Oil Viscosity Change? Help?

My Motorcycle Manufacturer recommends using 20w50 oil , can I use 15w40 Viscosity?

PS : Don t Tell me to stick with what manufacturer recommends , I am just curious if I can change the Viscosity.


Other answer:

Sid Flare:
It doesn't really matter. It won't cause "flow problems." People who think there is that great a difference in the two or think it was heavily engineered are fooling themselves. I guess the person who gave feedback that you can't mix conventional and synthetic oils doesn't realize they sell semi-synthetic and that is exactly what it is. You want to run a thinner oil, go ahead. I wouldn't do it under warranty..it just gives em a reason to void a warranty. My F150 calls for 5w20. Only because it reduces resistance to the oil itself and increases MPG..but you lose some protection…I DO NOT put 5w20 in it, never have. 5w30. Take it to extremes, if you put water in a motor, it will fail. You are moving closer to water the further down you go..some oil needs to be thicker to stay in areas that spin oil off quickly.. a thicker oil doesn't move as fast and that might be a good thing, especially for high performance motors. If you have a clutch that relies on your engine oil (Like an ATV for example) a thinner oil or synthetic can actually cause clutch slippage. (Happened to me on an old Honda Big Red.. But the change you are talking about is far from that. It is just a somewhat thinner oil. Personally, I would only do that in a cooler climate in general. I just wonder what benefit you are hoping for in doing so? Remember, you oil temperature does not indicate that you don't have hot spots that are above what the machine is designed for..the motor may be able to dissipate the heat with no problem, but he hot spot can remain..from thin oil..especially in bearings and seats that sling oil around a lot. Honestly, in most engines, ANY oil is fine. Literally…as long as it is detergent..
As Robert S has said, why would you want to? It would of course depend on what bike you own & the temperature you ride it in & how you use it. Some older bikes have different recommendations for seasons…I did once read a technical article which said that 10 or 15/40 oil reached the cams much quicker on an OHC engine than 20/50, Overall, I'd stick with what the manufacturers recommend.
Candid Chris:
Some motorcylcle have built-in sensors that can detect the wrong viscosity and the motorcycle explodes at 179 miles on the odo since the change.
You can use whatever oil you wish. If I see you on the side of the road, your 179 miles is up. Wear armor pants , when it blows who knows which way your balls blow.
Don't change between conventional oil and synthetic.
They do not mix well.
There is a process to change between the two.
When doing a change over, perform an oil & filter change as usual.
Repeat with the same type of oil and a new filter within 50 miles.
Repeat once more – change the oil & filter with the same type within 50 miles.

Repeat the process if you were to change back to a different type of oil.

depends on actual motorcycle, actual temperatures encountered, actual service use. I use 15-40 in Goldwing and CM400 in summer, used 20-50 in BMW during hot summer rally runs. Use early diesel spec mostly- Delovac, sometimes Rotella. Cycle maker have the specs and standards acceptable, these meet the specs and standards, have higher zinc content, good for wet clutches. . .
You can do it. But because of bearing clearances the 50 is recommended for most air cooled engines by the engineers that designed the machine. 40 will just accelerate wear in hot weather use.
There's no law that says you can't change viscosity. DO whatever the **** you want
Tim D:
What temperatures do you intend to ride in?

Does this oil have special "cleaning" additives? In which case you will regret your choice.

Mad Mechanic:
There is a good reason why they want you to use 20w50 email them asking why then you can make an informed intelligent decision.
Ian K:
Sure, try it out.

Machine shop work is very cheap and engines are fairly easy to pull out, tear down, and rebuild!

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