Motorcycle Engine Oil Frequently Asked Questions (FAQ’s / FAQs)

Motorcycle Engine Oil Frequently Asked Questions (FAQ’s / FAQs)

See below for Castrol links and their Motorcycle Oil Q&A videos

See also: BMW / Castrol Engine Oil – Q&A

See also: BMW R1200GS Alternative Engine Oils & Other FAQ

So, here we go again, one of the most (if not the most…..tyres maybe?!) talked about subjects on pretty much any motorcycle online community or forum – all those engine oil related questions!
What do all the numbers on the oil container mean (20W/50 or 10W40 etc, viscosity, API classification and so on)? ~ Are synthetic oils better? (better than mineral oils or semi-synthetic oils?) ~ Is Castrol (or any other brand) better than Silkolene (or any other brand)? ~ Can I use car engine oil in my motorcycle?…….and all the many other questions about motorcycle engine oils.

I’ve started this page (23Mar2010) as a result of coming across Castrol’s motorcycle oil dedicated website (see below for  Castrol links and their Motorcycle Oil Q&A videos) and will as time permits add more information. For now here’s a few links to other web sites/pages I’ve found via Google searches:

Opie Oils – Motorcycle Oils Technical Info
UK oil supplier – their resource of information covering various aspects of the products they sell and vehicles they are designed for. Oil Specifications – Manufacturers – Rants & Raves – Technical Articles – Glossary of terms – Oil addatives – Synthetics myths… and lots more.

Mobil1 FAQs for Motorcycle Oils

Bob Is The Oil Guy (BITOG) began in May 2002 with a handful of participants and now the oil forums have over 31,000 registered members. And we have well-respected tribologists, chemists, and oil analysis professionals who regularly participate and contribute their knowledge and expertise. Unlike most private motor oil web sites, Bob Is The Oil Guy is not about selling you something. It’s about educating you so you can make informed decisions about the life blood of your engine: motor oil.

…and if you really want to dig deep:
A Study of Motorcycle Oils (Second Edition) by AmsOil (they state “There is no hype, no sales pitch, just facts. Never before has so much information on motorcycle oils been delivered in one easy-to-understand source.” but AmsOil commissioned the report so a cynic may suspect some bias?!


 And now, from Castrol….

Castrol motorcycle oils dedicated web site:
Check out for lots of information and advice on motorcycle engine oils – some specific to the Castrol brand but a lot of useful ‘generic’ advice and information as well. I found the section on motorcycle oil R&D (Research and Development) very interesting.
Castrol Motorcycle Oils product range:

Expert answers from Castrol (Castrol Rider Support:

A series of short but informative videos from Castrol in response to frequently asked questions on the subject of motorcycle engine oil: Motorcycle Engine Oil Q&A (Questions and Answers)

  1. Can I use a car engine oil in a motorcycle?

Car oils are not designed with the high power density of modern motorcycles in mind. Neither are they tested to be compatible for use with wet clutches and highly loaded gears that you find in modern motorcycles. 

2. …and what if I have a dry clutch? (or in the case of the R1200 BMW Boxer engines e.g. R1200GS a seperate gearbox / transmission i.e. dearbox/clutch seperate from engine oil)

Even in a dry clutch application the engine oil still has to lubricate and protect the gearbox (na to BMW Boxer engines, R1200 etc) and provide high temperature protection which a car engine oil may not provide.

3. What is the function of engine oil in a motorcycle?

The engine oil serves to lubricate key components, reduce wear and remove heat from the engine and clutch.

4. What are the most critical areas where the oil flows?

In most cases the critical engine areas are the piston assembly, bearings and valve train, coupled with the need (na to BMW, see previous comments) to protect the gearbox and lubricate and cool the clutch.

5. What’s the function of the oil filter?

The oil filter works to trap foreign particles and debris introduced into the oil by normal riding. These particles can lead to engine damage, while a blocked filter may lead to oil starvation and ultimately engine failure.

6. Can an engine oil improve performance or is it only for engine protection? 

Yes, by reducing internal friction and drag the oil can improve engine efficiency and therefore enhance engine performance. In most cases this is achieved through the use of low viscosity, friction optimised oils.

7. Why do some OEM’s recommend low viscosity oil?

It reflects the need to produce more fuel efficient engines, coupled with improved manufacturing processes.

8. What does a Moto GP engine use as oil?

The oils are very different to road oils and tailored specifically to the Moto GP engine. That said, the techniques used for developing high performance Moto GP oils are used for our Power 1 oils.

9. Can I use the same oil at extreme external temperatures?

Yes, with the use of high performance base oils, in multi-grade engine oils, we can ensure that the oil flows when cold and will not evaporate or burn away when subjected to high temperature operation.

10. Can I use a track day oil for road driving?

It’s not advisable as track day oils are designed specifically for enhancing performance over short periods of time and may not be suitable for long drain use.

11. What does ‘deposit’ mean?

Deposits are a by-product of combustion and are usually carbon formation on components such as pistons. Over time this can lead to issues such as lack of compression.

12. What effect can a very thick oil have on the engine/gearbox/clutch?

Modern engines are designed around the use of thinner oils. As a result, the use of a thicker oil may compromise ultimate performance of your engine.

Follow the link below for more videos from Castrol including: Castrol Motorcycle Engine Oil – R&D Video, Castrol Motorcycle Engine Oil – Engine Tests Video and Castrol Motorcycle Engine Oil – Field Tests Video: