Some Slippery Information
by Terry CIeland, UCR Member
Oil is the blood of an engine and just
like the blood in our own bodies it does many things. Oil just doesn't
lubricate, it carries away heat, it dissolves contaminants, it carries
away debris and provides a working medium for such things as hydraulic
lifters.
All oils, whether mineral stock or
synthetic have additives mixed into the package. This package is a
melange of chemicals that allow the oil to do its other jobs. It seems
to be a popular belief that if high priced synthetic oil is used in an
engine that oil changes can be further apart and you will realize a
huge increase in power or efficiency ...well, NOT QUITE! No matter
what the main constituent of the oil is (mineral or synthetic)
approximately 60% of the container's content are additives.
Interestingly the lifetime of the additives (the time it takes to lose
its useful properties) varies but it is primarily dependent on the
service duty of the engine and to some extent in which kind of oil
base stock it is mixed with. It is in fact the "death" of
these additives that dictates when your oil should be changed. Not all
oils are created equal but all of them "wear out"
approximately at the same time as the additive package is depleted.
The bottom line is that frequent oil changes are better for an engine
(within reason) no matter what the marketing propaganda says. If you
feel better spending BIG $$ on the more expensive oil, then GREAT (for
the marketing guy!).
Just one word of caution here. Always
remember that you get what you pay for, so if you drive a quality
product or really care about long engine life, then spend at least
enough to get a good quality motor oil with a good name brand to
support it, never use the bargain stuff. Remember a cardinal truth;
OIL IS CHEAPER THAN STEEL
SYNTHETIC vs. MINERAL
(battle of the advertisers)
The differences between these types of
oils are all in the molecular makeup. Synthetic oil has a very
consistent molecule size which gives the oil very good and consistent
properties. Mineral oil being a product of nature has lots of
different sized molecules in its makeup. The advantage of synthetic is
that it potentially has a more stable suite of properties that can be
tailored to a wider range of applications. This is why you can now
find oils that can cover huge viscosity ranges such as 15W40 and even
OW30! There are definite advantages to this ability but careful
consideration of application is necessary.
To review some of the oil jargon let's
look at what the numbers and letters mean that I just referred to.
Viscosity is determined by measuring the flow properties at a fixed
temperature. A base number is set as standard then relative flow
numbers are assigned to describe the relative viscosity of the oil
being measured. The lower the number the "lighter" the oil
is. That means it flows much easier at the same temperature than one
with a higher viscosity rating. There are single viscosity oils so it
is simple to understand that 10 weight oil flows easier than a 30
weight oil under that same temperature circumstances. Multigrade oil
is what has become possible due to additive packages and has been
further enhanced by synthetic oils. A number such as 10 W 30 means
that the oil has variable properties between this range of
viscosities. The best thing about this is that it can compensate
(within its designed capability) for the negative effects of
temperature on viscosity. High temperatures drive viscosities down but
multigrade oils have the ability, due to their additives, to
compensate. So back to our 10 W 30 example. The 10 means that it has
the viscosity (flow properties) of a single grade 10 weight oil at LOW
temperatures. The "W" following the first number is the
convention that
verifies this tested ability. The last
number is the viscosity rating at HIGH temperatures. The working
temperature range is approximately between 0 and 100 degrees Celsius.
Things go out of whack above and below. Above 100 degrees C. the
viscosity begins to lower as it would with single grade oil. The
viscosity can be lowered by as much as 50% for higher than 100 deg. C
temperatures.
You need "thinner' oils like 10 or
multigrade with 5W or 10W when the engine temperature is low
particularly here in Canada where we can see quite cold temperatures
even in good driving months, never mind winter. This low viscosity
allows the engine to receive vital lubrication. Imagine trying to pump
grease versus olive oil. A 30, or worse, a 50 weight oil would look,
feel and work just like grease at 0 degrees Celsius. Your engine will
suffer. Olive oil would in fact work better under these conditions,
but not for long!
The need to have good lubricating
properties at low temperatures but then have good lubricating
properties at high temperatures is what has stimulated the development
of multi grade oils. So our 10 W 30 has the easy flowing viscosity of
a 10 weight oil when cold and then the lubricating properties of 30
weight oil when it is hot. Just what we need in a country like ours
where the temperatures are widely variable at nearly anytime of the
year.
Engine design has a lot to do with
which grade and which type of oil you should choose. If the engine was
designed to work with a single grade mineral oil with its multi sized
molecules and low or high single grade viscosities then using
something "better" may not have any significant benefits. If
however your engine is designed to exploit the benefits of multi grade
fully synthetic oil then that is exactly what you should be using.
