RE: [A/S] Oil Change Suggestions?

["Oliver Filippi" <ofilippi@xxxxxxxxxxxx>]

It seems to me that this discussion on oil and oil changes in diesel engines
is missing the main point and obfuscating the realities of the factors
involved.  I have owned several diesel (and turbo diesel) powered
automobiles and have put over 200,000 miles on each of them without engine
problems.  Any experienced diesel engine user will tell you that it is
essential to put good clean fuel in the engine and good oil in the
crankcase, and change it often.

First, there is Filippi's Law, namely, "Oil is cheaper than metal."  So
don't be penny wise and dollar foolish.

Having said that, changing the oil too often (though it cannot harm the
engine) is a waste of money.

Recognize that oil in an engine is due for a change when EITHER of two
factors takes place:

1. The oil is no longer capable of adequately lubricating the engine (from a
friction reducing standpoint).

Or

2. The oil contains a significantly high concentration of chemical
contaminants to damage the engine.

Both factors are clearly caused by overly long oil change intervals, but
other factors can have an influence as well.  Note that oil can physically
break down from heat, (or extended exposure to heat) and thereby lose much
of its lubricating qualities.  If this compromised oil is circulated through
the engine, it will cause excessive wear on the engine's lubricated(?)
parts. This is a particularly significant factor in turbocharged diesel
engines.  The turbocharger's turbine is mounted on the exhaust manifold (one
of the hottest parts of the engine) and oil is pumped through the
turbocharger's turbine bearings to lubricate the turbo.  This is essentially
pumping the oil through a FLASH OIL COOKER.  Hence any oil or additive which
cannot take the heat (or is susceptible to deterioration from heat) will
break down and do its job less effectively.  Thus, the engine oil you use
MUST BE FORMULATED FOR USE IN A TURBOCHARGED DIESEL ENGINE! Such oils are
capable of taking the heat.

Good synthetic oils typically tend to be less susceptical to heat breakdown,
so there is a POSSIBILITY for an extended oil change interval.

Physical contamination of the oil (synthetic or conventional) by worn metal
is a function of operating environment (short trips, engine tolerances,
etc.) If the oil has better lubricating qualities, obviously, there will be
less physical wear of the engine and less worn metal contamination.  Here,
synthetic oils have the edge (although conventional mineral oils can have
friction modifier additives to reduce friction {"energy conserving"
oils)(and with it, mechanical wear).

The downside of the good synthetic lubricants is that they are such good
lubricants (low friction) that the engine will not "break in" if they are
used from day one. Break in is less of an issue in recent years as most high
quality engines are machined to incredibly close tolerances and need little
break in. This allows them to use lower viscosity (thinner) oil for reduced
friction and better fuel economy.  The precision machining of today's modern
engines would have been considered impossible only a few years ago.
Industrial reciprocating (piston type) air compressors have been using
synthetic oils for many years with great success.  However, they are
typically run on conventional mineral oil for the first 100 hours or so to
"break in" before switching to synthetic, after which they run for an
extended life. [I doubt that air compressors are machined to the fine
tolerances of modern automotive and truck engines.] Note that the major
contaminant in air compressor oil is water (if the duty cycle is short and
the compressor does not operate at a normal operating temperature (which
will boil off the water).  Personally, I would go one or two oil changes
with a conventional mineral oil before switching to a synthetic - unless the
engine came from the factory with the synthetic.

A diesel engine's oil is contaminated by the blow by (gases which get past
the piston rings and into the crankcase) of products of combustion (in
addition to water - another byproduct of combustion).  Sulfur, for example,
when burned becomes sulfur dioxide (and/or sulfur trioxide) which when mixed
with water (or steam) becomes sulphurus or sulphuric acid, which can do a
job on internal engine parts.  To counteract this, diesel engine oils have
additives which can neutralize these acids, but have a finite life, (and
finite capacity to neutralize the acids) and hence are exhausted by the
contaminants if not changed often enough.  Note that diesel engines
typically have an 18 to 20 to one compression ratio (compared to 8 or 9 to
one in a typical modern gasoline engine).  This higher compression ratio
leads to more blow by and hence more combustion caused contaminants in the
engine oil which, if not controlled, can have a detrimental effect on the
life of the engine.  Oil filters can remove the physical contaminants
(metal, etc.) but not the chemical contaminants, nor undo the heat caused
oil degradation.  Thus the folly of just changing the oil filter and not the
oil (even if the oil doesn't break down form the heat).

The only practical way to get rid of the unwanted chemicals is to change the
oil, period.  Note that many heavy duty industrial diesels (and those in
long haul trucks) often have much higher oil capacities than light duty
diesels, and have large oil coolers (that big round cylinder on the outside
of the engine compartment) to reduce heat breakdown.  The larger oil
capacity dilutes the chemical contaminants (while increasing the amount of
additives - more oil) and allows the engine to go for a longer period (miles
or hours) before an oil change is needed. [This is why long haul truckers
often chemically test their oil before making the decision to change it.]
Typical light duty diesels (most Airstream tow vehicles) have neither large
oil capacities nor large oil coolers and will require more frequent oil
changes. Note that the amount of oil involved may actually be similar, say 5
quarts every 3000 miles vs.. 20 quarts every 12,000 miles.

Note that although synthetic oils may have a longer lubricating life, (less
friction [heat] break down) they are still susceptical to chemical
contamination (consistent with the capabilities of the additives in the
oil), and must be changed sufficiently often to remove these unwanted
contaminants.

Bottom line:
Use an oil (mineral or synthetic) of the proper viscosity formulated for use
in a turbocharged diesel engine. Read the label. If it says "approved for
Mack truck, Cummins, Navistar (International [Ford]), Caterpillar earth
movers,Detroit Diesel, etc." you are OK.  If not, don't use it. Most of the
major oil companies offer such oils, Chevron Delo 400, Mobil (I think)
Delvac, Shell Rotella T, etc.  They also offer synthetics, Mobil 1 (for
diesels - not the gasoline engine version, Shell Rotella T Synthetic, etc.
You may have to go to a truck stop or truck service facility to find them.
{I have purchased Shell Rotella T Synthetic and Chevron Delo 400 at Costco
and Wal-Mart.} There are also specialty synthetic oil manufacturers, Amsoil,
etc.  But here again, make sure the oil is approved by the heavy duty engine
manufacturer.  Beware of exaggerated claims of long oil life, or very long
oil change intervals.  The laws of physics are against it. And don't ever
forget, Oil is cheaper than metal.

Good luck, and enjoy your diesel.

Oliver Filippi