We try to answer the commonest question – “Which Engine Oil should you use?”.

Note: This “Which Engine Oil” is an old article which was published long back. Since, we have been receiving a lot of queries on engine oils of late, we are bumping it up for all of you who have missed reading it.

I have been encountering a lot of confusion among bikers with respect to the different engine oil recommendations from manufacturers for their respective vehicles. This article is prepared to make a layman understand what does different grading signify and its implications on our engines in a very simple language.

Whenever you buy a new bike, it’s mentioned in your owners manual that you should use only the recommended “xWy” (for eg 20W-40, 10W30 etc) grade of engine oil. Now what is this xWy and what precautions should I take to ensure I am doing the right thing.

Which Engine Oil Let us understand letter by letter.

  • The first letter ‘x’ stands for the viscosity number of oil when the engine is cold. For the sake of understanding let us take this colder temperature as 0 degrees Celcius
  • The letter in between ie ‘W’, stands for winter
  • The third letter ‘y’ stands for the viscosity number of oil at engine operating temperature. For the sake of understanding take this operating temperature as 100 degree Celcius.

Viscosity, simply put, is nothing but the thickness of a liquid. Higher this number, thicker is that liquid and obviously more resistant to flow across. And thinner the liquid easier does it flow across.

For example, Kissan’s tomato ketchup is thicker than water. So ketchup would have a higher viscosity number (or viscosity index) and water would have a lower viscosity number. When you put a drop of each on a table and try to slide, you would notice that water easily flows across whereas ketchup takes its own little time to slide down. The same principle is applicable to engine oils.

Understanding x & y

As soon as we crank our engines, the internal temperature is generally cooler (as compared to an instant when the engine is running) and there are a lot of internal engine parts which move and rough up with each other. Hence the oil is required to quickly move up to all those parts and clung on them for better protection. And this is where the ‘x’ (first letter) comes to play. The lower the number, easier it would be for it to flow across and cover up the roughing engine parts. Hence a 5w50 engine oil would be better than a 20w50 engine oil here.

Let’s turn our attention to the second letter ‘y’. Consider an example when you have been riding for an hour continuously on your bike in scorching summer at stop and go city traffic. Do you understand the amount of heat generated and the temperature inside the engine at this instant? And we all know that under higher temperature liquids have this property of becoming thinner. So we need a thicker oil, don’t we?

Which Engine Oil

This is where the ‘y’ figure comes into play. This figure should be higher enough to accommodate the ‘thinning’ of the engine oil at rising temperatures and ensure that the engine oil remains ‘thick enough’ to protect the engine at these burning temperatures. If this is not taken care of, engine oil would become thinner (like water) and would not clung to the walls of engine and loose its property of proper lubrication.

An Example

For better understanding, let us take an example: I and one of my friend start together on two Pulsar 220s. I am using xW50 oil and my friend is using xW40 oil (forget about what the manufacturer has recommended for an instant). We ride on same roads and under similar conditions. After an hour, which engine oil do you think would be more effective? Yes, owing to its higher viscosity (thickness) at engine operating temperatures (ie the temperature that time), my xW50 engine oil would be protecting my engine more effectively than my friends’.

So, Which Engine Oil?

I hope you have understood till here. However, I have a few more pointers to make which even if you do not understand completely right now, you will gradually get them.

    • You can use a higher grade engine oil (higher ‘y’) than the recommended if your kind of riding includes more ‘frying’ up of the engine. For eg: You can use xW50 even if your recommended grade is Xw40 in case you ride a lot in city traffic and your place is a lot hotter or you like (sensibly) ripping the bike more often than not.
  • An exception to above relaxation would be not to go to extremes. Since a thicker oil would be difficult to push the engine around.
  • Do not go below this figure of ‘y’ ie. You should not use any engine oil with a lower ‘y’ rating. If your manufacturer recommends engine oil of grade xW40, you should not use any oil below 40. An oil of xW30 would be ineffective in providing proper lubrication to your engine at higher temperatures.
  • The first figure ‘x’ matters a lot at places which are colder and have freezing temperatures generally. In our kind of relatively hotter climates where winter temperatures generally do not go extremely harsh, ‘x’ could vary. So, if your manufacturer advises you a 20Wy, you can use other figures as well as far as they are lower than 20.

We generally prefer and suggest Motul Engine Oils over other oils available in the market as we have had good experiences with them.

In case you still have confusions, you can send us messages at our Official Facebook page. And if you like the info, do not forget to share it across to your friends.

Also Check Out List of all Informative Articles

Click To Expand


  1. superb man, I had never heard that.
    Just realized why my Hunk gave lower mileage as low as 25-30kmpl when i had used Castrol 20W40 and how it improved to around 40kmpl when i used Gulf 10W30(which was recommended by manufacturer). Also felt sorry for my bike which showed lower pickup and i pushed it even harder to attain what it used to be earlier.
    Also i wanted to know anout synthetic, semi-syntheti and organic engine oils.
    Can i use synthetic and what effect will it have on the bike ?

  2. Please tell how much amount of oil we should add in the engine? I take my bike(Hero Splendor) to the Service center and they fill in 800ml in it, while I have heard that it should be 900ml! So, please clear this confusion pls…

    • engine oil req . Based on engine capacity oil quantity is seen i.e. 100cc=900ml,125cc-180cc=1000ml,above 180cc=1200ml. ok

  3. Very very important and useful article for bike riders. One must seriously read and follow the instructions as laid down in this article and also educate others.
    Thanks to Bike Advice as also to Saad Khan for his contribution in this article.