Therefore putting new multi viscosity synthetic oil
in your old iron horse could present a
problem and vice versa.
Advertisers are not engine designers.
They publish brochures to make people think that they are getting
better value or in some case something for nothing. Go by the
manufacturers recommendations. They are the ones who have designed and
extensively tested the engine and know what it needs.
ADDITIVES
(snake oil)
It is always easy to design some tests
to show how some off the shelf additive will enhance the oil's ability
to do ONE thing well. The problem is that the oil has many jobs to do,
not just one. Some of these additives could actually hamper the oil's
ability to do the rest of the things it needs to do. The oil has to
carry away wear particles, control acids that form from combustive
residue, it needs to deal with the mixture of combustion by products
and condensation from varying temperature cycles, it has to allow heat
transfer, it has to deposit anti wear particles like Teflon on the
moving surfaces and many other such things such as dealing with hydro
carbon dilution from unburned fuel, and on and on. Most oil
manufacturers will tell you that their oil already has things in the
additive package to help oil do what the snake oil salesman says that
his special brand of elixir will do. The difference is that the oil
manufacturer has blended their product in the right proportion so that
the oil and its additive package can fulfill its entire job function.
Snake oil salesman are merely pitching the "more is better"
idea.
SEVERE SERVICE (Who
me?)
I spoke of severe service and how it
affects your oil change intervals and other matters but just how do
you determine the degree of service? >
Any operation of the engine beyond the
designed operating range breaks down the additive package more
quickly. When the additive package is done in, so is the oil. The more
frequently that you stress the additives the more quickly it will
deplete. Since the additive package is put there to help deal with
this less than perfect operating conditions you can assume that you
are making a withdrawal from the additive protection bank each time
you push the operating envelope. You will have to run to the bank with
a fresh oil deposit more often in such cases.
Is this the only definition of severe
service? No. Severe service just doesn't mean pushing on the gas pedal
harder and more often it also means the way in which the engine is
operated even within its normal operating range. Frequent starts and
stops, short temperature cycles such as quick trips to the store, low
total mileage with long periods between uses are just as hard on the
oil as the weekend track session, sometimes even harder! Heavy shoes
are not the only causes of severe service. In a situation where
someone is a more aggressive driver or even races their car the
contamination in the oil is totally different than the case of the
Sunday driver. The cool and slow drive is the worse for raising
hydrocarbon dilution levels which has a negative effect on oil
viscosity and therefore its lubrication properties. This means more
wear, less vapour burn off and it is tough on the additives.
So, each type of severity affects
different things in the additive package but the net result is the
same; the oil change frequency must be increased in order to replenish
the additives and to remove the waste material and wear particles held
in suspension. The latter reason is why you just can't top up the
additives with that snake oils salesman's potion or buy into that
longer oil change interval because you spent a fortune on fully
synthetic oil. You still need to get rid of the dirt, which is the #1
cause of engine bearing failures!
ANOTHER LOOK AT THE LABEL
(don't look for them at Tim Horton's)
There is a "doughnut' on the oil
bottle that bears your attention. Not only is the viscosity stated on
the round label that is commonly called the doughnut but also there
are symbols that you should understand. When the car manufacturers'
design the engine they choose from a variety of oil specifications,
more than just the viscosity. You will see symbols like SF , SG , SH
or CC , CD. BE CAREFUL! The oil that is prefixed with the letter
" S" designates it for Spark Ignition engines. The prefix
"C" designates the oil for Compression Ignition engines
(Diesel). The allimportant additives are very specific to dealing with
the byproducts of these very different fuels (gasoline vs. diesel).
The suffixes are important too whether
for gas or diesel engines. The suffix designates the specific standard
to which the oil has been tested and has met. Sometimes those standard
are set by the engine manufacturer themselves. Note also that recently
the labels have been changed. Only a short while ago most motor oils
were able to meet the specifications of both gas and diesel and you
would see this combination approval on the doughnut in the form of SG,
SH/CC, CD. Now they are most often separated but you cannot tell
unless you look at the doughnut. Now that you know how important the
additive package is to the whole motor oil requirement you will want
to be absolutely positive that you are getting the best protection
from your oil selection.
OIL IS CHEAPER THAN STEEL
Better believe it! Use the right type
of oil and change it more often than recommended. If you know you
qualify for severe service than change it more often still.