The CAV Filter - pre-amble

Its very strange - I set out to have a real good look at pre filtration for small engines, really on the basis that I was not too happy with the head layout of the old cav filter - in terms of potential for trapped air.

I then end up thinking I may as well keep it !

I never really had a problem with them for leaking - or difficult maintenance - in fact, they are always easier to undo than many a spin on type oil filter. Also - the more you look - if you do want a clear bowl, then even those units have seals to the bowl and seals to the head. All spin on types destroy the fuel line integrity - and need re-bleeding once new filters are fitted.

Its a sorry tell of woe it seems on many forums that folks seem to be unable to service these things - or move them to a better position ? The plastic drain bung swells and leaks ! - well maybe buy a metal one and a new washer ( about £3 ! ) If you can't reach it - move it ! We are not talking oil tanker here - we are talking teeny little unit attached with 8mm hose !

Also - people talk of filters suddenly blocking. You need a pretty crappy tank to suddenly block a primary filter - or a very poor maintenance schedule. Air in the line - Yes, I see that one.

The layout of the head does bug me though. Seems a lot of dead space high up to trap air.

Seals don't leak if they are positoned correctly and are new - but trapped air bugs me ! That can stop you - at least I 'feel' it can. How you 'feel' is important on boats, Its not a rational pastime !

It is right what I said about the variety of filters available for the M16 x 1.5 spin on head - but we are still limited to a basic range of ( absolute) filtration of 7-10 - or 20 - 30. You do of course have the 'strainer' option, @ 60 micron - if you felt the neeed to add an extra unit ( maybe a bad steel tank, not easy to remove or service )

Micron 's - Ha - now I have learned a bit, I laugh at all the forum comments on this - all nonsence !

At least Fleetguard will specify - when they choose to - to a 98% rating.

They might say, for the same filter, 10 micron at 90% - 15 micron at 98%. The 15 is the 'absolute' rating - and to some extent the one that matters ( if we are talking - we don't want any 17 micron bits at all ) - but where it gets complex is when one starts to add - and we only want a certain % of the 5 micron particles - that make up 15 % of the total impurities in the supply - and at a certain flow rate !

Mann-Hummel rate their filters to 3 micron - @ a certan %. ie Same filter specs - Fleet - 7 micron@ 90% - Mann - 3 micron @ 70% - easy really !

They are also set out to confusing differing standards to fool people into thinking the are finer than they actually are - I supect !

So - when your Champion says 5 micron they mean, well 5 @ 50%, but 12 @ 90 - oh and 15 if 99% !

Actually - the old cav, for its application - ie pre filter for small diesel engine is just about spot on for capacity and micron size.

Fleetguard make both types - which is I think unique, usually it one or the other with no mention that they are different. This is why I like Fleetguard - the 296 is a very basic old filter, but they care enough to make both types.

FF167 - Filter type ( Flow rate 50 litres/hr 18 microns at 98% and 10 microns at 80%) - this the 296 cav type - filter, flat top - larger central tube area - perforated, not solid. ( Mahle example shown here )

FF167A ( Flow rate 75 litres/hr 12 microns at 98% and 10 microns at 92% ) - more common agglomerator - lots of holes on top and solid tube through the middle.

( the figure in brackets are from Fleet G Tech - from a third party )

I always thought of the latter ( this is the 'normal' Delphi type ) as being 'less' fine than the other type ?

So - after looking and searching for just about every filter unit available - I am almost full circle back to Cav - with myabe a Fleetguard FF167a fitted. It does fit the bill !

I am tempted by the FS19599 ( fit a spin on M16 head ) - its a dedicated water separator ( built in drain etc - and central drip tube ) - its slightly finer 7 micron @ around 90% plus - its also the modern Stratapore filter media. The spin on head has less joints - has an option of built in primer - and has a much cleaner head section in terms of bleeding the thing - and its only £11 for a head, and the filter is £5.

But - I have the glass bowl with CAV - which I like, but actually since its in the engine bay it should be a metal one ! So - we are back with the spin on !

I just wish Fleetguard made a dedicated water separator, as the FS19599 - in Stratapore, at 12 - 15 micron ! They don't - next best is the FF5135 - a cellulose filter ( with a drain tap ) at 21 micron @ 98%.

Even the Fleetguarrd spin on range - and their expensive heads ( 1 x 14 un ) - with Racor type bowls - are treated cellulose. As are the Racors ! There are Stratapore 25 micron elements - but I supect they are slowly being phased in - without too much notification unless one asks ! After all - make a new 'better' medium and every one wants that - you then have 25 million cellulose filters to get shot of worldwide that no one wants any more !

Commerce - hugh.

If you don't want a clear bowl - may as well go spin on - drain all included ?

If you want a clear bowl - the cav is fine.

Anyways - read all this crap - this page and the longer one. You may give yourself some ideas. Its a minefield of bad info and marketing hype out there - and difficult to really find anything simple and concrete on the subject.

Interesting link here to an article oin the Hurley Owners site.

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