  4. Amazing article sir 🙂 🙂
    Truly informative 🙂
    Could you please specify if the choice of oil affects the mileage ??
    Also does any wear n tear increase if u use oil not specified but higher ‘y ‘ than my actual oil?

  5. i have a tvs star city and my bike mileage is good because i know the how to improve more mileage in bike every 1500km i removed my oil timely thats why it will give good mileage.if you do the same thing then you can improve your engine efficiency……………..the first thing is oil changing in ur bike the 2nd thing is you do the service.

  6. very informative n essential article for….. the common sence of bike owners…..who mostly depend on mechanic’s choice…….thnx

  7. I want to more about synthetic engine oil ? would purchasing it which is very expensive as compared to other oils avaliable in the market worth it ? I drive usually on highway NH-58 which is quite smooth .please recommend me oil which is best suitable for my bikes apache 180 & yamaha fazer .

  8. its explaind very easy n clear way!!! Thanx for clearing my confusion too…
    I use veedol swift 10w40 eng. Oil for my h.h. Ambition!! It works very smooth,, like evry day a new n powerful engine!! thanx!

  9. good one, it would have been better if you also suggest the engine oils for common bikes like pulsar, apache, cbz, etc., if feasible.

  10. Hi bro

    You have shared a mind blowing post with us.Its really very informative & got a lot of things to learned after reading the same…….
    keep on sharing buddy……….

    Luv u deepak for this

  11. I have a doubt , when we give our bike in service center and demanding an oil change whether the service guys drain away the old engine oil and fill new or just top up the oil with out draining.

    • All service centers usually drain old oil but there is an exception in case of some service centers might top it up and charge you full cost of an oil can. Its even in the service Manuel to top up oil at 2k and change it at 6k. It depends on the practice carried out by SOME service centers. If you have such doubts don’t visit SC’s, find a good private mechanic its good for your bike’s sake.

  12. thanks the technical information…. now, it answers my long time question about the right engine oil grade that is necessary to my bike/s.
    more wisdom… God bless…

  13. Very informative and impressive article……like it very much….. But i have one doubt. As I am using Yamaha R15 which likes to run at higher RPM figures…. what grade of engine oil would be suitable for it as i also go on journeys of several hours at a time???
    Please somebody help me about……

  14. thanks for your kind information i use a 20w50 grade oil but i didnt what that mean i ride a pulsar 180 is it ok for that my gear gets hard often please advice.

  15. / if your manufacturer advises you a 20Wy, you can use other figures as well as far as they are lower than 20./ This kind of doesn’t look right – there is difference in viscosity of oil 15w and 20w but if 20 wis recomended then 15 W means more viscous or less viscous? if its less viscous then not going to bear the engine load at normal temperature even. or I am understanding something wrong here.

  16. The information which is mentioned, is very easy to understand, and it is a marvelous. This helps us a lot and it gives a total knowledge in this regards.

    thanks for the same with warm regards,

  17. Thank you..I was looking to change my engine oil and this post was very informative.

    What is the different b/w semi-synthetic and fully synthetic? My mechanic advised that semi-synthetic is better than fully synth for my pulsar 220..What is your opinion.


  18. I have a question Mr. Khan. I’ using Honda Unicorn. Presently using the Castrol Engine oil according to the grade. Is this the correct blend or can i even use the greater blend of engine oil for my machine. Please answer and Thanks in advance

    • Did not understand your question completely…
      However, if you are talking about ‘quality’..then we do have better quality of engine oils than Castrol..

  19. Excellent informative article decribed and simplified for lay people like me. I would like to have some more knowledge regarding Eco-Friendly Lubricants. What make them eco-friendly first off? Also what would be the best oil for a high drain interval?

  20. Superb article. yo have explained in plain and easy english. but please clarify the doubt which was asked by biker x. what is eco friendly lubricants and which oil is best for long drain intervals.

  21. thanks a lot. but if you could post it in bangla version that would be more efficient and understandable. again thanks.

    • Saberul, we, unfortunately do not know Bangla.. 🙁
      We suggest you to please use translation tools. Or you can simply translate it through Google Chrome…

  22. Hello Saad,

    I would like to know what is the company recommended engine grade oil for Yamaha RX 100/135/G/Z. I am presently using Motul 5100 15W50, it is a good oil but I find that it is very thick and stresses the engine out. I come from a cold place with minimum temperatures touching 0 deg celcius in winter and maximum temperatures in SUmmer are 26-28 deg celcius. Will Motul 5W30 suit my bike?

  23. I’m in loss of words for praising bike advice for this article .. I mean who gives such a perfectly fine piece of information with metaphorical examples like kissan ketchup .. ! ? Seriously sensible stuff … cheers to bike advice …

  24. My royal enfield classic 350 tends to overheat a lot in short while…so motul 7100 20w50 or 300v 15w 50 to reduce heating …pls help

  25. Nice explains, can u clarify that while starting the bike if we use 15(X) will help us easer startup than 20(X) and after engine get heated 50(y) will be good than 40(y). Am I correct?? Also both variations are full synthetic oil is it? @Depajyiti

    • because most MOTUL oils are of good quality and synthetic, you can go for shell synthetic ones too. They are also good.

  26. Hi, iam using old ct100 bajaj bike which is the best combination for my bike, can i use 15w50 or 10w50 or 20w50 or ?????????? pls suggest and thanks.

    iam from Bidar Karnataka, INDIA


Please enter your comment!
Please enter your name here