When I installed a Racor 500 diesel fuel filter 6 years ago, the factory filter was a 2 micron size. In looking at replacements for the filter element at West marine, I now have to make a choice between 2, 10 and 30 micron filters. It seems like the logical choice would be the 2 micron again as that would provide the greatest filtering and cleanest fuel, but perhaps the downside is that fuel flow can be blocked more easily. Is there any thought (probably not a consensus) of whether a 2, 10 or 30 filter element is the best replacement for San Francisco Bay sailing with generally clean fuel from a gas station fuel pump and is there any reason to change from the OEM size of 2 microns? Thanks!
2 or more Microns for diesel fuel filter?
- Thread starter Dave 85 Catalina 30
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Primary & Secondary?
Fuel comming from the tank could be filtered at the 10 or 30 micron level, but then fuel continuing on into the high pressure pump should be filtered at the 2 micron level.
Fuel comming from the tank could be filtered at the 10 or 30 micron level, but then fuel continuing on into the high pressure pump should be filtered at the 2 micron level.
Dave...
I run a 2 mic Racor with a vacuum gage. A thorough tank cleaning and a double polishing of the fuel (when taken out of and put back into the tank) has kept the needle below the yellow zone all last season on a filter that was starting to draw a vacuum before the cleaning. I'd rather replace the filter than an injector or the high pressure pump. I carry spare 2 and 10 mic Racors "just in case"...
I run a 2 mic Racor with a vacuum gage. A thorough tank cleaning and a double polishing of the fuel (when taken out of and put back into the tank) has kept the needle below the yellow zone all last season on a filter that was starting to draw a vacuum before the cleaning. I'd rather replace the filter than an injector or the high pressure pump. I carry spare 2 and 10 mic Racors "just in case"...
dual filters
The only way to do what Dave j suggests is to routinely do the fuel polishing he described and monitor the vacuum guage. Absent either of these two actions, you run the risk of prematurely clogging the primary filter because of the small pore size. The filtering scheme recommended by marine diesel experts and the engine mfgs is to use a 2 micron filter only as a secondary filter; the primarly should be larger. I'm sure people do it differently with success but water entrained in the fuel can more easily clog a 2 micron filter and since the primary is intended specifically to collect water and big chunks, the chance is greater this scheme will ultimately be problematic.
The only way to do what Dave j suggests is to routinely do the fuel polishing he described and monitor the vacuum guage. Absent either of these two actions, you run the risk of prematurely clogging the primary filter because of the small pore size. The filtering scheme recommended by marine diesel experts and the engine mfgs is to use a 2 micron filter only as a secondary filter; the primarly should be larger. I'm sure people do it differently with success but water entrained in the fuel can more easily clog a 2 micron filter and since the primary is intended specifically to collect water and big chunks, the chance is greater this scheme will ultimately be problematic.
Two filters
Total agreement with the two filters scenario. Most diesel engines, at least the Yanmars, come with a 2 micron filter between the lift pump and the high pressure pump. On my boat, I have a primary, which is a water seperator, and contains a 30 micron element. The secondary is a 10 micron. The final filter in the system is the 2 micron Yanmar, on the engine. While it may work fine, and apparently does, I would not be comfortable with a setup with a single 2 micron filter.
Total agreement with the two filters scenario. Most diesel engines, at least the Yanmars, come with a 2 micron filter between the lift pump and the high pressure pump. On my boat, I have a primary, which is a water seperator, and contains a 30 micron element. The secondary is a 10 micron. The final filter in the system is the 2 micron Yanmar, on the engine. While it may work fine, and apparently does, I would not be comfortable with a setup with a single 2 micron filter.
Thanks Dave... your question
posts answered my question. I have a Yanmar with the same set-up. So its 30 mic at the Racor... and 2 mic at the engine. They call the Racor the secondary filter... even though it's first in line? No wonder I have a hard time grasping the most simple concepts. Sometimes it just does not compute for this Frenchmen.
posts answered my question. I have a Yanmar with the same set-up. So its 30 mic at the Racor... and 2 mic at the engine. They call the Racor the secondary filter... even though it's first in line? No wonder I have a hard time grasping the most simple concepts. Sometimes it just does not compute for this Frenchmen.
Three fuel filters?
