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Old 01-09-2006, 11:05 AM
Join Date: Mar 2005
Location: X5world
Posts: 54
Xoutpost has disabled reputation
Contributed by: withidl

I am an ex lubrication engineer with Texaco Lubricants Company (now
ChevronTexaco). I’ve shamelessly plagiarized myself from
my posts from X5world and other forums (updating where applicable) and offer the
following composite of my posts for those that might be interested.


The primary reason for automotive manufacturers to specify relative low
viscosity engine oils is for fuel economy, i.e. the thinner the oil
(lower the viscosity) the less internal fluid friction there is in the
engine and thus less fuel is wasted in overcoming that internal

Viscosity is defined as a fluids "resistance to flow". The higher the
viscosity the thicker the oil the more resistant it is to flow.

Most modern engine oils are multi-viscosity, i.e. 5W-30, 15W-50, 5W-50,
etc. This is because an internal combustion engine operates in EXTREME
temperature ranges. At start up on a winter day the oil may be at 0
degrees, but upon reaching operating temperature the oil may be at 225

Lubrication in the engine is primarily "hydrodynamic". Think of a water
skier in shallow water that once up on the ski's is kept off of the
rough bottom due to the water not being able to flow out from under the
ski's as fast as the skier is able to slide up on the water. A car's
wheels "hydroplaning" over wet pavement is another example.

If a straight 30 viscosity oil were to be in an engine at 0 degree
start-up the engine starter probably wouldn't be able to crank the
engine against the oil's viscosity, and if it were able to start the
engine there would be oil starvation and damage to the engine due to
the 30 viscosity oil not flowing through the engine at 0 degrees. On
the other hand if a straight 5 viscosity oil were to be used at
start-up it would be OK, but when the oil reached the 225 degree
operating temperature the "skier wouldn't be able to stay off the
bottom", i.e. the hydrodynamic lubrication would break down (leave the
bearings to readily) allowing engine bearing parts to make contact and
spot weld at a microscopic level doing severe damage.

All of that being said, oil is formulated with "viscosity index (VI)
improvers" to change single viscosity base oils into multi-viscosity
oil. A 5W-30 weight (viscosity) oil is actually read as a "5 viscosity
winter (W = winter) grade - 30 viscosity summer (S = summer and
although not written is implied) grade". It is the VI improvers which
allow a single weight oil to behave as a 5 viscosity oil at engine
start-up in cold temperatures, but then behave as a 30 viscosity oil at
the engine oil's 225 degree operating temperature.

Engine oils are chemically complicated, being formulated with about 15%
additives which includes the VI improvers, detergents, dispersants,
antioxidants, anti-rust, anti-foamants, anti-wear, etc. The reason for
changing oils on a timely basis is due to the fact that the additives
are eventually consumed as they do their jobs. The filter removes
silicone (dust) and other particulates but does not replenish the

ADDITIVES – About 15% of engine oil is additives (synthetics included). These additives are generally as follows:

DETERGENTS – Just like laundry soap, they keep the engine clean.

DISPERSANTS – These keep the particles that have been cleaned by the detergents suspended in the oil until it is changed.

OXIDATION INHIBITORS – They retard oxygen in the
crankcase from deteriorating the oil. Oxidation will thicken the oil
until it, in extremely high heat situations, literally sets up like tar
in the crankcase.

RUST INHIBITORS – They react with and neutralize the
acids of combustion like sulfur (from the fuel) dioxide which forms
sulfuric acid with the water vapor in the crankcase. Sulfuric acid
would eat on the engine internals if not neutralized.

ANTIWEAR AGENTS – These are typically zinc
dithiophosphates. They rapidly react with the metals in the engine to
form a thin molecular layer which is relatively softer than the metals.
At engine start up, or when shock loading causes moving metal parts to
break through the oil film this relative soft reactive layer “shears”
away (and is immediately reactively replaced) instead of metal to metal
contact occurring with it’s resultant “spot welding” (at a molecular
level) which would damage the engine.

