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Hi guys, probably a stupid question here, but I figure you can never be too safe. I have some Motorex 15w-50 from my 2010 KTM 250 XC (which I sold) and I was wondering if it would be okay to run in my 2014 KTM 350 XC-F which calls for Motorex 10w-50? What would be the side effects of running a 15w-50 instead of a 10w-50?

Also, if you have any suggestions of good oil to run, please feel free to recommend it and give your reasons why.

Thanks guys.

(Attached is my 350)


Edited by MotoXRacer_19
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Beautiful bike, congrats.

The first number is the viscosity at cold start, 10 is thinner than 15. The second number is the viscosity index at operating temps, so at temp 50 = 50 = the same. A 10w-50 will flow better than a 15w-50 at initial start up, however both should flow equally at engine operating temperature.

The only reason that I would caution running the 15w-50 over the 10w-50 is if you plan on starting the bike during this winter time weather and jumping on and riding right away without a warm up time (This is not recommended at any time of the year with any oil).  It may not do any damage at all, but it will not flow as easy until it reaches closer to operating temperatures comparatively.


Edited by Decreasing Dave
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  • 2 weeks later...

As others already covered, 15w is just thicker when cold.  Don't use it when it is cold out, or warm up the bike in the garage?

With the cams being journal bearings, and some reported failures out there with that plastic breather tube, I would blend the 15w-50 into your truck or something else, and buy the correct viscosity for the 350.

I bought this case of 10w50 when it was on sale for $35 (seems to be every few months), but it's still not that expensive.


Edited by mbrick
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