Where is that third filter located? On my old 2QM20 and now the new 3YM30 there are just two. I carry both 2 and 10 micron filters for both. Right now they are both 2-micron, the Racor and the little can on the engine. Twice between Lake Erie and North Carolina the engine stumbled and quit. Once was while entering a touchy Atlantic inlet the other in the Alligator river. But I still think I would rather have the clean fuel. It takes me less than thirty seconds to change and I do not have to worry about the "can". But true, the spares have to be very handy(in the nav table).
Where is that third filter located? On my old 2QM20 and now the new 3YM30 there are just two. I carry both 2 and 10 micron filters for both. Right now they are both 2-micron, the Racor and the little can on the engine. Twice between Lake Erie and North Carolina the engine stumbled and quit. Once was while entering a touchy Atlantic inlet the other in the Alligator river. But I still think I would rather have the clean fuel. It takes me less than thirty seconds to change and I do not have to worry about the "can". But true, the spares have to be very handy(in the nav table).
The probable most damaging particle for a diesel is ....
range of 20uM Fortunately most of the 'particles' in diesel fuel are soft/deformable particles and are the result of resins formed by fungals and bacteria in the fuel (Claudasporium Resinae - a fungus.... being the worst) If your boats fuel system was 'carefully' designed (most arent) There will be THREE filters in series: a 10uM --> a 2uM --> a small 2uM 'guard' filter mounted on the engine ... the 2uM 'guard filter' being there simply to retain any extruded particles that come from the preceding 2uM (Racor, etc). If your OEM system WASNT designed (check with the engine mfg. specs.) for 2uM final filtration ... DONT think that applying a 2uM in place of a 10uM is somehow 'better'. A 2uM filter will take 5 times the 'work' of a 10uM to operate .... and you may then put an unduly heavy load onto the lift pump diaphragm which will rapidly reduce the service life of the diaphragm. If you do change from 10uM down to 2uM ... the needed course to maintain the same operating pressure (w/r lift pump) is to increase the *SURFACE AREA* of the 2uM by a factor or FIVE .... a 2uM filter will flow at 1/5 the volume per equal pressure as a 10uM; therefore you 5 times the surface area to get back to the SAME operating pressure/vacuum. So if you do put a 2uM in where you originally had a 10uM you will get 1/5 the flow at the SAME operating pressure OR will need/get 5 times the pressure/vacuum to operate it. Also in nature (w/r to 'particles') there will be exponentially MORE smaller particles than larger particles, so again if you replace a 10uM with a 2uM you can expect radically shorter filter life. Regardless, .... most 'fresh' fuel is clean and relatively water free, most particles 'grow' inside your tank (agglomeration of smaller particles into larger and larger particles). The BEST advice I can offer is to about every 2-3 years .... get inside the tank and mechanically scrub the walls free of all the 'resins' that are formed. With a maintained and *clean* tank ..... there will be little need for Filters !!!!!!!!!!! Keep only the amount of fuel in your tank that you NEED plus some reserve, buy only 'fresh fuel' from a 'high turnover' source such as a depot that sells to 'watermen' ... or jug it in from a truckstop. 'Marina fuel" is usually ;'degraded', contaminated, full of water, etc. etc. etc. (and usually higher price than 'highway' fuel even that 'highway' fuel is taxed). If you HAVE to buy fuel from a Marina .... pour some FIRST into a clean clear glass, then hold the glassful between your eyeball and very strong light .... if there is ANY 'haze' or cloudiness .... simply go somewhere else as there is NO need to load your tank with contaminated/degraded fuel. Just remember that the 'standard' Racor filter element will only retain approx. 25 GRAMS of 'crud' before it 'chokes'. Keep your tank CLEAN, buy CLEAN fuel ... then you wont need to change the filters so often. Filter operation: use gages to monitor the operating pressure/vacuum across the filters. Put on a NEW filter, then run the engine at WOT wide-open-throttle and read the gage. when the gage reading later decreases significantly (check the flow vs. pressure/vacuum charts on the RAcor site .... go to Parker.com ---> 'marine' ---RAcor Div., etc. ) when the operating pressure gets close to the flow needs of your ENGINE at WOT (on the Racor flow curve) then change the filters. Dont wait until the filters 'plug'. The gage (and the 'chart') will let you know long before the filter 'plugs'. ;-)
