Date: Fri, 12 Sep 2008 00:19:30 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Ideal oil filter by-pass pressure/oil filters
In-Reply-To: <BLU136-W21695F1287C47219F4570DB550@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"
Ed,
Some of this is really getting anal but here goes.
The oil filter bypass is there to prevent oil starvation and filter
element damage if the filter can not pass oil and the pressure
differential exceeds a certain limit.
A cold engine with high viscosity (thick oil) will build pressure very
quickly as the pump will be efficient, bearing clearances tight, and yes
the oil thick. There is a relief valve in the engine to control the
pressure. This has nothing to do with the filter.
As the oil galleys fill there will be a flow surge. The filter may
restrict the flow so the bypass is there is needed to protect the filter.
If the filter should become clogged (will never happen in a maintained
engine) the bypass will allow some oil to get through.
Different engines can call for different bypass pressures because they can
operate at different pressure or flow rates. Early VW inline engines with
non hydraulic lifters had normal pressures even when hot of 90 psi. A
bypass differential of 30 psi would still allow that pump to get oil to
the bearings if it was needed.
The Water boxer on the other hand has trouble making 40 psi and at idle
the pressure can be below 10 psi. So here a lower pressure bypass of 15
psi is more appropriate.
As for oil filters effecting the lifters, it is all speculation and horse
non sense. Once the engine is warm, no oil filter is going to keep the oil
galleys pressurized after the engine stops. As a test, consider how many
times you change the oil and filter start the engine with the oil system
empty from the pump pick tube all the way through the filter and galleys.
If a lifter does clack it will usually quiet down in a few seconds. On a
worn engine you can even hear the rod bearings until they get oil.
There are two things that really cause the vanagon lifter syndrome. Where
the engine stops, (valves being held open), and the ability of oil to
refill the lifter after the engine is started. Then there are two things
that will keep a lifter from filling. One of the ball checks not working
properly or air trapped inside having enough pressure to keep oil from
flowing in. Usually the checks get stuck due to manufacturing tolerances
and letting the engine warm up and then driving will free them and make
things work. Engines that get started for quick moves around the yard or
that sit for long periods tend to get lifter syndrome frequently. When
shutting down a warm engine normally, the engine will tend to stop at a
cylinder TDC on its own. Stopping a cold engine or shutting down while
dragging the clutch in gear will tend to stop the engine where 1 intake
and one exhaust is likely to be held far open. Next start up can be a
clacker. I can make my Vanagons clack on demand.
Hopefully this helps you figure things out.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Edward Duntz
Sent: Monday, September 08, 2008 6:08 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Ideal oil filter by-pass pressure/oil filters
I'm trying to educate myself a little more about oil pressure, especially
as it applies to oil filters and by-pass valves in oil filters.
First, a little background. We already know that there's always been a
debate about which oil filter is right for the Vanagon. If not which
brand, then which model within that brand. There's also a feeling that
people who have had noisy lifters have discovered the "wrong" oil filter
installed, switched to the "right" one, and had the noise go away. A good
number of people swear by the Mann W719/12 filter for the Vanagon, and the
W719/5 for most other water-cooled, non-diesel VW's. So far so good. Those
who will allow for other brands to be used will go for, say, a Fram
PH2870A for the non-Vanagons, but say that it is not right for the Vanagon
because of the wrong by-pass valve.
Here is where my questions come in and why. I know that the purpose of a
by-pass valve is to allow for oil to by-pass the filter when the filter is
blocked (with too much dirt, for example) or when the engine can't push
the oil through the filter media on start-up because the oil viscosity is
too thick. But here's where I'm not sure of something- when the oil is
cold at start-up, does that increase or decrease the oil pressure? On the
one hand, I imagine a pump trying to move a liquid that is too thick or
heavy to move. Wouldn't pressure build up because there is no movement?
(Maybe I'm confusing this with backpressure.) On the other hand, if the
pump isn't moving the liquid, maybe the pressure is lower because it's not
moving it. I tend to think that the latter is correct. So having a filter
with the ideal by-pass valve opening pressure will allow the oil to flow
around the filter on start-up, but close as soon as possible to allow oil
to be filtered. Accoring to the VW Water-Cooled Performance Handbook by
Greg Raven, what we're really talking about is pressure differential, not
absolute pressure. I'm not sure if that clears things up for me or not,
but what he says is that you want a filter with a high by-pressure setting
like 32. I'm not sure if that only applies to other water-cooled VW's, or
Vanagons, too.
So what pressure differential is best for a Vanagon to have in its filter,
and is this different than other water-cooled VWs and why?
OK, enough with the questions, here is what my research found out about
various filters and their by-pass valve opening pressures:
Original VW 070 115 561 Can't find info
Mann W719/12 1 bar (approx. 15 psi) Thsi is the filter listed for the
Vanaogn
Mann W719/5 2.5 bar (apporx. 37 psi) This is the one listed for other
water-cooled VW's
Fram PH2870A 22 psi
Fram PH3600 12 psi
Wix 51342 16 psi
Wix 51516 8-11 psi
Purolator L20252 25-35 psi
Purolator L20195 12-15 psi
I got these filter numbers by using manufacturer's cross-reference charts
andy by putting in the Vanagon and other water-cooled VWs into their
application charts. What I found was that if you used the cross-reference
from the Mann, they tended to list the filter with the lowerby-pass
pressure setting. If you put in Vanagon, or other water-cooled VW, they
listed the higher by-pass spec filter.
Now since I haven't been able to find the spec of the VW filter, I've made
the leap (is it correct or not?) that the Mann filter has the correct
by-pass pressure spec. If this is true, then the Wix 51342 has the closest
spec at 16 psi.
So does anyone know what the VW filter by-pass spec is? Why is is
different for Vanagons than other water-cooled VWs (I do know that others
have a by-pass built in to the filter mounting, but that shouldn't really
make a difference in the specs, should it?) and what by-pass spec is the
best combination of letting oil flow at start-up , while not by-passing
too soon while running warm?
If you've read this far, I thank you for your consideration, and also hope
that the filter specs I listed are helpful to you in case you were
considering the same dilemma in choosing filters.
I'm going to post this on the Samba, too. It's nice to see varied
responses.
Thanks,
Ed in CT
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