This age-old question about oils doesn’t have an easy answer.
However, your motorcycle manual will specify a particular oil and it is prudent to adhere strictly to that. But usually the manual only provides specifications of viscosity/weight and service classifications, not the origin or the manufacturer.
Synthetic oils are manmade, consistent and devoid of contaminants, while mineral oils come from the ground and, although being refined, can contain some contaminants.
But does that mean you should only use synthetic oils? Not really. The mineral oil refining process is very thorough. Any contaminants will be miniscule and unlikely to do damage. Besides, some synthetic oils actually use mineral oils as part of their formula.
The main advantage of mineral oils is that they are cheaper, sometimes about a quarter of the price of synthetics. Many new motorcycles are delivered with mineral oil in them. That’s not necessarily a cost-saving measure. Mineral oil actually helps the rings and pistons bed in properly during the crucial run-in stage. Synthetic oils can create a film around the bore so it doesn’t seal properly, leading to slippage and higher oil use later in the engine’s lifespan.
Mineral oils are also more suitable for older motorcycles because they are heavier or thicker and don’t leak. Owners who change to synthetic oils in older motorcycles often find they leak more.
But be aware that older bikes specify the type of oil that was available at the time they were built and those oils may not be available anymore. However current generation oils will be far better than what was originally specified for older applications.
Will an older bike benefit from an expensive synthetic oil as opposed to a current generation mineral oil? Probably not, as older engines (unless modified) are unlikely to be that highly stressed that they would benefit from a synthetic.
Will it do any harm? Providing viscosity ratings are appropriate – probably not, except to your wallet!
As for modern motorcycles, most mechanics believe synthetic oil is best, especially after the first service.
There are many advantages of synthetic oils, including the fact that they are better able to properly lubricate and tolerate the extremes the oils are subjected to in modern high-performance, high-revving engines. especially when operating in hot climates.
Synthetic oils also last longer which you will see for yourself when you drain the sump at your scheduled next service. Synthetic oil usually doesn’t form such a thick, black sludge caused by oxidation.
But don’t be alarmed if the drained oil is dirty. That’s just the oil doing its job. If it comes out looking the same as it went in, you might have a problem as it’s not doing its job.
The lower viscosity (resistance to breaking down) of synthetic oils reduces internal friction which means better efficiency, more performance and slightly higher fuel economy.
It may cost a lot more than mineral oil, but it may yield some economic returns in fuel economy, a longer-lasting engine and longer periods between oil changes. However, extending your scheduled oil change would be a false economy in the long run.
RACQ technical officer Steve Spalding advises that owners should use quality branded oil and keep to the schedule for oil and filter changes as motorcycle engines place high demands on engine oils. Air-cooled engines, in particular, place a lot of stress on the oil in hot weather and stop-start traffic conditions. (Check these tips on finding the best car oil filters.)
“In my experience, a good quality synthetic oil is a small price to pay for engine protection.
I learnt from experience when I first started riding in the late ’70s that the wrong oil can be costly. After pulling into a service station one night I filled my 250 Yamaha with auto transmission fluid instead of two stroke oil because I wasn’t paying attention, even though the oil was the typical dark red colour. Within a day of further riding the engine seized and it cost me barrels, pistons, secondhand crank and rods plus a few very late nights rebuilding the engine.”
‘And then there’s two-stroke engines: It’s fairly basic quality because it gets burnt but it’s designed to have low smoke emissions and limited combustion chamber deposits. It definitely isn’t the same as oil used in a four-stroke engine.
Also oils for wet clutches are specific to avoid the potential for clutch slip. The Japan Lubricating Oil Society (JASO) provides specifications for petrol engine oils which are particularly relevant to motorcycles and other small engines. There are specific standards for two-stroke engines, for example JASO FC or FD, and for four-stroke engines (JASO MA and MA2), such as those used in motorcycles which have a clutch and gearbox that are also lubricated by the engine oil.
If this debate about mineral versus synthetic oils leaves you scratching your head, you can always opt for the compromise of semi-synthetic oils. It’s best to speak to your mechanic about what il best suits your needs.