range of 20uM Fortunately most of the 'particles' in diesel fuel are soft/deformable particles and are the result of resins formed by fungals and bacteria in the fuel (Claudasporium Resinae - a fungus.... being the worst) If your boats fuel system was 'carefully' designed (most arent) There will be THREE filters in series: a 10uM --> a 2uM --> a small 2uM 'guard' filter mounted on the engine ... the 2uM 'guard filter' being there simply to retain any extruded particles that come from the preceding 2uM (Racor, etc). If your OEM system WASNT designed (check with the engine mfg. specs.) for 2uM final filtration ... DONT think that applying a 2uM in place of a 10uM is somehow 'better'. A 2uM filter will take 5 times the 'work' of a 10uM to operate .... and you may then put an unduly heavy load onto the lift pump diaphragm which will rapidly reduce the service life of the diaphragm. If you do change from 10uM down to 2uM ... the needed course to maintain the same operating pressure (w/r lift pump) is to increase the *SURFACE AREA* of the 2uM by a factor or FIVE .... a 2uM filter will flow at 1/5 the volume per equal pressure as a 10uM; therefore you 5 times the surface area to get back to the SAME operating pressure/vacuum. So if you do put a 2uM in where you originally had a 10uM you will get 1/5 the flow at the SAME operating pressure OR will need/get 5 times the pressure/vacuum to operate it. Also in nature (w/r to 'particles') there will be exponentially MORE smaller particles than larger particles, so again if you replace a 10uM with a 2uM you can expect radically shorter filter life. Regardless, .... most 'fresh' fuel is clean and relatively water free, most particles 'grow' inside your tank (agglomeration of smaller particles into larger and larger particles). The BEST advice I can offer is to about every 2-3 years .... get inside the tank and mechanically scrub the walls free of all the 'resins' that are formed. With a maintained and *clean* tank ..... there will be little need for Filters !!!!!!!!!!! Keep only the amount of fuel in your tank that you NEED plus some reserve, buy only 'fresh fuel' from a 'high turnover' source such as a depot that sells to 'watermen' ... or jug it in from a truckstop. 'Marina fuel" is usually ;'degraded', contaminated, full of water, etc. etc. etc. (and usually higher price than 'highway' fuel even that 'highway' fuel is taxed). If you HAVE to buy fuel from a Marina .... pour some FIRST into a clean clear glass, then hold the glassful between your eyeball and very strong light .... if there is ANY 'haze' or cloudiness .... simply go somewhere else as there is NO need to load your tank with contaminated/degraded fuel. Just remember that the 'standard' Racor filter element will only retain approx. 25 GRAMS of 'crud' before it 'chokes'. Keep your tank CLEAN, buy CLEAN fuel ... then you wont need to change the filters so often. Filter operation: use gages to monitor the operating pressure/vacuum across the filters. Put on a NEW filter, then run the engine at WOT wide-open-throttle and read the gage. when the gage reading later decreases significantly (check the flow vs. pressure/vacuum charts on the RAcor site .... go to Parker.com ---> 'marine' ---RAcor Div., etc. ) when the operating pressure gets close to the flow needs of your ENGINE at WOT (on the Racor flow curve) then change the filters. Dont wait until the filters 'plug'. The gage (and the 'chart') will let you know long before the filter 'plugs'. ;-)
The idea is very simple, folks:
Just like sandpaper, use progressively finer filters as the fuel approaches the engine. Using just a 2 micron filter can lead to issues, as water molecules are larger than 2 microns and will not pass through. This is good, because water can kill the injection pump and the injectors. This is also bad as water in the fuel will cause a shut down when the the 2 micron doesn't pass it. As we all know, engines shut down at the worst of times...like when you need them! If you have two filters, then I would suggest a 10 or 20 micron first, then a 2 micron at the engine. If you run three filters, then go with 30 or 20, then 10, then 2.
Just like sandpaper, use progressively finer filters as the fuel approaches the engine. Using just a 2 micron filter can lead to issues, as water molecules are larger than 2 microns and will not pass through. This is good, because water can kill the injection pump and the injectors. This is also bad as water in the fuel will cause a shut down when the the 2 micron doesn't pass it. As we all know, engines shut down at the worst of times...like when you need them! If you have two filters, then I would suggest a 10 or 20 micron first, then a 2 micron at the engine. If you run three filters, then go with 30 or 20, then 10, then 2.
