Peter Landy wrote:
> This is the part where I am a bit confused. I would imagine all parts of
> a cold engine would contract or shrink more or less equally. So then if
> this is true how could additional clearance develop, internally, when
> the engine is ice cold?
Well, couple of factors. One is that different parts are
different metals, so the expansion rates are different. The
other is that some parts get hotter, the piston is much hotter
than the block itself.
Unsure which way that makes it all go, but those are the
factors at hand.
> Viscosity is supposed to be the measure of resistance to fluid movement.
> It was my impression that, for example, a SAE 10W-40 oil will act like a
> SAE 10W oil when cold, but a SAE 40 oil when hot. Therefore the lower
> the viscosity, the thinner the fluid.
Not quite...
It acts like a "cold 10W" when cold, and a "hot 40W" when hot.
It's still thinner at higher temperatures, it's just that
it's only as thin as a 40W oil at high temperatures. This is
fancy because it doesn't get as thick as 40W oil when cold,
it only gets as thick as 10W oil at equally cold temperatures.
The idea is you can use oil that isn't molasses at startup
and isn't water at temperature either. A choice straight oils
won't give you, with straight oil you choose one or the other.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
|