I have watched this thread for a while and opinions are being based on hearsay,
wife's tails and rumor. In the end your questions
can only be answered with investigation and the associated tests. I personally
do this from time to time. Once is not enough, as
the filter market continually evolves. So let me offer the results of my testing.
There is a huge difference from one filter to another. Those differences are
particulate size that the filter traps, the amount of
internal resistance of the filtration process in pressure drop across the filter
and lastly, particulate trapping capacity. In all
these cases, size matters. The larger the better. Please notice that I did not
mention a valve, because very few have them at all.
If they do, it is a band aid in engine design, as is the use of these small
filters. Filter size is primarily driven by available
space. Today, in almost all cases, the filter is of the full flow variety, as
opposed to the older bypass variety. The oil pump
will have an overpressure valve that will lift when the spring pressure behind
the bleed ball in exceeded. All full flow filter
installations also have a similar valve parallel to the filter. That valve will
allow oil to flow around the filter when the
differential pressure across the filter exceeds the design value ensuring
adequate oil flow when the filter is full of particulate
or the viscosity of the oil is too high. Please note there is no warning light
that your engine is no longer being protected by
the filter. Please be aware of the fact that automotive oil has additives that
keep any particulate in suspension in order to
allow the filter to remove them. Please consider in that light how important
pressure drop as a consideration it in filter choice.
Now the wife's tail, drainback is unavoidable. Every customer of the oil
galleries will drain the galleries in the absence of
resupply. 90% of all engine wear occurs during startup due to the lag from pump
start to delivery at the customer interface. Just
because you observe oil pressure doesn't mean there is full lubrication. This is
especially evident in cold weather when the
viscosity of the oil raises observed oil pressure, but with sometimes
drastically reduced flow. The next time you see an
industrial engine (100% duty cycle) look at the oil filter. You will very often
see as many as 4 huge units. There is a reason. A
pressure gauge or a light only tells two things, the pump is running and there
is resistance to flow. Everything else must be
assumed. Large expensive engines use electric pre-lube pumps to address this
issue. The larger the engine, the longer this lag is.
So as an average user, how do we use this new found knowledge.
1) Use the largest filter you can fit rated for, at the most, 20 micron.
2) Use the lowest possible viscosity oil allowed by the manufacturer regardless
of startup engine noise. Remember it's all about
flow, not pressure.
3) Never disable the thermostat, oil temperature 200 degree F or 90 C is
critical in vaporizing internal engine condensation.
Water will combine with residual sulfur creating Sulfuric Acid, which corrodes
the oil creating sludge.
4) Change the oil frequently. More so in the winter. High tech synthetics do NOT
reduce this requirement. This is especially true
with small filters, cold temperatures and short trips. Remember oil filters
filter. They do not recondition the oil. The additive
package is consumed over time and acid buildup is unavoidable.
5) Always allow the engine to run at least 2 minutes before applying load.