TheSamba.com :: View topic

Tue Aug 26, 2008 4:23 pm

I have two different Mann oil filters on my shelf and am ready to chage my oil in both my 1.9 and my 2.1 Vanagons. I know that they need the anti-drainback/check valve. I thought that was what I was seeing just under the rim of one of them- the W719/5. But one online source lists W719/12 as the correct one for all water-cooled Vanagons, and there's nothing visible inside like the 719/5. The 719/12 looks more like an ordinary Fram. So which one is the right one, and should I be able to see the check valve? What is that thing that I'm seeing in the 719/5?

Thanks,
Ed in CT

Wed Aug 27, 2008 6:26 am

OK, any ideas here? I've searched past posts on the subject but have had no luck. It seems Van-Cafe sells the W719/12, so I'll assume that's the right one, but I'm just wondering what I'm seeing in the 719/5 just under the threaded end. Is is a by-pass valve, and not the anti-drainback valve? Frank on the Vanagon mailing list described what the anti-drainback valve should look like, but that's not what I'm seeing on the 719/12.

Anyone?

Thanks,
Ed in CT

Wed Aug 27, 2008 7:30 am

Some more info from someone on another list has helped me a little, but has also prompted more questions.

I see the anti-drainback flap on the W719/12. But I also see something similar on a Fram and an STP that I have as well. I thought the idea behind using a Mann or Mahle was that they have the anti-drainback valve and the cheap ones don't. So what is it that I'm seeing on the Fram and STP?

Where's the oil filter expert here?

Thanks,
Ed

Wed Aug 27, 2008 12:00 pm

Ed, I'm no expert, and the plethora of products on the market can be overwhelming, but this is one of those many subjects where in the absence of accurate info, uninformed speculation fills the void. A few pics and explanations might clear things up a bit.

Here's the deal: nearly any spin-on oil filter sold today of any brand or size has both bypass and anti-drainback valves built in. It's just standard for the industry. There are exceptions, but they are generally for special applications. But as you'd expect, how these things are accomplished differs.

You've just done your own little survey, and found that out for yourself. If someone went thru every OF on the shelves at a FLAPS, you would find very few that don't have the anti-drainback valve (ADBV), which is easy to see thru the openings of the endplate.

And here's the funny part: people sweat about whether there's an ADBV, but the question is doubly moot; nearly every filter you can buy has one anyway, and it's only needed if your filter lives on its side or upside down, as they do on many engines. The way the Type4 and wbx hang their filters, the ADBV is superfluous. I've considered this at length, and don't see how oil settling can siphon out the contents of the filter. The physics of that just don't work. And every time I've removed a filter that is situated this way, it has been overflowing with oil no matter how long it has sat. But it doesn't matter, because if you buy a spin-on filter, chances are you're going to get an ADBV whether you need it or not.

I just went out and took some pics of a Mann I cut open awhile back, so everyone can see what the insides look like. The ADBV in a 719/12 looks like this:

You can see it's just a silicone, EPDM, or other soft rubber disc that acts as a low-restriction check valve right below the inlet openings of the filter:

But the Mann bypass valve can't be seen from just looking at the filter, because it lives in the bottom endcap of the element.

This is the Mann element taken out and inverted. Its bypass valve is built into the element cartridge. Here I'm depressing the bypass valve's little rubber disc against its counterspring:

Flow thru the element is from outside-in, up and out thru the center spigot. The pleated element is supported thru its center by a perforated metal sleeve so it won't collapse. When pressure is above the valve's opening pressure, it forces the little valve at the base of the element casing open and allows a portion of the flow to bypass the element. If it didn't, when the medium can't allow all the oil to flow thru, the element pleats would be collapsed and tear away at the ends, where they are joined to the element casing. Then there would be unfiltered flow at all times. The filter's outer casing can also rupture from the high pressure if it isn't controlled.

I've never heard of a pleated-element spin-on filter that does not have a bypass valve. Of course there are some made, once again for specific applications. As you can see, it's pretty important to have one because otherwise we would see many burst filter casings, and even the best-built elements would be torn thru on the first startup if they couldn't let some of the cold 90+psi oil go around the element. To obviate a bypass valve in a full-flow filter it could have a very open media that allows high flow of cold oil, but that would be let a lot of small particles go by. With a medium of a given area, resistance to flow is in direct proportion to filtration efficacy. So you could increase the size of the media, but to present very low restriction under all operating conditions the filter's size would become unwieldy. So the compromise in design is to have more medium area folded up and packed into a small casing, and protect it with bypass capability.

