[Vwdiesel] Risks of straight weight

[Val Christian]

We have a local statistician, who for 30+ years has tracked engine maintenance
at several facilities.  He is a proponent of condition based maintenance,
and says that the costs of condition-based maintenance are less, and 
downtime is less than scheduled maintenance.  This primarily refers to 
aircraft engine overhauls, but is relevalent here as well.

In his data, which is limited, due to the more limited use of multivis 
in aircraft, (limited to about the last 20 years), he says that the 
data suggests that camshaft and camshaft bearing failures happen less
in straight weight applications.  The local tribologists (three) confirm
that this is likely the case, particularily in OHC engines (which most
aircraft are not).  The reason is that a multivis, with a lighter base 
oil, "drains down" faster.  [My opinion is that this is not much of a 
problem in a daily driver, and a greater problem in the tractor used
once or twice a week. -Val]  

I asked (the statistician) about main or crank bearing failures.  In his
database of thousands of engines, he had three cases of crankshaft and main
bearing failures.  All three were secondary to camshaft failures.  All 
three were Lycoming O-360-H2D, which had a "tendancy" to experience 
camshaft spalling, and subsequent contamination of the engine oil supply.
Two of the three had oil screens, and one was retrofitted with a single
element oil filter (11 micron).  He personally inspected all three failures,
and stated that the particulates were copious within the crankcase.  

In his data, there were no spun bearings due to lubrication failures of 
the oil.  There were 8 instances of oil pump failures, but none resulted
in a failed crankshaft.  The highest time engine in his data base is over 
14,000 hours, and the average is over 2500.  The engine types he has tracked
the most are aircraft, construction equipment, farm equipment, refrigeration
(small diesel), pumps, stationary generators, highway repair and maintenance,
and more regular vehicles when accurate record keeping was available.
[My diesel Rabbits, Volvo, Ford van, Rambler American, tractors, etc.
are in his database.  -Val]

I didn't write down the total count in his database, either in entries or
in engines.  I'll ask next time I talk with him.

The principle risk of straight weight oil in extreme weather is that
of the oil gelling and cavitating the oil pump.  In Alaska, many aircraft
operators will drain their oil overnight.  In less cold parts, propane
preheaters are commonly used.  I had personal experience in the early 80's 
with an aircraft with 100 weight oil (50 weight for cars), that had to
be moved in -10F weather.  The plane was preheated until you could warm 
your muffins on it, and then started.  Oil pressure came up right away, and
the plane was sucessfully flown to central Flordia.  Operationally, aircraft
with 100 weight oil are regularily flown in very cold conditions (at altitude),
without problems.  The risk exists at startup.

There is some risk mitigation with cold WX starts using striaght weight
oil, because the residual oil in bearings has better lube properties than
a corresponding quantity of multivis oil.  Additionally, there will be more
oil regionally present, due to less "drain down."  Monitoring engine 
oil pressure, and permitting temps to come up prior to applying load
and also to increasing engine RPMs, is another good risk mitigation
strategy.

Relative to VW diesels, in the late 70's and early 80's there were
cases of filter failures on Rabbit diesels.  I commonly used PER-1 or
LF-1 filters, because they were commonly available, and were slightly 
larger than the VW filters.  Available at any discount store, they 
were cheap (I still have scores in my basement, probably bought for 
$1 or so.)   In  the early days of VW diesels, 20W-50 oil was commonly 
used.  I certainly did.  Still have many cases of it.  Well, on -10F and
-20F mornings, some operators would start their cars, and pop onto the 
expressway.  The high oil pressures which resulted, caused filter canister
failures.  I never had it happen, but I know of several people who did,
and the dealer, at the time, said they had several cars in one day, with
filter failures.  Fram makes a heavier walled filter, which is commonly
available, and is slightly smaller in diameter.  Easier to fit on my Jetta.
But the Rabbits had easy access to the filter, and the larger filters fit 
fine.

In summary, there is a trade between the greater lube benefits and 
better additive selection (or rather de-selection) of straight weight
oils, and the cold-start temperature flexibility of multivis oils.
If cold-starting, with at times unpredictably cold temperatures, is 
a common event, then multivis oils may be for you.  If long life is
a concern, then straight weight may be in your interest.  The bottom line
is that there are many more causes of engine failure, and oil failure 
is not real common...even using the cheapest of storebrand oils.

My choice is to run straight weight oils from about April to November, 
and then use multivis oils.  In November, and April, when temps drop
below about 25F, I give the oil a chance to circulate prior to 
hitting the road, and punching the "rocket mode" my old diesels have.
Right.

Val


ps: Ask me why I don't run 20W-50 oil in my diesels anymore.  I used to 
run it year-round.



> 
> >The damage you can do to crankshaft bearings by forgetting >to change your straight grade oil when it gets cold far >outweighs the benefits that may be there in running the >straight grade oil in the long run.
> 
> Are crankshaft bearings the usual thing to get damaged at 
> low temperatures when running single grade oil of the 
> wrong grade?
> How easy is this to do?
> 
>    --  Gavrik
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