I thought the article below was very informative. But maybe this is too much
information unless you're a chemical engineer.
As oils advanced in the 1960s and 1970s the British owners manuals started
recommending 20W50 in the summer.
Cheers!
Mike Mostert
Science & Technology
March 13, 2006
Volume 84, Number 11
p. 38
WHAT'S THAT STUFF?
Motor Oil
Lubricant keeps car engines from clanging apart, sparks debates on how often
it should be changed
Steve Ritter<http://pubs.acs.org/cen/staff/biosr.html>
Jose Luis Pelaez/Photodisc
Do you know where your car's dipstick is? If the answer is yes, do you recall
when you last looked at it?
In bygone days, people took time to regularly check the level of motor oil in
their car and faithfully changed the oil and filter every 3,000 miles. But
now, with new engine designs that require less maintenance, improved motor
oils, and ubiquitous 15-minute oil-change garages, many people have dropped
the routine of popping the hood to check the oil or to change it themselves.
Why motor oil? The viscous fluid spurts out of strategically located holes in
the engine or splashes off moving parts to form a thin film on the metal
surfaces. The primary role of motor oil is to reduce friction and prevent
corrosion. But oil also serves to dissipate heat and to hold in suspension the
micrometer-sized by-products of engine wear (metallic particles), combustion
(soot), and oil degradation products.
But what is motor oil? Simply put, it's about 90% paraffinic (heavy)
hydrocarbon base stock distilled from crude oil, with the remainder
constituting the "additives package," notes Dennis L. Bachelder of the
American Petroleum Institute (API)<http://www.api.org/>. The lengths of the
hydrocarbon chains vary depending on the desired properties of the oil, but
base stocks generally contain an assortment of linear and branched compounds
in the C16 to C50 range.
Base stocks are divided into five groups, Bachelder notes. Groups I-III are
basic crude oil fractions, with little extra refining done to Group I and some
cracking done for Group III. Groups IV and V are called "synthetic" oils
because they have been subjected to several synthetic refinery processes.
Group IV is made up exclusively of poly(N1-olefin)s, while Group V is a
catchall group that includes polyol esters and polyalkylene glycols, he says.
Specifications and certifications are important when it comes to motor oil,
and an array of national and international organizations set standards and
perform evaluations. API's ratings include evolving oil performance
specifications for gasoline engines (currently denoted as SM) and diesel
engines (currently CI-4).
The grades of oil are based on viscosity standards set by the Society of
Automotive Engineers (SAE)<http://www.sae.org/>. Oil grades are based on a
viscosity range at a standard temperature; the higher the viscosity, the
higher the SAE grade number. These numbers, which range from 0 to 50 or
higher, are referred to as the "weight" of motor oil.
The oil's cold-weather weight is indicated by the letter "W," meaning
"winter," as in 10W, which is gauged by the oil's viscosity at 0 B0F. The
warm-weather weight is based on the viscosity measured at 210 B0F. Oils used
to be sold mostly as single-grade products, and still are for some special
uses, such as extreme weather conditions or for racing cars. But the viscosity
range of single-grade oils is too limited for general use. That's where
multigrade oils come in.
High-molecular-weight polymers (viscosity index improvers) such as poly(methyl
methacrylate) and ethylene-propylene copolymer are added to a low-viscosity
oil base stock to create multigrade oils that work through thick and thin. At
cold temperatures, the rubberlike polymer molecules exist as balled-up coils
and don't thicken the oil significantly, Bachelder says. But at warmer
temperatures, they expand to more linear random coils to prevent oil from
thinning out too much. Thus, common multigrade monikers-indicated by two grade
numbers-are 5W-30 for colder climates (falling below 0 B0F), 10W-30 for
intermediate climates (down to 0 B0F), and 20W-50 for warmer climates (down to
32 B0F).
Now to the additives. One major class of motor oil additives is metal
phenoxides, such as RC6H4ONa, where R is an alkyl chain. These compounds play
several roles, including acting as bases to neutralize acids that form from
sulfur compounds in the oil and to prevent hydrocarbon oxidation, which can
lead to sludge formation. The phenoxides and their sulfate and carboxylate
analogs also serve as detergents to help solubilize or suspend soot and to
carry particulates to the oil filter to be removed from the oil stream.
Another key additive class is antiwear agents, such as zinc
dialkyldithiophosphates, Zn[S2P(OR)2]2, where R is a linear or branched alkyl
group. These compounds form a micrometer-thick, cross-linked barrier layer on
metal surfaces under high pressure to protect against scuffing. The zinc
compounds and various amines, such as diphenylamine, also serve as corrosion
inhibitors and antioxidants.
As with other types of consumer products, the plethora of motor oil additives
for sale at your local auto parts store vary from maybe being useful to being
snake oil. One can assume that if an additive were useful, it would already be
in the oil, or it would carry an endorsement from an oil company.
Finally, the burning question about motor oil: How often should it be changed?
Conventional wisdom has held that the oil should be changed about every 3,000
miles. This notion has been ingrained into people's heads for decades, in part
as a marketing ploy by oil companies. The 3,000-mile interval made sense when
engines used single-grade nondetergent oils. But with the latest oils and car
designs, it's no longer necessary to change oil that often under normal
driving conditions.
"You can change your oil every 3,000 miles if you're really particular, but we
recommend changing it every 5,000 miles," commented Tom and Ray Magliozzi, the
erudite grease-monkey hosts of the popular National Public Radio program "Car
Talk<http://www.cartalk.com/>," on a show last year. "If you change it more
often, you are just wasting your money and creating a disposal problem," they
noted. They are considering revising their recommendation to 7,500 miles.
Synthetic oils, because of their better properties, need to be changed less
often, at intervals up to 25,000 miles or more. In the end, the best advice on
the type of oil to use and the frequency of oil changes is to follow the
manufacturer's recommendation in your car owner's manual.
Chemical & Engineering News
ISSN 0009-2347
Copyright B) 2006 American Chemical Society
----- Original Message -----
From: William Beecher<mailto:wbeech@flash.net>
To: triumphs@autox.team.net<mailto:triumphs@autox.team.net> ;
'BMCU'<mailto:bmcu@autox.team.net>
Sent: Friday, May 11, 2007 3:29 PM
Subject: Re: [Bmcu] TR3 Oil
OK, I will admit to being a little out of the loop...it's been a while.
Just getting the '58 TR3A on the road, it has been sitting for 5 years with
fresh oil and I want to change it now that I have started and driven it
about 20-30 miles. The original manual calls for SAE-30 @ 40-70 degrees
and
SAE-40 @ 70+. Fifty years ago there were not all these multi-grade oils
available and I was wondering if a 10w-40w or some other combination is a
better choice these days.
I would appreciate to know what you all use for general use on the road and
around town, not competition.
Thanks,
BillB
TR3 (TS-303766)
"A bad day in your TR is better than a good day playing golf!"
Version: 7.5.467 / Virus Database: 269.6.8/797 - Release Date: 5/10/2007
5:10 PM
Version: 7.5.467 / Virus Database: 269.6.8/797 - Release Date: 5/10/2007
5:10 PM
_______________________________________________
Bmcu mailing list
Bmcu@autox.team.net<mailto:Bmcu@autox.team.net>
http://autox.team.net/mailman/listinfo/bmcu<http://autox.team.net/mailman/l
istinfo/bmcu>
[demime 1.01d removed an attachment of type image/jpeg which had a name of
8411oilimg1.jpg]
_______________________________________________
Bmcu mailing list
Bmcu@autox.team.net
http://autox.team.net/mailman/listinfo/bmcu
|