In fact, I looked up these filters on Manns website, and the main difference between the 719/5 and /12 is that the /5 has a 2.5 bar bypass, while the /12's is 1bar. That means the correct filter for the wbx allows oil to begin bypassing the element at only 15psi! With a reasonably tight engine at highway rpms, where it should raise at least 35psi OP, that valve would be fully open and good portion of the oil would not be being filtered at all! So much for full-flow filtering.

By the way, I have on my bench right next to that Mann a slightly-used FRAM Tough Guard cut open. It has the same features, anti drainback and bypass valve. It differs mainly in the construction of the pleated element and the bypass valve:

Compare the Mann element casing above to the Fram element. The Mann has the pleated media bonded to a metal casing, whereas the Fram's media is glued to cardboard endcaps. Both, as I said, have a perforated metal sleeve inside that supports the media against collapse. It would be tempting to say that the glued construction is a very poor way to build this, but provided factory quality control is decent, it's not much of an issue so long as the bypass valve does its job of keeping strain on the media within limits. But, QC and the methods to do this do vary from source to source. Both types of element construction are common, the metal type being moreso judging by some of the surveys I've seen.

You can see that the Fram bypass is separate from the element and instead housed in the spring riser that sits in the base of the outer casing (the Mann has a similar riser that I didn't show. These lay in the bottom of the casing and keep the element pushed up against the endcap). Unlike the Mann, the Fram has a filter screen around its bypass valve, so it does some filtering (albeit quite coarse) when in bypass mode, whereas the Mann just lets the bypass flow go by unimpeded.

Other filters bypass by having a coil spring under the element instead of the leaf-spring riser. When pressure is high, the entire element is pushed down away from the endcap and allows flow to bypass the element.

With a flashlight, you could probably see the bypass valve thru the center opening of most filters, except for the ones that spring-load the element itself.

Now, this gets me to the operating difference of different filters, and the big question around here: why do people who get an oil pressure warning with a hot-running wbx report that switching to the Mann filter makes them get the warning less often, or makes it stop altogether?

Well, it's not magic. Allowing that the inlet holes present more than adequate flow area, and the drainback diaphragm doesn't restrict flow around it, both of which are givens with most of the available designs, there's only three factors here that influence the volume of oil that can transit the filter with a given oil weight, temp, and pressure: fineness of filter medium (average pore size), surface area of the media, and the opening pressure of the bypass valve, or combinations of these three.

Here are two links to one of many places on the internet where you can see benchtop studies comparing a variety of spin-on filters that are on the market:
http://www.knizefamily.net/minimopar/oilfilters/index.html
http://www.knizefamily.net/minimopar/oilfilters/german.html

The second one includes some German filters. Parts of the comparisons, however, are pretty dated, and not only the specifications but the actual sources of these filters could have changed since then.

But, in that study, the Mann 719/5, which on the Mann website is identical to the /12 in overall canister size and mounting type so presumably has a similar-sized element inside, has 285 sq.inches of medium area. The Fram Tough Guard (not Extra Guard!) has 248. Not a big difference in area, but we don't know the relative avarage pore sizes of their media, and we can't compare the opening pressures of their bypass valves.

The main thing to keep in mind, though, in that oft-reported scenario with the warning buzzer is that the real problem is that the OP is marginal, not that the wrong filter is being used. Engines with healthy oil pressure are able to work past the slightly higher restriction caused by a filter with smaller media area, or finer media, or both.

If you take a look at the Knize comparison and follow his links, your head will swim with the myriad details of measurable aspects of various filters, and be surprised at how many appear to be exactly the same products made in the same factories but relabelled. Unfortunately, few of the comparisons on the web are actual studies, as it would take deep pockets to run filtration and flow analysis on these products. They are for the most part analysed under SAE specifications, but the tests are paid for by the manufacturers and the results are closely held. In addition, few on the web include non-American-made filters in their comparisons.

Anyway, if you want to waste a few hours of your life, explore the links above. Here's the Mann website as well:

http://www.mann-hummel.com/mf_prodkata_usa/index.h...kToPage=11

Wed Aug 27, 2008 12:41 pm

Chris-

Thanks for that excellent, informative reply. I tried a few times to access the Mann website myself, but it times out. Maybe it's something on my ISP or my computer.

Let me summarize a few of the points you made and see if I've got this right-

Vanagon owners shouldn't be worried about anti-drainback valves because the filter is mounted mostly upright anyway. And just because we don't see the ADBV at the top doesn't mean that it's not there.

