Thread: oil filters again......Td5

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.

Would it be right in saying also, that due to the way the centrifuge operates, that it filters the same be it new or 3/4 full and so there isn't a gain to change it too often.

Also, with centrifuge filtering, is it still beneficial to change the oil at more regular intervals than that recommended due to oil breakdown etc, but just leave the old filters in there.

G'day Ben, 'bout time you found your way in here !

AFAIK, Delphi make the ERR3340 filter (not Coopers), so they may have the contract for the TD5 full flow filter as well.

Originally Posted by Slunnie

Would it be right in saying also, that due to the way the centrifuge operates, that it filters the same be it new or 3/4 full and so there isn't a gain to change it too often.

Also, with centrifuge filtering, is it still beneficial to change the oil at more regular intervals than that recommended due to oil breakdown etc, but just leave the old filters in there.

Slunnie, depends on the oil and the operating conditions. Using a full synthetic oil helps.
My experience using Delvac 1 in a TD42T Patrol (indiect injection) used for lots of towing (2500kg) is that the oil is barely stressed at 20,000km using an OE Nissan combo filter (part by-pass, part full flow) and a Donaldson Synteq media full flow (Beta 2=6, ie. 50% efficient @ 6 micron in the applicable multi-pass test ISO test)
No additive depletion, viscosity stable (no thickening or thinning) and some wear metals lower than a mineral oil @ 5000km.

I'm in agreeance with Isuzurover re filter intervals. The longer you leave a filter in place the better it filters in terms of partical size but the worse your flow rate at a given pressure. The exception to this is the oil bath type air filter and the oiled foam filters as they deposit the trapped gunk out of the air flow they suffer minimal degredation.

If you have the luxury of being able too having your oil examined you can work out the best servicing intervals for your style of driving. I got the chance while at a major filter suppliers to see a single batch of oil that had been run too gross over contamination and sampled every 10 hours. They then showed me some rough things you can do to approximate your oils contamination. (Amazing what a carton of beer can achieve after hours)

The first and simplest test is a vertical run test on paper. get about 2-3ml of engine oil (after running the engine to normal temp) in a pippet dropper and some a4 gloss paper (photo quality printer paper)

Stand the paper just shy of vertical (call it 75-80 degrees)and drop the oil just shy of the top. Watch the oil run down the sheet and it will deposit its contaminants as it runs down the page. The oil should roll down the page in the same way a dozer track rolls over the ground but the paper will retain a little oil as it passes.

If your oil is still carrying black crap when it stops running down the page then its about time for a change. This will vary with all the usual suspects (temp, oil quality, viscosity, water/diesel contamination etc etc.)

Dave

"In a Landrover the other vehicle is your crumple zone."

Originally Posted by Slunnie

Would it be right in saying also, that due to the way the centrifuge operates, that it filters the same be it new or 3/4 full and so there isn't a gain to change it too often.

Also, with centrifuge filtering, is it still beneficial to change the oil at more regular intervals than that recommended due to oil breakdown etc, but just leave the old filters in there.

Slunnie - you are correct - The centrifuge is not really a filter, and does not operate as such. From the results I have seen they operate at a constant efficiency (unlike a filter), regardless of when the cartridge is changed. The only problem would be if the cartridge was allowed to fill completely, but if you change at the manufacturers interval that should never happen.

As Rick mentioned above - "oil breakdown" almost never occurs with synthetic oils, it can happen with non synthetics, however not usually to any extent over the recommended service interval. The biggest problems with keeping oil in an engine too long are usually (1) wear metal buildup (2) soot buildup, and (3) acid buildup.

Having a bypass centrifuge keeps the soot and wear metals down, and with modern diesel, there shouldn't be much of an acid buildup (unless you only do short trips). However changing the oil does get rid of the contamination from your oil like no filter or centrifuge can.