Spannerman: What’s the best oil for your motorcycle?

Spanner looks at the problem that keeps proper motorcyclists awake at night: what’s the best oil I can use in my bike?

It’s not your fault if you’re a bit confused. There is fierce competition out there in consumer-land to get you to commit to certain brands of oil. It’s particularly fierce in the motorcycle industry where, compared with four-wheelers, far more riders do their own servicing.

Oil companies tie themselves to racing success (Repsol), history (Castrol), patriotism (Penrite) exoticism (Motul) and technology (Mobil). The packaging is a blend of selling the product and confusing the consumer with performance claims (what’s the difference between MA and MA2 on the JASO standards – come to think about it, what are the JASO standards and why should I know about them?).

You can’t just give up, though. If you buy a new bike, you’ll probably follow the service schedule laid out in the owners’ handbook. This tells you what type of oil to use (10W-40) usually without specifying a particular brand, although some manufacturers have tied themselves to a particular company and only recommend that brand. Ducati recommends Shell Advance and Triumph has tied itself to Castrol. “Cool,” you think. “If Ducati says it’s the right oil, that’s what I’ll use.”

While you shouldn’t have any reason to doubt the advice, the truth is these relationships are often commercial rather than based on science. It benefits Shell to be associated with such a powerful brand as Ducati and it will be paying for the privilege.

Similarly, some bike manufacturers sell lubricants with their own branding on it. Harley-Davidson has its own oil, as do many of the others, including Yamaha and Suzuki. None of them actually produce the oil themselves, though. It’s provided by an existing oil company and simply rebranded. You can reliably expect if you pay the extra money that the oil will do its job – bike manufacturers have too much to lose if they get it wrong ­– but you don’t have to tie yourself to the bike-branded product to get the best results and, indeed, better options may be available.

It is possible to get it wrong, though. There was the infamous case in the 1980s of Shell recommending XMO for bike use and owners reporting a doubling of oil consumption which wasn’t reversed when they stopped using the oil.

This brings us to important point number one: there is a difference between motorcycle-specific oil and general automotive oils so whatever decision you make, choose between the motorcycle-specific oils and leave the car oils for the cars.

If you buy a new bike it makes sense to have at least the first service done by the dealer as an oil change won’t be the only thing going on in the service and inspection process. Yes, you might decide to have dealer-servicing for the entire warranty period but keep in mind you won’t void the warranty if you have the oil changed by a non-aligned mechanic or if you do it yourself – as long as you comply with the recommended quality and quantity of oil.

Oil is your bike’s best friend

The lubrication system inside your bike’s engine is the most important thing in the life of the bike. Making sure it’s right will give you the longest possible service life and the most reliability. While the primary role of oil is lubrication (providing a layer of protection between the moving parts), it does a lot more.

It cleans the inside of the engine and holds the bad bits it picks up in suspension so they can be collected as the oil passes through the filter.

It neutralizes the corrosive acids formed as part of the combustion process so that they don’t eat the engine out from inside.

Oil cools the internal components it comes into contact with including the gearbox. Remember the period prior to widespread liquid cooling where the cooling was often described as ‘air-oil’? That usually involved oil being directed to the underside of the pistons.

Doing all that work, though, means oil doesn’t last forever.

Motorcycle manufacturers will recommend oil change intervals where they believe, under normal operating conditions, the oil will cease functioning as it should and will need to be changed. If it isn’t changed, it will cease its cleaning function, it will oxidize (‘free radicals’ will start corroding inner parts), acids will no longer be neutralized and will join the corrosion process, sludge will build up potentially blocking oil passages and increased friction will start wearing out the moving parts of the engine including the head(s) and the pistons.

It’s a no-brainer, isn’t it? If your bike came with a service booklet, make sure you fill it in every time the oil is changed by a dealer or anytime you do it yourself. When the time comes to move your bike on, nothing will give a potential buyer more confidence than a full service history.

Oil deconstructed

All oils start from a base stock which is usually around 85 to 90 per cent of the finished product. While much is still petroleum-based (mineral oil), semi-synthetic (a mix of mineral and synthetic oil) and full-synthetic base stocks are now in much wider use.

While these base stocks can come from a variety of providers, it’s essentially a level playing field for oil manufacturers. The differences in the finished products come from the type, quantity and quality of the things added to the base stock.