FOAM INHIBITORS – If oils foam due to the EXTREME
turbulence within an engine’s crankcase the foam will act as an
insulator causing the oil, which is a primary engine coolant, to retain
the heat it has absorbed from the engine and rapidly damage itself and
the engine. These inhibitors lower the surface tension of the oil
allowing entrained air bubbles to be released.

POUR POINT DEPRESENTS – These block paraffin wax crystal growth at low temperatures thereby delaying an oils “gelling”.

VISCOSITY – Viscosity is the MOST IMPORTANT attribute of
any oil. Viscosity is an oils “RESISTANCE TO FLOW”. To lubricate oil
must keep engine parts from contacting one another. A water skier stays
on top of the water because at speed the water can’t escape from under
the ski fast enough to let the skier sink. The same thing is happening
within an engine, i.e. the moving parts along with the pressure the oil
pump puts up keeps the moving metal parts “skiing” on top of the oil.
This is known as hydrodynamic lubrication. The higher (thicker) an oils
viscosity the more “resistant it is to flow” away from the moving parts
it’s supporting.

VISCOSITY IMPROVERS - Additive molecules which cause an
oil to not thin out as readily with temperature increases as it would
normally. This is what gives oil its “multi weight” rating. A 15W-50
“multi weight” or viscosity oil has ambient temperature properties of a
relatively thin 15 (W = winter grade) viscosity oil for quick
circulation at cold engine start up, but only thins out as if it were a
50 (implied “S” = summer grade) viscosity oil when the engine reaches
its operating temperature of a nominal 225 degrees.

Heavier/thicker/more viscous oils will consume more fuel due to fluid
friction which is why auto manufacturers recommend 5W-30 oils, but I’ll
trade a little fuel for the greater engine protection a 15W-50 oil,
which I use in my 2001 X5, affords anytime. NOTE that up North during
the winter a 5W-40 or 5W-50 engine oil may be necessary for cold
weather start up.

SYNTHETIC OILS – Synthetic oils by definition are "oils
produced by synthesis rather than by extraction or refinement". This
does not mean that synthetic oils don't start from a basic barrel of
crude oil.....they do. It's just that rather than taking the
lubricating oil molecules as they naturally occur in the barrel of
crude and separating them from the lighter gases (propane), lighter
liquids (gasoline) and heavier liquids (asphalt) through "extraction"
by solvents or "refinement" by distillation/boiling them off, the
lubricating oils from the barrel of crude are chemically modified so as
to produce a lubricating oil with a homogeneous molecular structure.
Regular oils have a “witch’s brew” of lubricant molecules which also
include paraffin. This “witch’s brew” has a nasty tendency to
deteriorate by readily reacting with oxygen in the crankcase.
Additionally, the paraffin at low temperatures crystallizes and “gels”
the oil which reduces its “pour point”. Paraffin does the same to
diesel fuel #2 at low temperatures and that’s why diesel #1 (kerosene),
which has much less paraffin, is used up North in winter.

The advantages of synthetic oils are that they flow at relatively lower
temperatures (due to not containing paraffin which "gels") and are much
more resistant to oxidation degradation at very high temperatures
(oxidation causes oil to degrade, thicken and loose their lubricating
properties). Because of their chemical stability synthetic oils can
withstand longer durations in the crankcase, hence the extended drain
intervals that BMW and other manufacturers recommend. The more
intensive refining is also much more expensive which the shelf price

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FILTER – The filter should be able to go the approximate
15,000 miles BMW’s service interval lights indicate. I personally drain
my filter (of most of the used oil) at an approximate 6,500 miles when
I change my oil and replace it at 13,000 miles. If the filter should
for some reason become clogged it has a bypass valve which will still
allow the oil to circulate to all engine parts.

