I wrote that pretty poorly, didn't I? You're right, in a multi weight oil
designation the first number is the thin side, with the right number being the
thick side. So a 15-40 weight oil is supposed to be 15 weight when its cold,
and 40 weight once its heated up, very losely described.
What I was trying to say (and did so rather poorly) had to do with the effects
of those weights under specific conditions, namely summer heat.
The 15 (cold pour) side of a 15-40 weight oil can make it a bit thick to pump
on a cold morning. Not the end of the world, just something to be aware of.
Live down south and it's fine. But if your summers are in Michigan, it may be
a bit too heavy, and 10 could be better. As in a 10-40, not a 15-40.
The 40 (hot pour) side of a 15-40 weight oil is right in the middle of most
recomendations for viscosity. A 50 weight here (x-50) is almost always
overkill. A 30 weight (x-30), while common in modern engines, can be pushing
it for an older worn engine. Have a situation where the engine will be
running hot (inadequate cooling, hard work, extremely hot environment) and that
50 weight may not be overkill.
Hopefully that time I managed to make a bit more sense. :-)
And yes, I am aware of the break down problems with 10-40 due to the large span
of viscosities. I was ignoring it for the moment. Personally, I suspect this
problem is a bit overstated, particularly as it relates to cars like a Spitfire.
>>> "Keith R. Stewart" <kstewart@wwdc.com> 05/31 6:43 AM >>>
Nolan Penney stated:
> 15-40 too thin for summer? That's a new one on me. The 15 side of the
equation is so thick it's usually not recommended for winter. It requires
summer heat to be easily pumpable on a chilly morning. 40 weight is not
exactly heavy oil, but it's not thin either. Unless you're cooking yourself
in Texas heat or something, the 40 weight side of the spread is quite
adeqate.
Isn't it the other way around? 15 weight is the thinner viscosity. In my
Spitfire and TR4, I run 40 or 50 weight in the summer because it is far
thicker. When the TR4 was my everyday car, ISTR using 20 weight in the
winter because it was thinner.
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