Shearing/Viscocity Question ?

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Just curious as to what has more effect on shearing/viscosity break down. Would a 20w-50 oil viscosity break down more from heat (say normal heat) in a air cooled H-D motor application or from a l/c shared sump application of a metric type bike? Sorry if dumb question... Thx
 
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My guess would be a shared sump application. I know that my shared sump racing engines will shear many oils one grade lower in a matter of an hour or so. Never owed a Harley though.
 
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My BMW K75C has NO Tranny gears in the crankcase sump and it will cut all the oils I have used in the last 26years down one grade or almost 2 grades on 20W-50 oils. There are gears driving the timing chain, oil pump, balance shaft and output shaft though.
 
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even the not worth buying oil can handle heat. what shows the real differences is if they shear and by how much! as an example castrol gtx 20w50 sheared to a high 30wt in my tests in under 3hrs. while valvoline vr1 20w50 remained a 50wt. and both had flash points over 425 as tested by the stoners. which would you trust for more than 3hrs? or 30? or 300? steve
 
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