Wrong oil filter

[JackE]

I have got two Mann filters but they are different sizes one is w840/2 the other w719/12 both look like they would fit on the engine I.e. Same size fitting but I just wanted to make sure I was okay to use either or if there will be a problem? Many thanks here is a link to a picture I tried to put imagine in here but couldn't get it to work sorry https://docs.google.com/file/d/0B4fRTU4 ... cslist_api

[itchyfeet]

719/12

[JackE]

Cheers, would using the larger one cause any problems?

[itchyfeet]

Dunno but oil filters are more complex than just a filter, afiik they have pressure relief valves in event of being blocked so don't risk using the wrong one.

[ghost123uk]

A quick Google around finds that the other one is for the VW 1.9 "AHU" TDI engine as used in Passats etc (and retro fitted to some posh T25's)

[silverbullet]

840/2 for 5 pots?

[JackE]

Thanks for all your help. There is a lot more info in this post at the Samba http://www.thesamba.com/vw/forum/viewtopic.php?t=315559 somebody has cut open the oil filters to look at difference between them.

[silverbullet]

Useful to flag that post up.

So the 719/5 is a heavy-duty (low temperature conditions?) version that will stand a bigger pressure differential of 2.5 bar (36 psi) before bypassing, whereas the 791/12 will bypass at 1 bar (14.5 psi)

I will stick with the 719/12 because 1 bar pressure drop across a filter is a LOT of oil pressure to give a way and if the oil is that filthy, the engine has bigger problems imho.

[itchyfeet]

sb

Can you explain what you mean please, does the bypass happen if the pressure difference on either side of the filter is more than 1 bar? i.e. because filter is blocked

thanks

[silverbullet]

Thats how I read it. The bypass can only respond to a pressure differential between the pump and engine sides of the filter element.
When the oil is really cold then it wont want to flow through the element, there will be sufficient pressure drop to open the bypass valve.
Same conditions if the filter is choked with carbonized crud from a knackered engine pumping black treacle around...

[itchyfeet]

Interesting, so at startup every oil filter is probably on bypass so any crap picked up can get into the oil galleries
a good reason to change oil regularly and a benefit of a DJ oil warmer/cooler I'd say?

[California Dreamin]

I read the whole of that article ... yup indeed, one man's 'extensive & in depth' interpretation of how he believes an oil filter functions. On the whole he is correct, however, 'assumption is the mother of all screw up's'.
At one point he even questions himself saying 'I can't believe I wrote that' when someone quoted what he had previously written.

Point is: with a well maintained vehicle, the oil filter contains a massive pleated filter media surface area of 285 sq/inches. So I ask you, why is it that this guy and everyone who's commented so far, have made an automatic assumption that the media would offer too much resistance to the cold oil and presuming that it would by-pass continuously when driven from cold?
For starters..285sq/inches is a huge area of porous media for the oil to get through, I suggest so large as to easily cope with the flow rate from the pump & offer a fairly low resistance even with cold viscous oil.
I would also point out:
Nobody has even mentioned the oil pressure relief valve which automatically vents excess oil pressure back to the sump.
The oil by-pass valve is there as a 'fail safe' and predominantly opens 'if' the media gets blocked through neglect.
The By-pass valve might have a momentary lift now and again (if someone was to floor it on start) but I suggest that this would be rare and for fractions of a second.

It is also worth mentioning that all quality multi-grade oils contain detergent additives that were developed to keep microscopic sludge-forming solid particles in suspension. Anti-oxidation additives were also added to slow the formation of these sludge deposit precursors. The oil filter effectively sits there waiting for these 'suspended' solids particles to come around from the constant oil stream. These solids are a by product of combustion and the mixing of fuel/soot/water (from condensation), high temperature carbon deposits & other reactants. It doesn't really matter where in the process they occur, only that they don't form sludge which can block oil flow and so effective lubrication.
The main factors determining the 'amount' of sludge seem to be: stop/start driving (the engine rarely being up to its full running temperature which could burn off/boil off, much of this contaminate).
Cheaper and less capable lubricants, that do not have sufficient capability to internally clean and suspend these deposits.
Poor servicing regime.


Of course this is my interpretation but I ask you this: would VW really design a 'full flow' system that didn't actually filter its oil for much of the time whilst cold? of course not!

Martin

[HarryMann]

Correct Martin !
The W 840/2 is what i use on AAZ.. slightly larger version of the JX filter. Think it's a T4 diesel filter.