VANAGON archives -- September 2008, week 2 (#75)

Date: Mon, 8 Sep 2008 18:07:58 -0400 Reply-To: Edward Duntz <eduntz@HOTMAIL.COM> Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com> From: Edward Duntz <eduntz@HOTMAIL.COM> Subject: Ideal oil filter by-pass pressure/oil filters Content-Type: text/plain; charset="iso-8859-1"

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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