What about engine oil?

What about engine oil?

Viscosity must be the most important characteristic of engine oil. But what is viscosity? Imagine it as he resistance of a fluid against flowing.

  • The “thicker” a fluid is, the more it resists against flowing. We call this a high viscous product.
  • The “thinner” a fluid is, the easier it flows and we call this a low viscous product.

High viscous products are “thick”. This is also explained as if their molecules take more space. In other words, a high viscous product needs more place to flow. In our engine this means that the tolerances have to be bigger.

Now, let’s speak about tolerances. This is something we cannot influence. Tolerances cannot be changed, they are part of the design, the engineering of the engine. It is up to the developers of the engine to set the tolerances. Setting the tolerances, they also pinpoint a fixed viscosity for the lubricating oil. SAE (Society of Automotive Engineers) classified the engine oils according to their viscosity. They called it SAE GRADES.

Viscosity is changing in function of temperature. The temperature of our engine is changing constant.  There is a big gap between the start-up and cruising temperature.  Also the environmental temperature has an influence. As we do not want to change oil several times during a ride, we add Viscosity Index improvers. Thus, multigrade oil is born. These multigrade oils (15W50 for example) show an acceptable viscosity at different temperatures.

First point set:  Our engine needs a Multigrade Oil. This way it performs well at different temperatures. The viscosity is set by the manufacturer.

  • For the old Bullet 350 & 500 engines: SAE 20W50
  • For the new Bullet 500 EFI engines: SAE 15W50

Besides lubricating, oil has to cool and to keep an engine clean. The oil has to perform. API (American Petroleum institute) test oils for their performance and give them a category. ​The symbols are “S” for spark ignition (gasoline engines). “C” stands for compression ignition (diesels). Early categories as SA do not perform for modern engines anymore.  Engines evolve and the oils do upgrade. The previous categories become obsolete. Current categories are SN, SM, SL and SJ. Unfortunately  API has abandoned the motorcycle oils (for wet clutches) as from category SJ. API SJ oils and newer refer to be specific for automobile use.

Second point set: We need oil of an API category older than SF or SG. If not available anymore, we need to take an oil category API SJ- approved for motorcycles.

  • For the old Bullet 350 & 500 engines: –
  • For the new Bullet 500 EFI engines: API SL

For the new EFI engines, Royal Enfield specifies an API SL grade.  Yet, be sure it mentions to be an oil for motorcycles.

Specific relevant to motorcycles is the JASO standard (T904) (Japanese Automotive Standard Organization). JASO MA and MA2 standards are designed to distinguish motorcycle oil for wet clutches.

Third point set: To coop with our wet clutches, we need oil performing against the JASO MA or JASO MA2 standard.

  • For the old Bullet 350 & 500 engines: –
  • For the new Bullet 500 EFI engines: JASO MA

Synthetic or Mineral oil?

Often synthetic oils is considered to be “better” compared to the known mineral oils. This statement doesn’t make sense. Mineral oils are as good as synthetic ones. They are just different. Depending on your requirements, you will have to choose.

Mineral oils tend to oxidize after some time. They become acid and loose the lubricating capability. Mineral oils also have a big viscosity change between cold and warm circumstances. But: they perform fantastic if you let your engine the time to warm up before a ride. They fulfil the demands if you exchange them on time (Exchange them after 3000 km or 6 months)

Synthetic oils tend to have a much more stable viscosity over a wide temperature range. They also are not that sensitive to oxidation.

Fourth point set: you can choose for a mineral oil. But respect regular exchange intervals and warm up time. If you keep the oil in for a longer period or operate the engine over a wide temperature range, take synthetic oil.


  • For the old Bullet 350 & 500 engines: SAE 20W50 – API SH – JASO MA
  • For the new Bullet 500 EFI engines: SAE 15W50 – API SL – JASO MA

Possible commerecial oils:

  • ELF Moto Road 15W50 – API SJ – JASO MA2
  • Eurol® Sportbike 15W-50 Full Synthetic – API SH – JASO MA2
  • Eurol®Sport Touring 20W-50 Ester blend – API SG – JASO MA2
  • Shell Advance 4 – 15W50 – API SG _ JASO MA

One thought on “What about engine oil?

  1. Thank you for giving such a detailed explanation. I live in US and it’s been hard to find engine but I think now I will be able to find it I have 2012 royal Enfield 500.


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