also includes the Noack test for evaporation). An oil tested to JASO MA 1 will be fine between 1.45 and 1.8, while an engine making higher torque might demand MA 2, which covers 1.8 to 2.5. One that meets JASO MA covers the entire range.

And that’s it – to meet the requirement of JASO MA, the friction characteristics just need to be within those limits; there’s no benefit to ‘exceeding’ them.

Your bike might require MA1, so putting MA2 in won’t hurt it, but it’s unnecessary; MA2 is not a ‘better’ oil than MA1.

MB-rated oil is designed for scooters with CVT (continuously variable transmission).

The JASO standard was invented by the Japanese bike manufacturers when they had the first bikes that were making 100bhp. Back then car oils were used, but the clutch was starting to slip. The level of friction required was determined, and JASO MA was introduced.

Where an oil manufacturer might want to exceed the levels required for JASO MA is in motocross racing, where the greatest demand on the oil is preventing the clutch from slipping. For that 45 minute race, a specialist oil might focus primarily on protecting the clutch.

One thing to understand is the difference between an oil that ‘meets the requirements of’ the JASO test standard, and another that has been independently tested. There’s no legal requirement for an oil manufacturer to have their oil tested – they can ‘self-certify’ the oil themselves. Take a look at the labels to know…

This manufacturer says that the oil meets the requirements of JASO, but it hasn’t had the product independently tested

How important is it to change the oil at the recommended intervals?

You need to change oil because it wears out, though it’s the additives that mainly wear first; for instance, oils with polar additives that make them stick to surfaces will remain in place only until the additive is destroyed, so changing your oil at the recommended interval is very important. The engine and the oil manufacturer will have worked to make sure the oil can last the time necessary under normal working conditions.

A bike manufacturer will specify what viscosity of oil its engine needs, and how often it must be changed. Motorex has a very close working relationship with KTM, so when the Austrian bike builder is developing an engine, it works with Motorex to ensure a suitable oil is achievable – there really is more to it than slapping a Motorex sticker on the crank case.

As oil will also start to degrade over time, don’t be tempted to leave it in if you’re not doing many miles. While it is worth spending the money on good quality oil, the most important thing when it comes to maintaining any vehicle is that you change the oil regularly.

Can I get more power by putting a thinner race oil in?

Remember that using the incorrect oil can not only cause the ‘gaps’ between moving surfaces to fail to be filled, it can also lead to reduced power due to hydrodynamic friction. Using an oil that has a lighter ‘W’ viscosity can help increase power by up to 3-5% – it’s why Motorex developed the 0W40 for Crescent Suzuki – but the tolerances are very tight, and a race bike is running at a very consistent temperature all the time; quite unlike a road bike. And it gets changed after every race.

If you put a race oil in a cheaply-built bike for instance, you’d be unlikely to get the same advantages as the tolerances are moor wide.

Road bikes – with their broad temperature ranges and infrequent oil changes – are in many ways far more demanding on oil than track bikes (though enduro bikes are harder still as they get thrashed in all kinds of temperatures).

Can I use car oil in a motorcycle?

Car oil is designed to work in the engine, with a different oil in the gearbox. And the clutch is usually dry. Besides the fact that bike engines usually rev a lot higher, the oil in the engine also has to have additives that help it work with the much higher loads of a gearbox. Added to that, further additives will be used in order to work with the wet clutch inside most bikes.

You can buy a cheaper car oil with the same viscosity as a motorcycle oil, but it may not have the additives necessary to make stand up in a bike, and it won’t be guaranteed to work with a wet clutch.

Many people will claim they’ve had no problem using car oil in a motorcycle, but without certification to JASO-MA, there’s no guarantee that the additives used will be compatible with a wet clutch. They’re also unlikely to have stripped the engine after several thousand miles.

Personally, I’d always buy an oil designed for my motorcycle, and I’d only buy a used bike that had been regularly maintained with the correct oil.

