Thread: The Air Filter Poll

1 @ unifilter on defender

1 @ std paper filter on disco

1 @ oil bath on swb

i think the unifilter will be going unless i can find a positive i dont know about yet.....

am looking into buying the prefilter socks for those dusty trails....

I have a K&N filter just on the end of the intake pipe on my rangie but I will be changing it to a UNIFILTER inside a custom airbox with a snorkel as soon as funds and time allow. The reason i will go the UNI is that 1 my dads friend owns unifilter and my dad has run them for years in all sorts of vehicles and has never had a problem.

Thomas

Donaldson Main and Pre filters on the 110 and a cyclone. Has done 320k km and still runs like new (and uses no oil). The main filter doesn't get changed until the pressure indicator pops up to say the filter is full of dust - it is actually bad for your engine to change the air filter too frequently.

The IIA has a hilux filter box with a finer filter. In my defence I bought the finer filter before I worked in filter R&D, and didn't know any better. It will be replaced by a donaldson element - the FF element is free to anyone silly enough to use it.

Originally Posted by incisor

1 @ unifilter on defender

1 @ std paper filter on disco

1 @ oil bath on swb

i think the unifilter will be going unless i can find a positive i dont know about yet.....

am looking into buying the prefilter socks for those dusty trails....

Geez Inc, don't you remember mine and isuzurover's (who is a filtration engineer) rant's against oiled foam and oiled cotton gauze filters ?

http://www.aulro.com/afvb/showthread...ght=air+filter

A couple of isuzurovers quotes from this thread http://www.aulro.com/afvb/showthread...ght=air+filter

Maybe I can shed some light on the filter changing issue.

Contrary to popular belief, most filters do not work like sieves, air filters not at all, and oil/fuel filters only slightly. Conventional filters capture particles by inertial impaction, interception, and diffusion (brownian motion) - although the latter plays almost no role in oil/fuel filters.

As a filter traps particles, those collected particles assist in filtering further particles from the air stream, so filters will become MORE EFFICIENT (at capturing particles) the more particles they collect. There is a corresponding increase in pressure drop, however this is always linear, whereas efficiency increases are initially more logarithmic (increase very rapid at first).

So for air filters, the best thing you can do for engine longevity is to leave the filter changes as long as possible, and only change the filter when pressure drop becomes too high. 110 countys with 3.9L ISUZU engines have a large twin element donaldson filter, with a big sticker "do not service (change) element to frequently" and "change element only when pressure drop reaches set level". So not only are you wasting money, you are actually harming your engine by changing the AIR filter too frequently.

Oil filters are slightly different. Most modern full flow filters are only able to remove particles down to about 5 microns at best, since they have to retain a high flow rate and minimal pressure drop. They will also increase in efficiency over time, but if the pressure drop gets too high, the flow will bypass the filter. However sticking to manufacturers service intervals should be fine.

Bypass centrifuges (like the TD5 has) are capable of removing particles down to about 20 nanometres (0.02 microns). This means they are able to remove soot, and other small particles which the full flow filter cannot remove (which contrary to popular belief do cause engine wear).

All engines with bypass centrifuges have much longer service intervals than engines without, as the centrifuge keeps the oil clean for much longer. If you have an engine without a centrifuge (e.g.) 300TDi, changing your filter won't really help much, only changing the oil, as the soot and small wear particle buildup is the problem - retrofitting a bypass centrifuge or bypass filter would be even better.

So changing your filters too frequently won't really help engine longevity, and coule even harm it

Incidentally - oiled foam, oiled cotton or oil-bath filters are very poor filters in comparison to a good quality fibrous (cellulose) filter.

Originally Posted by rick130

Geez Inc, don't you remember mine and isuzurover's (who is a filtration engineer) rant's against oiled foam and oiled cotton gauze filters ?

i do thats why i am looking to change it :P

G'day Ben, hope you don't mind me quoting you like that.

And if anyone is silly enough to want to use a K&N that fits a Defender 300Tdi housing, PM me, only 20,000km use 5 years ago before I went back to Doanldson and Fleetguard elements.

Originally Posted by incisor

i do thats why i am looking to change it :P

well what's with the bloody poll then ??

there had been a bit of chatter about filters and it prompted me to do the poll as it would be nice to see whats being used and whats not...

but it has done nothing but get me roused on so far...