Ah Chris,,,,,
I think you should review the size of water molecules. They even pass through RO membranes.
I think you should review the size of water molecules. They even pass through RO membranes.
Thanks for the advice
Thanks for the lively discussion on correct filter size. I'm persuaded that a 10 micron primary (at the lift pump) and a 2 micron secondary (on the engine) is probably the way to go and I'm not losing anything by changing the OEM 2 micron on the secondary to a 10.
Thanks for the lively discussion on correct filter size. I'm persuaded that a 10 micron primary (at the lift pump) and a 2 micron secondary (on the engine) is probably the way to go and I'm not losing anything by changing the OEM 2 micron on the secondary to a 10.
I've used..
I've used 10 or 30 micron Racor filters, as primary filters, for about 15 years and the secondary is whatever the engine makers filter is, sometimes a 15-17 sometimes a 25 micron.
A 2 micron, as a primary, is a clog waiting to happen at the most inopportune time... 10 - 30 micron is more than fine for a primary and in the last fifteen years I've never had a fuel related problem on any of my engines..
I've used 10 or 30 micron Racor filters, as primary filters, for about 15 years and the secondary is whatever the engine makers filter is, sometimes a 15-17 sometimes a 25 micron.
A 2 micron, as a primary, is a clog waiting to happen at the most inopportune time... 10 - 30 micron is more than fine for a primary and in the last fifteen years I've never had a fuel related problem on any of my engines..
Chris, Fred is right.
A water molecule is less then 3 Angstroms across (Isn't Google great?). An Angstrom is 0.1 namometers snd a micron (micrometer) is 1000 nanometers, so a water molecule is less than 0.0003 microns across.
A water molecule is less then 3 Angstroms across (Isn't Google great?). An Angstrom is 0.1 namometers snd a micron (micrometer) is 1000 nanometers, so a water molecule is less than 0.0003 microns across.
5:1 is the normal magnification of pre to final filter ....
Almost the entire filtration industry uses/recommends a prefilter @ 5X the retention rating of the final filter, unless one performs specific particle distribution analysis. a 2uM final should be preceded by a 10uM, a 10uM final should be preceded by a 50uM. (Resinated filter paper, the most common for 'fuel filters' isnt made in 50uM so virtually all mfg. use the next smaller - 30uM). The typical 5:1 set will 'usually' gain maximum service life in both filters. If the selection is correct, then the target is to have BOTH the pre and final filters fail/choke at the SAME time due to debris loading - the typical 'dirt capacity' of the nominal Racor type filter is approx. 35-50 grams (each). This assumes that the retention efficiency (or Beta ratio value - the log of influent to effluent wt% of particle vs. particle size) of the filter material is approx. equal in the finer and coarser filter media. The 'beta ratio' selected so that a minimal % of particles of next in series filter rating are retained in the PRECEDING filter.... eg. - in a 10uM-->2uM set, the 10uM filter will retain a % of 2uM particles. So, unless your tank is shedding a lot of large particles of rust, sand, feathers, etc. your 30uM filters are probably not doing very much in 'protecting' your final 2uM filters.
Almost the entire filtration industry uses/recommends a prefilter @ 5X the retention rating of the final filter, unless one performs specific particle distribution analysis. a 2uM final should be preceded by a 10uM, a 10uM final should be preceded by a 50uM. (Resinated filter paper, the most common for 'fuel filters' isnt made in 50uM so virtually all mfg. use the next smaller - 30uM). The typical 5:1 set will 'usually' gain maximum service life in both filters. If the selection is correct, then the target is to have BOTH the pre and final filters fail/choke at the SAME time due to debris loading - the typical 'dirt capacity' of the nominal Racor type filter is approx. 35-50 grams (each). This assumes that the retention efficiency (or Beta ratio value - the log of influent to effluent wt% of particle vs. particle size) of the filter material is approx. equal in the finer and coarser filter media. The 'beta ratio' selected so that a minimal % of particles of next in series filter rating are retained in the PRECEDING filter.... eg. - in a 10uM-->2uM set, the 10uM filter will retain a % of 2uM particles. So, unless your tank is shedding a lot of large particles of rust, sand, feathers, etc. your 30uM filters are probably not doing very much in 'protecting' your final 2uM filters.