Can I mix engine oils if I need a top-up?

Oils have to be designed to be compatible with others, but it’s not advisable as you’ll be mixing the qualities and abilities of them. A bike manufacturer isn’t allowed to tell you that you can only use one brand of oil – they can only advise you – but it’s best to stick with one brand between oil changes.

Of course, if your bike is getting low on oil, top it up with whatever you can (as long as it's the correct grade and spec) – it's always going to be better than running an engine dry!

So I don’t have to use the brand of oil that my handbook suggests?

No, but remember that companies might have worked together during development, like KTM and Motorex. And it can – if very rarely – be a case that you absolutely must use exactly the right oil, but it will be part of the specification…

The 2007 KTM 690 used silver-plated bearings, but the oil manufacturers weren’t informed. It soon became clear that the oils were stripping the plating off, leading to a lot of recalls. A new oil was quickly developed with Motorex that was safe for this engine, and was shipped with every new bike, before the plating process was dropped from later models. The 2008 models carried a warning in the owner’s manual, but it’s something worth knowing if you’re buying a used one around that age that hasn’t had the bearings replaced…

You often won’t be aware of early engine damage without stripping the motor down.

I won’t keep the bike long, so don’t really need to worry about the oil, do I?

A particularly poor oil, like those sometimes found in Asia and Africa, can cause excessive wear in just a couple of thousand miles. In Europe, it’ll typically be tens of thousands before any real difference could be seen; it’s more likely to be the third or fourth owner that notices if a lower quality oil’s been used. Karma’s a bitch – don’t be that careless owner!

When buying a used bike, ask to see the receipts for the oil that was put in the engine, just in case you find out you’re buying from someone who doesn’t think it matters if they put in the cheapest thing they can find (or even car oil!).

What’s a running-in oil?

Typically, manufacturers will use a lower-quality oil for running in, as they want the moving parts to bed in and perfectly fit – a little wear is desirable. The first couple of hours use for any engine can determine if it’s going to be a ‘good’ or a ‘bad’ one; race bikes are typically run in on a dyno.

However, off-road bikes will often come with a high-quality wide-range oil – like a 10W60 – as they’re usually thrashed from the moment they’re purchased, and could be worked in any number of environments.

Why does my engine burn oil?

Oil evaporates. It’s common to hear people saying that their engine is burning oil, thinking it’s getting past the piston rings, but usually it’s the very high temperatures inside the motor that are causing it to disappear.

The Noack volatility test (named after Kurt Noack) is a standardised laboratory measure of the amount of oil lost to evaporation at a 250°C.

The engine’s combustion chamber can reach 2,500°C, while the valves can hit 800°C and the bore 300°C. The oil in your engine will reach different temperatures as it moves around the motor, and it’s mainly the base oil that evaporates, not the additives, but the Noack figure gives you a good comparison of different oils.

A typical engine can reach very high temperatures, and if the oil is doing some of the work of cooling it, evaporation is even more likely.

A cheap base oil (SN 100 in the graph below) loses 29% of its weight during the Noack test; the minimum level required for a motorcycle oil to reach JASO MA is 20%.

A typical OEM 15W40 running-in oil will lose 12.7% (part of the reason it needs changing after just 600 miles), while a pure fully-synthetic ester base oil will lose just 5%. A premium oil like Motorex’s Cross Power 10W50 will lose 5.1%.

The Noack test shows how oil evaporates

BMW’s air-cooled motors had a reputation for ‘burning’ oil, but most losses were down to evaporation, not poor tolerances – it’s why Motorex’s Boxer 15W50 oil was created, after a German BMW specialist approached the company wanting to eliminate the need for long-distance riders to carry a spare litre. As this isn’t a fully-synthetic oil, it’s the additives that help to reduce the evaporation to 6.8%.