The other difference that many Vanagon owners worry about is the bypass valve. The correct filter allows oil to bypass the filter at a very low pressure, so that's why switching from a Fram or STP to the Mann makes the OP light go off if it were on- oil is now bypassing the filter.

Thanks to your post, I think I've got it!

Here's a quote from Dennis Haynes, from the Vanagon mailing list, who answered my post on that list:

"The difference is the bypass not anti drain back valve. Both do have the
flap type anti drain back valve on top. If you look at the oil filter
adapter on most in VW line you will see a ball. The ball is held in place
by a spring. This is the bypass valve. The Water boxer does not have this
so it has to be in the filter. Most after market filter companies
incorporate this feature. That is why most aftermarket uses the same
filter number for both applications."

One other thing to note: I found a cross-reference list on germanfilters.com. It lists the Fram cross reference to the Mann W719/12 as a PH2991 or PH 3600. I could only find the latter online. Other books in the auto parts stores list the PH2870A. This makes me wonder if the by-pass valve of the 3600 or 2991 is closer in specs to the correct Mann one than the 2870A, or if the 2870A.

Thanks again for the info.

Ed in CT

Wed Aug 27, 2008 12:47 pm

Sticky nomination!

Wed Aug 27, 2008 1:37 pm

erdonline wrote: Chris-

Thanks for that excellent, informative reply. I tried a few times to access the Mann website myself, but it times out. Maybe it's something on my ISP or my computer.

I found the USA catalog part of the site. I then found the 719/12 filter specs that I linked to directly above.

Then I opened their "dimensions" page, and entered the inner and outer diameters of the top o-ring, and 3/4-16 as the thread size. That returned over 100 filters, every one they made that could spin on and seal onto the wbx filter mount. I couldn't link that page directly here because it was the result of a search form. So some of the filters are bigger overall diameters, and so on, but I was able to find the two we were discussing and compare their data. The only ways they differed were in the bypass pressure, and the ADBV was a "2" on the /5 and a "1" on the /12. No notation as to what the difference would be, maybe it's type, maybe it's pressure (doubt that; what pressure?). Anyway, I didn't explore the site futher to find out.

Quote:
Vanagon owners shouldn't be worried about anti-drainback valves because the filter is mounted mostly upright anyway. And just because we don't see the ADBV at the top doesn't mean that it's not there.

No, the ADBV would always be visible thru the inlet holes of the OF, unless there's some other way of doing it that I'm unaware of. The rubber disc thing is the only type I've seen, although on that Knize comparison he said some of them were metal, but no close-up pictures of that type so I'm not sure what he meant by that.

Quote: The other difference that many Vanagon owners worry about is the bypass valve. The correct filter allows oil to bypass the filter at a very low pressure, so that's why switching from a Fram or STP to the Mann makes the OP light go off if it were on- oil is now bypassing the filter.

I believe that's what is probably going on, but without knowing the specs of the "wrong" filter to compare, especially the bypass opening pressure, it would be impossible to be sure. They key thing, in my mind anyway, is that if the filter makes a difference, it points to a problem in the engine, not the filter.

Quote: Here's a quote from Dennis Haynes, from the Vanagon mailing list, who answered my post on that list:

"The difference is the bypass not anti drain back valve. Both do have the
flap type anti drain back valve on top. If you look at the oil filter
adapter on most in VW line you will see a ball. The ball is held in place
by a spring. This is the bypass valve. The Water boxer does not have this
so it has to be in the filter. Most after market filter companies
incorporate this feature. That is why most aftermarket uses the same
filter number for both applications."

I think he and I are in agreement on that. The wbx has no built-in bypass valve, while the Type4 did. The wbx also relieves pressure after the OF, so the OF sees the full pump output without controls on peak pressure. It is 100% full-flow as built.

Quote: I found a cross-reference list on germanfilters.com. It lists the Fram cross reference to the Mann W719/12 as a PH2991 or PH 3600. I could only find the latter online. Other books in the auto parts stores list the PH2870A. This makes me wonder if the by-pass valve of the 3600 or 2991 is closer in specs to the correct Mann one than the 2870A, or if the 2870A.

I'd sure like to see Fram's bypass pressures to compare. I haven't hunted for them but I kinda doubt they're available as easily as Mann's were. I suspect that the Mann bypasses more easily than the equivalent Fram, but without the data it's hard to know.

Quote: Thanks again for the info.

Ed in CT

Hope it makes things a tiny bit clearer. The misinformation around this issue has long been one of my pet Vanagon peeves.