RE: [A/S] Oil Change Suggestions? Trusting the manual?

["Oliver Filippi" <ofilippi@xxxxxxxxxxxx>]

There are a couple of caveats which, I believe, should be considered before
blindly following the car manual.

First, the recommendations in the manual are a compromise between what the
engineers who designed your vehicle and the marketing folks in the sales and
PR departments think.

Thus they do not necessarily reflect the best judgment in terms of vehicle
longevity or vehicle safety or performance.

Case in point:  Many years ago, the automakers recommended 24 PSI of air
pressure in the tires.  This was chosen to provide "a soft, comfortable
ride" rather than to maximize tire life or road handling capability. [More
recently, look what happened when the marketing folks recommended a low tire
pressure to "improve the ride" of the Ford Explorer. High heat build up and
tire failure on freeway driving, especially in the hot climates was a major
cause of tire failure with some very sad consequences.]

Today, there are different pressures (not tire, sorry about the pun) on the
automakers which are showing up in the "manual's recommendations."

Automakers are trying to convince their customers that their new vehicles
require less service.  The result is stretching the time between scheduled
maintenance.  Thus some service intervals are extended while others are
shortened. This also provides a means to support their dealers by including
maintenance which is (perhaps) best done by a dealer rather than an
independent garage - typically service which requires special test equipment
which may be unique or more available at the dealer.

Over extending lubricant lifespan is a common occurrence (but you will also
see the "escape clause" in the fine print, "if operating under severe
conditions the interval should be less." Or something like that.

General Motors has developed a computer model for its vehicles which is
quite good at predicting when the engine oil should be changed (assuming you
are using the oil recommended in the owner's manual).  It DOESN'T TEST the
oil, but calculates its life based on TRACKING THE OPERATION of the VEHICLE,
namely the distance (or time) traveled for each trip, the number of trips,
the engine temperatures achieved on those trips, the speed the engine is
run, etc.  Thus it can weigh stop and go short trips (around town) along
with longer highway operation (trip) and factor in the load put on the
engine from engine rpm and operating temperature {towing or hill climbing
loads).  Eventually, the computer calculation causes the "Change Engine Oil
light to come on. Note that a better performing lubricant (and filter) will
provide better protection and mechanical life than an inferior one.

Having said all that, one must recognize that lubricants (especially mineral
oils) have improved significantly in the past 40 years, both the primary
ingredients and the additives. On the other hand, today's engines operate
under more severe conditions - higher RPMs, higher temperatures, etc.
Likewise, automotive parts are machined to much closer tolerances, which put
different stresses on the lubricants, than in the old days. Thus, if a
vehicle comes from the manufacturer filled with a synthetic oil, you would
be well advised to continue using the synthetic.  This suggests that the
manufacturing tolerances are compatible with the synthetic right out of the
factory. If it doesn't come with synthetic, I would go a few oil changes
with the mineral oil (to allow the engine to "break in") before switching to
a synthetic.  There is no question that a good synthetic of the proper
viscosity and formulation for the intended use (gasoline or diesel, turbo
charged, etc.) is a superior lubricant (vs. a mineral based oil) which will
extend the useful life of the engine. So if you intend to keep the vehicle
for say 100,000 miles don't sweat the extra cost of the synthetic - consider
it an investment in your vehicle.

Clearances between parts in a modern engine are far more controlled and
consistent (where necessary) than ever before.  Thus automakers can increase
the clearances between mating parts to reduce friction, OR they can tighten
them up a little (but not too tight) so the engine (or transmission, etc.)
can use a lighter weight (thinner) lubricant, which, in turn, reduces
internal friction and improves fuel economy without it leaking out or
burning up.  Right now, fuel economy is such a big item that the automakers
will do almost anything to improve it. Likewise, modern lighter weight oils
(usually the ones spelled out and recommended in the manual) are labeled,
"Energy Conserving" which means that they usually are formulated with
"friction modifiers" - chemical additives which make them "slipperier", as
well as additives to hold the viscosity stable over a wider temperature
range.

Note that good synthetic oils are naturally (because of their chemical
makeup) more consistent in viscosity over a wide temperature range [do not
get as thick when they are cold, and don't thin out very much at high
temperatures.)  Also, they are less prone to heat breakdown (deterioration
under high heat operation (like towing up a hill), tend to be more slippery,
and generate less internal friction, as well as have a stronger film
strength.  This latter attribute means that a thinner oil (with less
friction or drag) will still lubricate adequately and still not allow metal
to metal contact (which causes wear) and offers improved fuel economy. Is it
any surprise that good synthetic lubricants are often superior to mineral
oil based ones?  Many of the lubricants installed in a new vehicle these
days are synthetics for the above reasons, and the mechanical components are
specially designed to function ONLY with these special lubricants.  Examples
include limited slip differentials, 4 WD transfer cases, etc. - with more
coming.

Engine oil must also deal with the contamination issue, which can terminate
its useful life before the base lubricant is "worn out".

Many posts have alluded to the notion of testing the oil to determine if it
is due for a change.  Here economics enters into the picture (which has not
been addressed in posts thus far).  Very heavy duty vehicles typically have
large oil capacities, so a lot of oil (and expense) is involved in replacing
the lubricant. Thus the cost of testing the oil is easily justified.  As the
cost of the oil change drops, the expensive of the oil test becomes less
cost effective, so a less technical, but conservative guideline may be a
better choice.

Regardless what the manual says, I use a more pragmatic approach, which is
as follows:  Change the oil per the manual, but note how much quieter or
faster or smoother the engine runs on the fresh oil (immediately after the
oil change).  Chances are, there will be a very significant difference.
That shows that the lubricant that was replaced was well past its prime and
causing more friction (and wear) than the fresh lube. Next time, change the
oil a thousand miles sooner, and note the difference. Eventually, you will
determine how long the oil can go before its function is compromised.


Oil Change for Dummies: (If the forgoing is too much to digest.)

As a rule of thumb, today's vehicles under normal operation can typically go
2,500 to 3,500  miles on a mineral oil and 4,000 to 6,000 miles on a
synthetic without pushing things. Gasoline engines typically can push the
upper limit, while diesels will be nearer the lower limit.

Good luck,

Oliver Filippi

P.S. And don't forget - "Oil is cheaper than metal!"