Date: Sun, 4 Dec 2011 10:43:04 -0500
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Oil recommendations simplified
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The attached chart is what VW offered for most of their models back in the
day. There are two considerations though. As a left over from the air cooled
days outside temperature did have an effect on the running oil temperature.
In fact overall engine temperature was effected by outside temp. I once
drove my 72 bus 400 miles and the oil temp never got over 120F. With the
water cooled engines except in extreme conditions the oil is going to at
least get as hot as the coolant and then some more depending on speed and
load. The other consideration is that the multi-range oils of the day did
not maintain viscosity well and often were not even stable. The science then
was nowhere as good as it is now.
There are two major requirements for oil viscosity. The most critical to
select is at start up. At the lowest temperature expected not only does the
oil have to allow the pistons to move at allow the engine to start, it has
to flow, be able to splash, and the pressure relief valve has to handle the
excess flow. As such the low temp ranges indicated on this chart are still
good. You do not want straight 40 oil at low temps due to start up concerns.
Things that happen with too heavy an oil at start up include cylinder
scuffing and wear, excessive oil pressure resulting blown oil coolers and
seals, locked-up spun bearings in the case and I have even seen the oil pump
drive tab sheared off. When we get extremely cold weather here on Long
Island I see many cars loose the crank and cam seals form them actually
getting pushed out from excessive oil pressure since the drains just can't
take it when folks start it up and drive without letting some warm up. On
the other end of the spectrum the oil has to maintain some minimum viscosity
at the highest bulk temperature to maintain film thickness for the bearings,
avoid washing past the rings, and maintain sufficient pressure. Here is
where the VW boxer engine, (both air and water cooled), need some attention.
These engines are really loose tolerance, that gets even worse as the case
expands and bearing clearances increase. To make matters worse the pump is a
simple design that also gets affected by expansion and there is very little
reserve. Then we need to run them close to 4,000 rpm and load them
continuously really driving oil temps up. Overfill the crankcase and some
other factors and it is possible to see oil temps of 250F or even more.
Thankfully we now have multi-weight oils that actually work.
SAE oil viscosity for straight weight oils is specified at 212F. For the
multi-weights the lower number is @104F and the upper is still at @212F.
This gives little indication of what the oil may actually be at extremes
like -10F or 300F. If we look at the product specs for these oils you will
see that @212F (where our oil should be),a straight 40 will be thinner than
at 15w-15 or 20w-50. So for us this is the better choice at both start up
and running for most temperatures. Now note the 15w-40 or 15W-50 is good
down to almost 0F. Synthetics with these same ratings can go down even
lower as they have very low pour points. So for most of us the 15w-50 is the
ideal oil for most conditions. Do note that in extremely cold weather after
start let it run for just a minute or so to get some heat in the oil and
drive gently and avoid revving the engine more than needed until you see the
temp gauge start to move or you feel some heat.
Most engines do not need the high viscosity oils. For the in line VW engines
the 5W-40 or 0W-40 oil works just fine. Most modern vehicles now even use
5w-20 or even 0W-20 oils. The vanagon won't like that stuff for long.
As for how often to change oil there are a lot of variables. The only way to
know is to do oil analysis. This is best done at the expected half-life of
your oil change interval. So VW recommended changing at 7,500 mile intervals
for both regular and synthetic? So at ~3,000 miles take a sample and send it
in. Be sure to keep the sample clean. The good test programs have pumps and
tubes and stuff to help you get a clean sample. Taking one out of the drain
pan is not good. The test results will tell if the oil needs to be changed
and why. Is it contaminated with dirt, fuel, coolant? Are there excessive
wear particles? Are they ferrous or tin/lead/copper, etc.? Is the oil itself
actually breaking down? Loss-Gain of viscosity or nitration? You may need to
do some interpretation and the lab will help if needed. Yes there is a cost
to this but I have saved many engines over the years due to detecting things
going wrong before the failure. Coolant and silica are the biggies.
As for synthetics being worth the extra money there is no doubt that
conventional oils are getting better and do a really good job. The
synthetics though are a premium product and even if the only benefit was
using them for longer periods the cost is offset. For our engines the
increased temperature range is a real benefit.
Dennis
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