10 Micron
Just installed the Racor duel fuel filters. The dealer said that Racor recommends 10 micron filters. That is what I use.
Just installed the Racor duel fuel filters. The dealer said that Racor recommends 10 micron filters. That is what I use.
Rich..??
Rich,Quote:"So, unless your tank is shedding a lot of large particles of rust, sand, feathers, etc. your 30uM filters are probably not doing very much in 'protecting' your final 2uM filters."
I've owned many different engines over the years and each manufacturer, save one, has told me the factory filter is anywhere from 15 to 25 micron not a 2 micron. For my current engine I have been told this by both Joe J. and Bob B. the Westerbeke engineers. Some of the Universal/Kubota's have an on-engine filter of 25 micron and some Westerbeke's as small as 15-17 micron.
Rich,Quote:"So, unless your tank is shedding a lot of large particles of rust, sand, feathers, etc. your 30uM filters are probably not doing very much in 'protecting' your final 2uM filters."
I've owned many different engines over the years and each manufacturer, save one, has told me the factory filter is anywhere from 15 to 25 micron not a 2 micron. For my current engine I have been told this by both Joe J. and Bob B. the Westerbeke engineers. Some of the Universal/Kubota's have an on-engine filter of 25 micron and some Westerbeke's as small as 15-17 micron.
Great Minds?
Maine Sail; I spent about an hour last night trying to find the micron size for the Kubota filters for my Universal M25XPB, with the same result as yours! If anyone has the correct info. please post. Thanks Fair winds Dave
Maine Sail; I spent about an hour last night trying to find the micron size for the Kubota filters for my Universal M25XPB, with the same result as yours! If anyone has the correct info. please post. Thanks Fair winds Dave
Kubota and Racors
The RACOR FUEL FILTER NUMBERS From the Racor 220/225R Spin-on Series Manual: R24S 220R, 2 micron replacement element R24T 220R, 10 micron replacement element R24P 220R, 30 mciron R26S 225R, 2 micron R26T 225R, 10 micron R26P 225R, 30 micron S - 2 micron; T - 10 micron; P - 30 micron As I recall from being in the store on Monday, the 15 series is a much thinner (shorter) filter. The manual covers two different separators, the 220R and 225R. 220R is for 30 gph, the 225R is for 45 gph, I'd bet we have the 220Rs. The Kubota engine spin-on filter is either a 2 ro 10 micron (don't know for sure), with these comps: NAPA 3390, Purolator PER-262-F, Fram P-3726, Kubota 7000-4308(1), Universal 298854,fleetguard # ff5226
The RACOR FUEL FILTER NUMBERS From the Racor 220/225R Spin-on Series Manual: R24S 220R, 2 micron replacement element R24T 220R, 10 micron replacement element R24P 220R, 30 mciron R26S 225R, 2 micron R26T 225R, 10 micron R26P 225R, 30 micron S - 2 micron; T - 10 micron; P - 30 micron As I recall from being in the store on Monday, the 15 series is a much thinner (shorter) filter. The manual covers two different separators, the 220R and 225R. 220R is for 30 gph, the 225R is for 45 gph, I'd bet we have the 220Rs. The Kubota engine spin-on filter is either a 2 ro 10 micron (don't know for sure), with these comps: NAPA 3390, Purolator PER-262-F, Fram P-3726, Kubota 7000-4308(1), Universal 298854,fleetguard # ff5226
Very unstable filter marketplace with lots of sleight of hand....