A typical engine oil has a number of additives. Foremost are anti-wear additives which reduce the friction between moving parts. Phosphorous and zinc are common. Penrite’s 4ST labeling tells us it’s ‘full zinc’ meaning it has lots of zinc as its main anti-wear additive.

Detergents and dispersants are also added. The detergent cleans engine internals and the dispersants keep the results in the body of the oil so they can be collected at the oil filter. Without the dispersants, the crud would sit on the bottom of the engine and eventually cause trouble. When you wash the dishes they come out clean but if it’s a particularly greasy wash, you’ll be left with fatty sediment in the sink. Detergents and dispersants stop this happening inside your bike’s engine.

Motorcycle oil also has corrosion inhibitors and acid neutralizers. The combustion process produces some very toxic acids and additives like calcium and magnesium work to absorb these acids.

Additives will also include viscosity index improvers or viscosity modifiers. Something described as a 10W-50 oil will act like a 10W oil when it’s cold but will perform like a 50W oil when it’s hot. Sounds great, doesn’t it? You get a light oil from start-up which will pump quickly through the engine but when it’s really hot, it will provide the heavier viscosity for added protection.

Viscosity modifiers are complex polymers that ‘swell’ when the oil gets hot so the oil maintains its integrity and doesn’t get too light to provide protection.

Here’s a very unscientific way of explaining how these polymer strings work (and what’s potentially wrong with them). You know those whistles you get at kids parties where you blow through the plastic end and a paper tube scrolls out? When you stop blowing, the paper tube rolls back ready for your next blow. Imagine something like that being suspended in your bike’s oil which is activated when the oil gets hot and which retracts when the oil cools down. Most of us have cleaned up after birthday parties and noted the whistles don’t last very long. There’s a limit to how many times they can expand and retract and polymers in oil are the same.

Logically, a 5W-70 oil should be ideal with super-quick circulation from cold and massive protection when the oil is hot. When you bulk up an oil like that, though, it can cause circulation problems in narrow passages and potential starvation, As well, when the polymers are exhausted, you’ll be riding around with a 5W oil only and your bike’s engine will hate you for it.

The lower the gap between the two numbers, the lower the task of the viscosity modifiers.

On older engines, a heavier base-weight oil makes a bit of sense in that the earlier air-cooled engines had wider tolerances built into them to allow for contraction and expansion of the metal as operating conditions changed. The heavier stuff helped keep oil pressure stable and didn’t burn off as quickly as lighter base-weight oils. Something like Castrol’s Activ4T (mineral) is a 15W-50 product and is very suitable for ‘80s and early ‘90s superbikes like Suzuki’s GS1000 range.

When Yamaha had a world launch of its R6 at Phillip Island around the turn of the millennium, I snooped around the back of the pits and was interested to note it was using Castrol mineral oil. Clearly Yamaha thought it was good enough for its high-stress 600 Four.

Semi-synthetic and full-synthetic products need less in the way of viscosity modifiers due to a naturally higher viscosity index. It’s one reason synthetic oils claim a longer service life.

Race pace

A trap for young players is to assume racing oils are better than standard oils. Most manufacturers will offer a ‘racing’ oil. It will have a light base-weight to reduce what’s called parasitic drag. You know how it’s easier to walk through water than through mud? Same thing: light oil won’t drag on moving components as much as heavier oil.

Racing oil will also have a customized additives package to allow it to offer maximum protection but not for very long. No proper race bike will do two meetings with the same oil and even some of the more general racing oils specify no more than 1000km between changes.

Unless you’re actually racing, don’t use the racing oils.

Alphabet soup

While is fun to delve into the language of oil boffins, there are really only a few things you need to know and understand.

There are two main standards applied to oils: API (American Petroleum Institute) and JASO (Japanese Automotive Standards Organisation). API has been around for years and has a variety of ‘groups’ in which various lubricating oils can be categorised with synthetics starting in group 111 and running through Polyalphaolefin (PAOs) to Group V which are Esters. The latter two groups are the higher standard of synthetics and are generally expensive so are often used to fortify other base stocks rather than form the base stock themselves.

API deals mostly with automotive classifications other than motorcycles which has created some conflict over time. Engine oils for four-wheelers have trended towards lower viscosity and lower friction to achieve better fuel economy. This has been driven by government legislation in large parts of the world but doesn’t really take into consideration the specific needs of motorcycles. These new oils can certainly cause clutch slippage and pitting wear in the gearbox and muddy the water in terms of working out the quality of oils suitable for bikes.

