Paul:
To get that large a viscosity range, the manufacturer adds more
viscositizer. Viscositizer has inferior lubricating properties compared
to the base stock, so the wider the viscosity range, the worse the
lubricating properties.
Consumer reports recommended a viscosity range no greater than
25, and stated that a range of 20 was to be preferred. This was many
years ago, and I am sure that technology has improved since then. Never
the less, I stick to 10W/30. This is within the range of recommended
viscosities in the owners manual (as I recall, but I am bit fuzzy on
that point).
The lighter oils circulate more quickly on startup when most of
the wear occurs. Once you have oil circulating the wear drops sharply,
to the point where for the average motorist the lighter viscosities will
result in improved engine life even though the ultimate film shear
strength of the lower vis oils is inferior.
Trust me, the thinking that you need higher oil pressure at high
RPMs is just plain obsolete. Higher oil pressure reduces fuel economy
because the oil pump works harder to pump the oil, and it gives no wear
benefit. The lighter vis oils reduce wear AND improve economy - hence
they are the recommended oils for modern engines.
Us old timers with oil pressure gauges get twitchy when the oil
pressure is not at 75PSI, so we tend to favor the higher weight oils, to
the detriment of our motors.
Vance
-----Original Message-----
From: mgs-bounces@autox.team.net [mailto:mgs-bounces@autox.team.net] On
Behalf Of Paul Hunt
Sent: Friday, August 27, 2010 12:51 AM
To: Bert Palte; mgs@autox.team.net
Subject: Re: [Mgs] OIL
Castrol GTX for example stopped 20W/50 in the UK many years ago - they
made
it 15W/50 instead which was an improvement. Then a few years ago they
changed that to 15W/40, which showed up as lower oil pressure on my V8
but
not the roadster. You can still get 20W/50 here, but only from the
lesser
names and specialist places.
PaulH.
----- Original Message -----
> Yeah, 20W50 is what I've been using over the last decades for my LBCs.
>
> An now, I find that, over here, it i gettin more and more difficult
to
> get that grade....
_______________________________________________
Mgs@autox.team.net
Donate: http://www.team.net/donate.html
Suggested annual donation $12.75
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
|