Regarding how often you should change the engine oil, well it just
DEPENDS. If you’re only going to drive the vehicle 100,000 miles before
you trade it then you’ll probably never realize the benefits of more
frequent oil changes; hand that problem off to the next guy.

On the other hand, if you’re like me and plan on driving the vehicle
200,000+ miles then you’ll want to be diligent in this matter. Oil and
additives deteriorate over time (even if the vehicle isn’t being driven
much, hence the “annual” change requirement) due to engine heat,
oxidation, and reaction with contaminates and engine metals which
necessitates filtering and re-inhibiting or changing the oils. Because
of the relatively small amount of oil in an automotive crankcase
changing it and the filter is much less expensive than re-inhibiting
it. If you can do it yourself as I do it really isn’t expensive.

The “break even” point of engine wear vs. $$ again “depends” upon the
conditions the engine endures. It’s kind of like describing that
“normal” person ......... who just isn’t like any of us. So if your
going to keep the vehicle a long time be diligent, but if not, and your
conscience will allow you to trade it off to some poor unsuspecting
soul, then save the money.

Additionally, engine oils function to remove / distribute engine heat.
An aluminum piston melts at around 1,100 degrees F and combustion
temperatures above it are around 2,000 degrees F. If oil wasn't
constantly sprayed on the under side of the pistons they would melt.
Oil also carries the engine wear components which if analyzed on a
regular basis will predict maintenance needs prior to a catastrophic

In an engine the only down side to a high viscosity multi-grade engine
oil is fuel consumption due to internal fluid friction. It is for this
reason that BMW and ALL other vehicle manufacturers recommend 5W-30
engine oils as lower viscosity oils allow them to post higher mile per
gallon ratings.

High viscosity multi-grade oils are not a detriment to high revving
performance engines either, otherwise BMW would not sell 10W-60
performance oil for their "M" cars. These vehicles rev to 7 grand and
are subjected to much "shock loading" (like dumping the clutch), the
protection from which comes only in the form of a high viscosity oil,
thus the 60 viscosity to maintain hydrodynamic lubrication. Needless to
say fuel consumption is not the highest priority for the "M" cars.

In high temperature climates (I live in Houston, Texas) high viscosity
multi-grade engine oil is a MUST if one is concerned with engine

Again, I don't hesitate to swap a little fuel consumption for engine
longevity. I have a 2001 X5 4.4i with Dinan engine / transmission
software with 62K miles on it. For 22K of those miles I have towed an
8,300 pound GVWR 31 foot Airstream travel trailer with a 900 pound
tongue weight (X5 factory rating is 6,000 pounds GVWR and 600 pound
tongue weight, go figure). The X5 pulls this load in 5th gear 95% of
the time at speeds between an indicated 60 & 70 MPH and RPM varying
between 2,000 & 2,400. This high engine loading requires a high
viscosity oil and I have used 5W-50 and 15W-50 since the X5 was new. I
broke the engine in at relatively light loads and varying engine RPM up
to red-line before I ever heavily loaded it. The engine consumes an
approximate 1 pint of oil every 6,500 miles at which time I change the
oil (since the engine's oil capacity is 8.5 quarts this would equate to
a 5 quart engine's oil being changed at around 3,500 miles). I have
never had to add make-up oil between changes.


The API (American Petroleum Institute) forces "performance" conformance
through its service classification rating system which you'll find on
each quart of oil.

Looking at a quart of Castrol 5W-50 synthetic and a quart of Mobil 1
15W-50 synthetic, they both have "API Service S?/C?" (NOTE: I’ve used a
“?” to indicate the succession of alpha characters used in this
position) written in the "Circle" on the bottles. What this means is
that although they may formulate their oils using different additives,
both oils meet or exceed the API classification and are totally
miscible, i.e. you can add one to the other without damaging you engine
if you need make-up oil while traveling in an area where your engine
oil is not available. If by chance you cannot find synthetic oil you
can use a regular oil of the same API classification; additive wise
your OK, but you have “dumbed down” your synthetic’s durability and
pour point and should change it out at the first opportunity.