This is going to be similar to the typical untruthful lawyer's definition: "you need to know the definition of what 'IS' is", and "I did not have SEX with that woman" (without defining what SEX is). The simple answer is 10µM .... but thats a problem in itself. Filter manufacturers dont make the resinated paper filter media. The world supply of such technical resinated paper is essentially dominated by ONE company - Ahlstrom of Finland; with this worlds domination of a single source, the Chinese are entering the market ... and we all know how 'honest' the Chinese are. All the 'ratings' of this particular filter media is entirely 'arbitrary' .... called 'nominal' ratings in ":filter-speak" Resinated filter paper is rated at arbitrary 'nominal' ratings. A filter made of resinated paper will NOT remove ALL particles at their 'rating'. The 'good' manufacturers have a high efficiency removal at the 'rating' - Parker/Racor, Wix, Fram, etc. will remove 97-98% of the particles at the 'rating'. Others not as precise may be at 85-90% (by wt.%) efficient and still have the same 'rating'. Even with a well made and defined filter a 2uM rated filter by the 'ratings' definition of 'nominal' can pass a basketball sized particle and if the total weight % is gained and still be called a 2uM filter. A 2uM *nominal* rated (and at high efficiency) filter will 'approach' ALL particles removed .... at 10uM (*absolute* rating); this difference between nominal and absolute ratings are what drives the filter engineers (and engine manufacturers) absolutely NUTS ... and the reason you get varied answers. Only 'membrane' filters can be made accurately and can be offered as 'absolute' rating. Resinated paper filters simply cant be made that accurate, are nominally rated (% removal). Other. Fuel oil under the 'right' conditions will last hundreds of years. Most 'small' tanks are easily contaminated (fungals & bacteria), have a large (oil) surface to atmosphere ratio ... and in the presence of air/atmosphere can begin to decompose (polymerization, oxidation, etc.). If your tank is clean, the fuel that you take onboard is clean the nominal 10µM filter will probably be the correct to use. If your tank is fouled, the fuel is contaminated .... fungals/bacteria ... plus the fuel breaking down as various alkenes, then use a 2µM (but with much larger surface area as the particle load will be exponentially larger than if clean). Why 2µM? -- removal of the 'fractions', etc. that do not burn well !!!!! degraded oil doesnt burn well in the combustion chamber, the hot liquid unburned particles will 'blow right through' and will tend to deposit in the exhaust manifold and 'coke' on the hot surfaces. Caution- most of these 'small' particles are 'soft/deformable' so if you run a high differential pressure across the 2µM filter ... a lot of these particles will be 'extruded' through the filter. "Clean' oil doesnt do this to the degree as fouled oil. So, the simple answer is: 10µM but you need a clean tank to do this, and should be putting only clean oil*** into the tank ... and then buy your filter from a 'reputable' manufacturer --- Parker/Racor, Wix, Fram, etc. (I'd avoid buying (re-branded or 'private label') filters from the engine manufacturer !!!!) 2uM if your tank is contaminated, have degraded fuel in the tank .... and can then expect your filter usage to increase by a factor of 5X or 10X ... plus you have to increase the surface area to compensate for the 'work' (differential pressure across the filter) done or you risk breaking your lift pump diaphragm and or begin to 'extrude' the particles through the filters. ......... and the REAL message is clean out the tank on a regular basis, get those deposited resins (from bacteria and fungals - colonies/bio-films or 'calcyx') off the tank walls by mechanical scrubbing. This will produce less 'nucleation sites' onto which particles GROW and 'agglomerate' into larger and larger particles. *** clean oil = holding a clean glassful of oil between your eyeball and strong light shows NO haze or 'cloudiness'. If the oil is 'crystal clear' and has no haze then its particle load 'distribution' is probably less than 1-2uM. If the tank oil is 'dark', has a haze or is 'cloudy' --- take it home and burn it in your home heating system, clean the tank thoroughly .... and start all over. Then you wont need to so heavily depend on 'filters' ... they only 'catch' (to a %) whats sent to them. The 'best' is an independent onboard recirculation polishing system ... removes the crud before it 'agglomerates', keep the tank cleaner longer, keeps the 'particles' in the tank to low levels .... and if you do break off a large chunk of tank wall crap the high 'turnover rate' (typically 2-3gpm/100 gal.) will QUICKLY restore the particle distribution IN the tank back to near zero and at 'submicron' sizes ..... all results in the main-line fuel system is hardly ever challenged with particles. BTW ... the term 'micron' became obsolete about 30 years ago. the Correct term is 'micrometer' ... when I hear/see the term 'micron' I immediately think of someone who doesnt know what they are doing. hope this helps.
