oil weight

   I have 3 bikes: Honda Rebel 250, Yamaha Vino 125, and Honda
Metropolitan 50cc.

  The Honda bikes both take 10W-40.  The Yamaha book says you use
20W-40 when the temperature is above 94F, and otherwise use 10W-30.  In
the interests of simplifying, is it OK to use 10W-40 (or 5W-40) on all
the bikes?  Am I going to lose any power on the Yamaha if I go to a
thicker oil in the winter?  This might be academic for something 250cc
or larger, but the Yamaha is only 11 horsepower and could potentially
spend alot of time at higher RPM's than say, a larger motorcycle.

 
Magnulus wrote:

I would, but it depends on your climate. It never gets real cold here
in NorCal. I run 15W50 in all my bikes. The Kawi and 4 of the Hondas
calls for 10W40, one calls for straight30. The Harley calls for 20W50.
I wouldn't run the Japanese bikes with the 15 weight if I ever planned
on riding them below freezing.

As for loss of HP? You may lose a teeny tiny bit of HP, but I doubt
you'd ever notice it...
The smaller of the two numbers in a multi vis oil is the 'base stock'
so you're really not going any thicker on the Yamaha.  Well, unless
you're torturing it, and then the higher number *may* be better for it
as the larger number means when the oil is extremely (260 degrees F)
hot it won't thin out any more than a straight 30 or 40 wieght oil
would at that extreme temp.
--
Rayvan

 Magnulus wrote:

My bike has a really hard time starting in the winter if I use summer
weight oil.  It's too thick when cold.

 
timeOday wrote:

What's the viscosity of the "summer weight oil" vs winter weight?
--
Rayvan

 Rayvan wrote:

20w/40 vs my usual 10w/30