Incidentally, the S? stands for: "S" = Service (which = service
stations, garages etc.) = gasoline engine service and "?" represents
the current latest alpha classification that the oil manufacturers MUST
meet (started way back in the 1960s as SA, then SB, etc.)

Likewise, the C? stands for: "C" = Commercial (which = fleets,
contractors, farmers etc.) = diesel engine service and "?" represents
the current latest alpha classification that the oil manufacturers MUST
meet (started way back in the 1960s as CA, then CB, etc.).


All piston engines by design MUST burn some oil because their cylinder
walls are wiped with a film of oil by the piston rings during the
compression stroke and then this oil film is combusted along with the
fuel/air charge during the power stroke.

The break-in process is critical to the rings and their cylinder walls
so that they wear-in or "match sand" themselves AND their cylinder
walls to one other. This means initially keeping the engine rpm to a
relatively low level so that the metal asperities of the rings that
contact the asperities of the cylinder walls, generating immense heat
at a microscopic level, have enough oil cooling them to carry off the
friction heat without "spot" welding themselves together and tearing
out a microscopic piece of each other. If this "spot" welding does
occur it leaves microscopic pits in the cylinder walls which pool
additional oil which is then exposed to the combustion process and
burned off.

Additionally, if the “match sanding” is incomplete because the engine
rpm was never high enough to complete the wear-in, then the rings and
cylinder walls may never “match sand” to one another, leaving gaps
which don’t allow the rings to adequately wipe excess oil from the
cylinder walls during the intake and power strokes thus leaving the
excess oil on the cylinder walls to be combusted during the power

SO, the break-in should initially be at relative low rpm to ensure
adequate oil cooling of the rings and cylinder walls followed several
hundred miles later with some relatively high but short duration rpm
excursions to facilitate the “match sanding” process. After 500 miles
or so the duration of the higher rpm excursions can be increased until
the wear-in process is complete.

My own 2001 X5 4.4i which has 62K miles on it was broken-in accordingly
and I have pulled an 8,300 pound GVWR Airstream trailer for over 22K
miles with it (engine rpm between 2,000 and 2,700 with acceleration
excursions to 5,500). I use Mobil 1 15W-50 and I’m currently due for an
oil change since I have about 6,500 miles since the last one, but the
dip stick still shows the crankcase to be at the full mark.

Incidentally, above I was discussing only the cylinder rings and walls
but all of the moving parts of the engine and drive train go through
the same process of “match sanding” themselves to one another during
the break-in period so it’s critical to an engine’s longevity that it
be done properly. I suspect that the majority of those with oil
consumption problems did not break-in their engines adequately.

That being said, for an engine to burn a quart of oil every 2,000 to
3,000 miles would not be out of tolerance. All engines should consume
oil since some of the oil that lubricates the piston rings remains on
the cylinder walls and is combusted as the piston moves down on the
power stroke. A quart every 500 to 1,000 miles would be reason for

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Vehicles that are primarily driven relatively short distances, i.e.
trips that are less than 20 minutes duration, and if more than 20
minutes there are stops where the motor is shut off and allowed to cool
down somewhat, especially in a cold climate, are being subjected to
SEVERE SEVERCE. What happens is that due to the short duration of the
trips the oil is never coming up to full operating temperature of 225
degrees F for an EXTENDED DURATION. The primary product of the
combustion of gasoline is water, which on a cold day you see exiting
the exhaust as steam. Some of this water is "blown by" the piston rings
and ends up in the crankcase where it is absorbed by the oil via a
chemical additive known as an EMULISIFIER.