This is going to be similar to the typical untruthful lawyer's definition: "you need to know the definition of what 'IS' is", and "I did not have SEX with that woman" (without defining what SEX is). The simple answer is 10µM .... but thats a problem in itself. Filter manufacturers dont make the resinated paper filter media. The world supply of such technical resinated paper is essentially dominated by ONE company - Ahlstrom of Finland; with this worlds domination of a single source, the Chinese are entering the market ... and we all know how 'honest' the Chinese are. All the 'ratings' of this particular filter media is entirely 'arbitrary' .... called 'nominal' ratings in ":filter-speak" Resinated filter paper is rated at arbitrary 'nominal' ratings. A filter made of resinated paper will NOT remove ALL particles at their 'rating'. The 'good' manufacturers have a high efficiency removal at the 'rating' - Parker/Racor, Wix, Fram, etc. will remove 97-98% of the particles at the 'rating'. Others not as precise may be at 85-90% (by wt.%) efficient and still have the same 'rating'. Even with a well made and defined filter a 2uM rated filter by the 'ratings' definition of 'nominal' can pass a basketball sized particle and if the total weight % is gained and still be called a 2uM filter. A 2uM *nominal* rated (and at high efficiency) filter will 'approach' ALL particles removed .... at 10uM (*absolute* rating); this difference between nominal and absolute ratings are what drives the filter engineers (and engine manufacturers) absolutely NUTS ... and the reason you get varied answers. Only 'membrane' filters can be made accurately and can be offered as 'absolute' rating. Resinated paper filters simply cant be made that accurate, are nominally rated (% removal). Other. Fuel oil under the 'right' conditions will last hundreds of years. Most 'small' tanks are easily contaminated (fungals & bacteria), have a large (oil) surface to atmosphere ratio ... and in the presence of air/atmosphere can begin to decompose (polymerization, oxidation, etc.). If your tank is clean, the fuel that you take onboard is clean the nominal 10µM filter will probably be the correct to use. If your tank is fouled, the fuel is contaminated .... fungals/bacteria ... plus the fuel breaking down as various alkenes, then use a 2µM (but with much larger surface area as the particle load will be exponentially larger than if clean). Why 2µM? -- removal of the 'fractions', etc. that do not burn well !!!!! degraded oil doesnt burn well in the combustion chamber, the hot liquid unburned particles will 'blow right through' and will tend to deposit in the exhaust manifold and 'coke' on the hot surfaces. Caution- most of these 'small' particles are 'soft/deformable' so if you run a high differential pressure across the 2µM filter ... a lot of these particles will be 'extruded' through the filter. "Clean' oil doesnt do this to the degree as fouled oil. So, the simple answer is: 10µM but you need a clean tank to do this, and should be putting only clean oil*** into the tank ... and then buy your filter from a 'reputable' manufacturer --- Parker/Racor, Wix, Fram, etc. (I'd avoid buying (re-branded or 'private label') filters from the engine manufacturer !!!!) 2uM if your tank is contaminated, have degraded fuel in the tank .... and can then expect your filter usage to increase by a factor of 5X or 10X ... plus you have to increase the surface area to compensate for the 'work' (differential pressure across the filter) done or you risk breaking your lift pump diaphragm and or begin to 'extrude' the particles through the filters. ......... and the REAL message is clean out the tank on a regular basis, get those deposited resins (from bacteria and fungals - colonies/bio-films or 'calcyx') off the tank walls by mechanical scrubbing. This will produce less 'nucleation sites' onto which particles GROW and 'agglomerate' into larger and larger particles. *** clean oil = holding a clean glassful of oil between your eyeball and strong light shows NO haze or 'cloudiness'. If the oil is 'crystal clear' and has no haze then its particle load 'distribution' is probably less than 1-2uM. If the tank oil is 'dark', has a haze or is 'cloudy' --- take it home and burn it in your home heating system, clean the tank thoroughly .... and start all over. Then you wont need to so heavily depend on 'filters' ... they only 'catch' (to a %) whats sent to them. The 'best' is an independent onboard recirculation polishing system ... removes the crud before it 'agglomerates', keep the tank cleaner longer, keeps the 'particles' in the tank to low levels .... and if you do break off a large chunk of tank wall crap the high 'turnover rate' (typically 2-3gpm/100 gal.) will QUICKLY restore the particle distribution IN the tank back to near zero and at 'submicron' sizes ..... all results in the main-line fuel system is hardly ever challenged with particles. BTW ... the term 'micron' became obsolete about 30 years ago. the Correct term is 'micrometer' ... when I hear/see the term 'micron' I immediately think of someone who doesnt know what they are doing. hope this helps.
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