New Diesel Engines and Oils Require Better
Filters
Recent design changes in diesel engines include moving the rings closer to piston
tops (as VW did in their A3 and A4 TDI engines compared to earlier Audi designs!
). to lessen the quench volume or dead space in each cylinder. The
burn is more complete, but soot still
forms. Because of the high rings, more of the soot gets
into the crankcase.
Oils are different. we have lower solids content, to
reduce the ash formed during the burn. Lower ash
means lower alkalinity, measured as total base number
(TBN), the percentage of alkaline material in the oil.
That means less detergent. New oils have to hold
more soot in suspension, but with a lower detergent
content, the soot will not be as well disposed. Alkaline
additives also neutralize acids and without makeup oil,
more frequent oil changes could be needed.
New fuels will help. They will have less acid producing
sulfur and lower aromatic content. Cetane levels will be
improved for a faster, more complete burn. White
smoke on start-up will be reduced and warm-up time
will be shorter. This will reduce, but not eliminate, acid
formation and soot.
Soot Damages Engines
Soot is an abrasive form of carbon. Oil carries it into
critical engine parts. Bearings, cams, lifters, rings, and
gear trains all experience premature wear unless
soot is removed from the oil. But ordinary filtration won't
work on micron sized particles.
The best way to protect your engine from the
effects of soot is through ultra-fine filtration.
Ordinary filter media cannot remove particles that
do the most damage. Picture a filter as a screen.
Openings in the screen determine the sizes of
particles that can pass through. As larger particles
are caught the screen openings are blocked and
they become smaller, Filtering efficiency increases
as smaller openings catch finer particles, but flow is
reduced as the screen gets blocked. Eventually the
screen clogs, cutting flow entirely. A loss of all
lubrication would cause the engine to seize.
Full flow filters are required protection on all
engines. The filter is located after the oil pump,
before the oil galleries into the engine. All full flow
filters have pressure relief valves. During a cold
start, when there is high restriction, the pressure
valve opens to let unfiltered oil flow. The
manufacturer's theory is that a small amount of dirty
oil is better than no oil at all, especially during a cold
start.
Full Flow Filters Can't Remove Particles
Causing Most Engine Wear
The newest full flow oil filters capture particles
down to 20 microns (a micron is 1/1000 of a
millimeter, or 0.000039"), but even finer soot
particles do most of the damage. Sharp, abrasive
carbon soot, dirt, and other impurities as fine as one
tenth of a micron can wear away metal parts in a hurry.
Particles in the one to ten micron range do most of
the damage. They are carried by the oil between all
bearing surfaces and rubbing components.
Full flow filters use special filter paper, pleated to
get more area in the cartridge. The paper is only a
few thousandths of an inch thick. Early unit-
removed 30 to 35 micron grits. Modern ones still
let through almost all die grits smaller than 10
microns. They get into clearances between bearings
and journals, cam lobes and lifters, rings and liners,
and into meshing gear teeth. To prevent abrasive
wear in these super critical areas, a better type of
filtration is needed; one that can remove these ultra
fine soot particles.
Bypass Filters Can Remove Smaller
Particles
There are two major differences between full flow
and bypass filters. First, full flow filters route all the
oil through the filter, while bypass filters send only a
small fraction of the oil picked-up by the oil pump
to the filter. The clean oil goes back into the
crankcase, effectively bypassing the engine. That is
why the filters are called "Bypass-type".
Although just a small portion is filtered on each
pass, within 30 minutes of engine operation, virtually
all the oil in a crankcase will be filtered. After an oil
change, clean oil doesn't have a chance to get
saturated with dirt and soot.
Second, bypass filters don't restrict oil flow in the
engine. They just clean better. Bypass filters can be
larger and finer than full flow ones. Modern bypass
filters force oil through
seven inches or more of tortuous travel in the filter
media. Most commercially available bypass filters
can trap particles as small as ten microns.
Engine makers recognize the benefits of bypass
filtration. Used in addition to, and not instead of a full
flow filter, it will not alter or void any engine
warranty. Bypass filters will be needed. Soot in
1998 engines is expected to be so bad that new filter
cartridges, combining full flow and bypass
technologies, have already been developed. These
are better than full flow filters, but they are
compromises. With both types of filters in one
housing, the volume of each is limited. The full flow
filter must be smaller, to make room for the bypass.
Bypass filter size is small compared to stand alone
units, so filter life is shorter. Combination filters arc
designed to be replaced between 8,000 and 12,000
miles, compared with separate bypass filters that can
last 25,000 miles or more.
Bypass Filters Are Needed to Remove
Engine Damaging Soot That Full Flow
Filters Cannot Trap.
The filter medium will make a vast difference in
bypass filter performance. Almost any form of
cellulose fiber will filter engine oil, but efficiency and
life are affected by the medium used, and how it is
made. Early bypass filters used sawdust felt, cotton
waste and even tightly packed wood chips.
Surprisingly, most performed better than full flow
filters, but they still didn't remove particles in the
critical zero to ten micron range. In a paper
delivered to the SAE (Society of Automotive
Engineers) in 1998, Needle man and Madhavan
made a Review of Lubricant Contamination and
Diesel Engine Wear (SAE 981827). They found that
full flow filters leave over 10,000 particles per cubic
centimeter that are five microns or larger. Of these,
ninety percent are in the five to ten micron range that
do the most damage. A diesel engine with 10 gallons
of oil can hold over 400,000,000 million potentially
damaging particles. Grits that pass through full flow
filters cause seven times more wear than those larger
than 20 microns can.