To give you something to relate to, Pine-sol Cleaner is an oil based
cleanser which you mix with water prior to use. If you remember, when
it is mixed with water it turns WHITE in color. What has happened is
that the additive EMULSIFIER in the Pine-sol has caused the water to
form microscopic spheres which are held in suspension and make the
mixture appear white just as snow appears white due to entrained air
within its crystals.

Essentially the same thing is happening in the engine oil. Its
EMULSIFIER causes the combustion water “blown by” the piston rings to
be held in suspension in the oil as microscopic spheres. This is good
because it keeps the water from settling to the bottom of the crankcase
or other low areas in the engine where it readily would promote
corrosion and possibly compromise lubrication.

The engine oil EMULSIFIER will release the water only if the engine is
brought up to full operating temperature and SUSTAINED there long
enough to allow it to boil off. The EMULSIFER, having released the
water, is then able to tie up more water the next time the cold engine
is started.

If the trips are of short duration and the engine oil EMULSIFER is
never allowed to release the water it has tied up by boiling it off the
EMULSIFER will eventually chemically separate from the engine oil as a
whitish substance (called “goop” by one poster), and the engine oil
will have been severely compromised and MUST BE CHANGED IMMEDIATELY.

Again, a vehicle which is driven on many trips of short duration which
don’t allow the engine oil to rise to full operating temperature is
enduring SEVERE SEVERCE. In this situation you should change the oil at
least every 6 months during the summer and every 3 months in extremely
cold winter conditions (an alternative would be to deliberately drive
the vehicle once every week or so for at least 30 minutes at highway
speeds to allow the EMULSIFER to release the water it has tied up).

The BMW X5 manual does not address this situation, and the service
interval calculator is obviously not programmed to deal with it.

Idling the engine at start-up only exacerbates the condensation problem
because during the entire time the engine is idling the combustion
blow-by (primarily water) is being absorbed by the oil emulsifier which
has escalated somewhat in temperature but not nearly enough to boil off
the water. Then during the first part of a short trip the oil MAY
become hot enough to start releasing the water but arrival at the
destination and shutting the engine down stops the process.

DON’T IDLE!!! Start the engine, let it idle for 30 seconds, and then at
first SLOWLY drive away until the engine comes up to operating
temperature before normal accelerations and speeds are used. The loaded
engine will heat up the oil much faster, putting much less water in the
oil so that less time will be required to release it once the oil is at
operating temperature. Still, a drive of less than 30 minutes duration
will not allow the oil to release all of the water its emulsifier has
tied up. If damage has already been done by too much idling and too
many short trips causing the emulsifier to separate from the oil, it
cannot be reversed, and again the oil MUST BE CHANGED IMMEDIATELY.

Additionally, if previously separated additive “goop” is not removed
from the engine when the oil is drained (and it probably cannot be),
the new oil charge is immediately compromised due to its emulsifier
being used up trying to absorb the water in the “goop” left behind.
Several back to back oil changes (at 500 to 1,000 miles) may be
required to normalize the situation. There simply should NEVER be any
"goop" or corrosion evident in a properly maintained engine!!

As to “why would BMWNA and their service managers say that there is not
a problem???” Well, they are actually correct in that the engine
doesn’t have an engineering problem. BUT where they fail the Customer
is in not advising the Customer that their vehicle is being subjected
to SEVERE service and does have a maintenance problem which will
require more frequent oil changes. But I’m giving them the benefit of a
doubt as I really don’t actually believe they understand the problem,
and what they don’t technically understand or have just come to accept,
they don’t want to admit to least they might have to deal with it. They
take the arrogant attitude that the Customer is ignorant (stupid??) and
will just accept what they say regardless of how ignorant (stupid??)
their (BMWNA & S/M) position may be.

For what its worth, to the other extreme, driving through a sand storm
at 120 mph in 110 degree ambient temperatures would also be considered
SEVERE SERVICE (and a severe attempt at suicide). The best service a
vehicle will experience is interstate mileage at a constant throttle
setting on a 72 degree day with only the driver on board.

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