As any oil that evaporates is lost through the crank case breather and out into the airbox, the evaporated oil is technically burned as it’s sucked into the combustion chamber, but not by washing past the piston rings, as many people would believe. Unless an engine’s very badly worn of course – if it’s got well over 100,000 miles on it and it’s using a lot, it can be worth using a heavier oil, as the tolerances will have changed.

When’s the best time to change oil – before the bike’s stored or after?

Oil should be changed at the manufacturer’s service intervals, which is typically a certain mileage or 12 months, whichever comes first. But what if you put your bike away for winter? Should you change the oil then, or in the Spring when you take it out again?
Always change the oil BEFORE you lay the bike up, as the deposits in the oil from the summer of use will sink, and lay in the engine.

If the bike’s being stored for much more than a year, it’d be wise to change the oil before it’s stored, and again when it’s taken out of storage.

Does oil go off? How long can I keep it for?

As soon as oil meets air, it starts to oxidise. It’s slow though, so if – like me – you have some oil left over after a service, and intend to use it as part of the next service in 12 month or less, you’ll be fine. It’s worth squeezing as much air out of the bottle as you can though, and be sure to use that oil first in the next service.

Motorex offers dealers ‘bag in a box’ oil, which keeps the oil fresh as the bag contracts with the oil, so air never reaches it; a good idea for the less-commonly used products, but it’s only in 20 litre containers, so is costly for a home user.

If you see the oil go dark quickly, it’s more likely an indication of the previous lubricant’s quality…

I put new oil in my engine, but it went black straight away, or it started using oil. Is it rubbish?

No… it’s more likely that the new oil is better than the old stuff that was in there – the additives that have been used are doing a good job of cleaning the old deposits from the inside of the motor.

Also, when you use a new oil with better cleaning properties, it can clean some deposits out that end up meaning a little oil can now get past the piston rings and be burned. This isn’t a sign that you’ve put a poor oil in. Over time, unless the engine is really old and badly worn, the rings should be able to move around and create a good seal again.

If you buy a used bike, and you believe a poor lubricant might have been used, it could be worth changing the oil, running the bike for a couple of weeks, then changing it again, so all the deposits that the quality oil has cleaned out aren’t pumping around your motor for 12 months. Personally, whenever I buy a used bike or car, unless it’s very new (rare for me), regardless of if I’m told it’s ‘just had a service’ I’ll always service it again.

What’s the difference between a good and a not-so-good engine oil?

Motorex’s oils are either a mix of Group V and Group VI base oils (the Group IV oils help balance the problems with ester, something other brands might do with further additives), or they’re Group III.

But any oil will be around 80% base oil (of which there’s a choice of about 70), and 20% additives (from a choice of about 600). A typical fully-synthetic lubricant might be made of two base oils and 10-20 additives. An oil might only use a mineral base, but it’s technically semi-sythentic as soon as the first additive goes in.

A lot of marketing work goes into promoting oils, and measuring their performance is hard, given the variables and the different intended uses each has. Every motorcyclist will have a favourite that they believe is best for their engine, but as any excessive wear will be very hard to see over the typical ownership of a bike in the UK and Europe, the truth is harder to nail down.

Ultimately, it’s the quality of the base oils, and the quality and quantity of the additives used that will determine how well your oil cleans your engine, how well it maintains particles in suspension to keep them away from crucial bearing surfaces, how well it resists corrosion, how effectively it coats the internals, how long that coating lasts… and so on.

If you want to get more analytical, take a look at the datasheets online for an oil you’re considering. If you understand what the base oils are, and what the Noack test is, you should be better placed to at least start to decide which lubricant you want to buy.

Ultimately, the best oil is the one that’s changed regularly, and that meets the requirements set out by the bike manufacturer (a fully-synthetic oil is not always the best for your bike). There’s no point in buying an oil that has a higher specification (viscosity, API or JASO rating) than is required, but the more expensive oils will most likely use the best base-oils and additives.

I only use high-end brands, and I always make sure it’s the correct viscosity, and that it’s certified to be compatible. My bike cost me a lot of money, and the oil is its life blood…