It’s logical to assume, for example, that an oil rated SL will be better than the SG before it but in order to meet the changing needs of cars with catalytic converters, it may contain less of some additives like phosphorus and may have more friction modifiers, making it actually less suitable for bikes than earlier classifications.

The Japanese took the bull by the horns in developing its own set of tests specifically aimed at motorcycles. Its classifications relevant to bikes include MA, MA1 and MA2.

The owners’ manual for your (modern) bike will provide you with both an API classification and a JASO classification for a recommended oil and both standards should be met if possible.

The Royal Enfield Himalayan manual, for example, specifies SAE (Society of Automotive Engineers – but don’t worry about that) 15W-50 of an API SL grade along with JASO MA2.

That’s a high-spec combination for RE’s new engine although it doesn’t specify the oil be synthetic. Castrol Power1 4T 10W-40 would do the job admirably, as would Penrite semi-synthetic MC4ST but so, ironically, would Castrol’s mineral-based Activ4T 15W-50.

What the manufacturer recommends should be matched with what’s on the label of the oil container but there’s plenty of room to experiment with brands.

The truth about oil is out there

How do we know if what’s on the label is actually the truth about what’s in the bottle? For an oil to be actually tested by JASO is very, very expensive. If it’s tested, the packaging can carry a genuine JASO logo. JASO reserves the right to pick samples of the oil later at random off retail shelves and test it again to make sure it consistently complies.

What usually happens is there is an industry understanding of how to make, for example, a JASO MA2 standard oil. It will have the right base stock and the right additives package so that if it was actually tested, it would pass. Castrol, for example, says on its Activ4T label that the oil, “exceeds the requirements of API SG and JASO MA2 standards”.

In the end, it gets down to trust. A company like Castrol has too much to lose to end up in court over the quality of its oil. It has happened, though. Mobil brought a complaint against Castrol in 1999 for changing the base oil in its Syntec product from Group 1V to Group 111. Castrol was still using Group 1V PAOs but on a base stock Mobil said wasn’t really synthetic and shouldn’t be labeled that way. Castrol ended up winning and it resulted in cheaper oil with the performance of synthetic.

How can you actually test an oil to see if it is what it says on the label? Spectrographic analysis will do it. The oil sample is broken down into the wavelengths of light emitted from each component so percentages of additives can be determined. It’s used occasionally in court cases where an expensive engine has failed and the owner blames the lubricant, but it’s not a cheap process.

What about Black&Gold oil from the supermarket? It has numbers all over it and says it meets certain standards but why does it only cost $15 when branded oils cost $50? It goes without saying that the supermarkets that stock it don’t make it themselves and it’s cheap because it would have the minimum additives necessary to meet the API standard it claims. Expect the additives to exhaust themselves earlier than ‘name’ brands but there’s no reason to think if you use it in the family truckster and change it more than regularly that it won’t do its job. Don’t use it in your bikes, though.

If you don’t have your owners’ handbook, a quick blat on the interweb will tell you what oil specification your bike’s manufacturer recommends for your particular model. Trusted oil brands will give you peace of mind even though you pay a little extra for the privilege.

Which oil the experts use

Brian Rix (international bike traveler, author and Road Rider magazine contributor)
Bike: BMW R1200GS (330,000km) – Shell Advance 15W-50 mineral.

Guy Allen (AllMoto editor and man-about-town with 30 motorcycles)
Bike: multiple – Penrite is the default setting as it has an oil for just about everything.

Spannerman (Selected bikes from his shed)
Bike: 1980 Suzuki GS1000G – Castrol Activ4T 15W-50 or Penrite MC4ST 10W40
Bike: 1997 Honda VTR1000 – ECSTAR R7000 10W-40 full synthetic
Bike: 1976 BMW R60/6 – Castrol GTX 15W-40 (engine can use friction-modified car oil as clutch is separate)

Greg Leech (Director INFO MOTO and ex-editor of everything else)
Bike: 2019 BMW S 1000 XR – Castrol Power 5W-40

Alec Simpson (Ducati racer and international traveler)
Bike: Ducati MHR – Castrol RX Mono DD 50W

Cut the manufacturers’ recommended service intervals by a third if you:

• Only ride less than five kilometres per trip
• Spend extended time close to the redline
• Ride in dusty conditions on lots of dirt roads
• Ride constantly in stop/start traffic
• Only ride your bike irregularly