20w50...to thick?

This is not a "what brand" question but what weight question. I'm riding in the warmer climates so thinker oil seems more logical. For my 250's and my 310 I run 20w50 and so far so good. All the parts look good and clean. However it seams that my '12 wr450 isn't turning near the rpms as my smaller bikes do. I'm not wondering if it might be better to go to 10w40 or 15w oil instead.

What weight oil are you guys using?

I use 10w40 bel-ray mineral 4t oil in my WR450 year round. I ride in temps from 30 - 100 degrees normally. Also run 10w40 penn green in my race car no problem.   

I've never found it to matter.

It doesn't matter unless you're in really cold climates

Usually the manual has some kind of temp / viscosity chart, might see if it shows 20w50 as an option? filter bypass is usually a concern with too thick oil, when cold, and also at high rpms. Then there is the subject of ring function at different viscosity's which is a whole other topic.  

[...] it seams that my '12 wr450 isn't turning near the rpms as my smaller bikes do.


And it never will.  For one thing, the WR is rev limited 2000 RPM lower.  For another, it's built to a completely different tuning philosophy.


But either way, and even for your 250F's, 10w-40 is plenty for your bikes right up to the point where outdoor ambient temps exceed 100 degrees.  That assumes oil in good condition, obviously, and you have to remember that the first thing that will most likely "fail" in any oil used in a motorcycle that shares engine oil with its transmission is the part of the additive package that makes that 10 wt base oil act like its really a 40 wt when it's hot.  Keep it changed, and use something made for the job.


The manual for your bike actually specifies 10w-40 up to 114 degrees ambient temps.  I'm a little uncomfortable with that, so I switch to 20w-50 for the 3-4 hottest months in southern SoCal.  The important point is that the manual recommends using 20w-50 only when temperatures are at least higher than 40 degrees (F), while a 10w-40 is still OK down to 30.


In a four-stroke, it is more important to have a high volume of oil flow to the lubricated parts than it is to to have high pressure or to have a "thick" oil.  The protection provided by engine oil is not tied to its viscosity except where the viscosity is extremely different, and an oil that flows through the system faster will protect the engine better than one that moves more slowly but is thicker.  For the bulk of your use, I would recommend using the 10w-40. 

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