Secondary fuel filter ?

John T · Oct 20, 2009

Most boats have both a primary and a secondary fuel filter. When you have two, the one on the engine becomes the secondary and the filter between the tank and the engine is the primary. The mechanical fuel lift pump on the engine is sufficient to draw fuel through both filters. Since fuel flow is low on these engines, the Racor 110 or 120 filters are more than adequate.
Some captains replace the mechanical fuel pump with an electric automotive type, so take a look at the archives for the discussion.

RichH · Oct 20, 2009

Choose wisely w/r the 'micron rating' of the filters. The 'primary' (first in the series) should be ~5X larger in µM than the 'secondary' (next in series). The engine mounted 'guard filter' should be LARGER in µM rating than the 'secondary'.

Typical for most boats using Racor available filter ratings:
30µM---->10µM---->15µM (engine guard).
OR .....
If you have very large SURFACE AREA filters 10µM----->2µM------15µM (engine guard)

The 15µM engine guard will 'choke' when 'slugged' with an overabundance of small µM particles ... its there in case one of the 'upstream' filters breaks its pleats, etc. Change the engine mounted 'guard' as often as you change the primary/secondary.

RichH · Oct 20, 2009

jrpla said:
Thanks, John, Rich

Rich, the Yanmar 2gm filter is rated 10-15micro

Following your recomendation then the primary filter (Racor) should be the biggest available, the 30micro

is this correct?

The engine mounted Yanmar guard filter is 'usually' at 15-17µM ....

If you have ONE filter in addition to the engine mounted guard filter, then use a 10µM
: .....10µM ---> 15µM (guard)

If you have TWO filters (primary AND secondary), then use a 30µM, followed by a 10µM BEFORE the 15µM engine mounted 'guard' filter.
: ..... 30µM Racor--->10µM Racor ---->15µM guard

Ron20324 · Oct 20, 2009

Sorry, but I have to disagree with Rich. I wonder where he got his info? The engine company that sets up new engines for dealers and maintains many of them in the Annapolis area said, in a diesel engine maintenance seminar, in response to a question about the micron size, said a 2 should only be used if you have an electric pump. Other pumps just do not have the suction. This was all covered in a thread earlier this year.

In Nigels Caulders book, he suggests 10 to 30 in the primary, 7 to 12 in the secondary. "In certain special applications, it may be as small as 2 microns".

Ron20324 · Oct 20, 2009

In a thumb-thru of the West book, I see only 2/10/30 filters, so I'll have to take someone's word for it if they have a 5/15/21 or whatever else size they say they have. Having previously cited a reference book and a person who does diesels for a living (so I would consider him to be a professional), I would only wonder why you would put in a 30Pri and ALLOW anything smaller to get to your next filter (a 10 ?) and clog it, too? Why not just put the 10P in there in the first place? With a 30P and a 10S, it could just be possible that both could become clogged at the same time (as in rough seas), and maybe drive you nuts trying to figure which was the problem, not to mention taking longer to get the engine running again. I don't recall if it was a book or an article that said if the 30 (or larger) gets clogged, then you really need to be cleaning the fuel tank, the source of the dirt. Also recall reading some (if not all) engines can tolerate small dirt going through the combustion process ( Not stating that as fact, but I'm sure I read it somewhere ).

While I suppose there are cases where you KNOW your fuel is dirty and have decided to live with it (in the middle of the ocean, let's say), sure you could put in a 30P, then a 10P, then a 5S to gradually weed out the dirt. So, as I ponder, why not just put in the 10 primary and stop it all right there? Yeah, it will get dirty- they ALL get dirty- but that's why people put in filter-transfering valves- like in another post currently running. I use a 10Pri and a 10Sec in mine. Me, I'd avoid a 30 and/or a 2.

And I'm confused as to Rich calling the final/last line of defense filter a secondary, but also refering to a "guard" filter. Are they one and the same?

Ron McCoy · Oct 20, 2009

Our local Hunter dealer on the Chesapeake Bay receives new boats from the factory with the Yanmar 2 micron filter on the diesel itself - this is the secondary filter. The primary filter is a Racor brand. Depending on the size of boat, Yanmar engine, the primary filter is either a 110 or 120 on smaller boats (up to 30-34 ft). On larger boats you'll see the factory install Racor 230 or larger (cannister type filter). Some boats come with the Racor 500 turbo systems. Regardless of the model Racor filter, the primary filter provided by Hunter is a 30 micron. Granted, these new boats have clean fuel tanks that aren't gummed up with sludge.
I try to keep my tanks clean and the fuel fresh. I have an Algae X fuel polisher along with a Racor 500 turbo using a 30 micron filter. I don't have engine problems. BTW. Change all your filters every fall and you'll be ready next spring when the weather warms.

Steve Dion · Oct 20, 2009

The 2GM can handle a primary 10 or 30 micron filter without any problem. This is easy to do. You can find the filters on the internet or at West Marine or any other marine shop. I used the Racor 120 for my 3JH2E. Do not use a Racor 110 they are NOT water seperators. The larger filters are actually cheaper to replace the elements.

RichH · Oct 21, 2009

Ron20324 said:
Sorry, but I have to disagree with Rich. I wonder where he got his info? The engine company that sets up new engines for dealers and maintains many of them in the Annapolis area said, in a diesel engine maintenance seminar, in response to a question about the micron size, said a 2 should only be used if you have an electric pump. Other pumps just do not have the suction. This was all covered in a thread earlier this year.

In Nigels Caulders book, he suggests 10 to 30 in the primary, 7 to 12 in the secondary. "In certain special applications, it may be as small as 2 microns".

I'm currently leaving on a long passage to 'de islands' and dont have time for a comprehensive technical reply .... of why your presenter at the seminar has either innocently mislead you etc., you misunderstood (as boat/fuel filtration is not the simple entity as it first seems), etc. etc. Certainly neither your presenter nor Nigel Caulder would ever have the filtration technical data to back up their (often very misleading) 'claims'. 'Nuff said, ..... until I can get the quiet time for a detailed reply (and © it). Im a multidisciplined scientist/engineer whose primary focus in fluid and thermal sciences is filtration engineering; done so for the past ~35 years working for, consulting to, etc. etc. some the worlds leading filter manufactures, etc. etc. ;-)

VERY briefly, ... filters are sized not solely on the micrometer (µM) rating, but must be carefully sized for the *flow rate vs. differential pressure* (Q/∆P)... then choosing the correct 'effective surface area' so the Q/∆P condition are satisfied so that the normal service life (in lightly particle loaded fluid) is extended to a reasonable degree. For example all the 'tech data' for filter sizing/selection is available on the (as an example) http://www.launchrun.com/RacorCustomers/ParkerRacor.html website ... somewhat hard to find the Q/∆P curves, but they are there if you look for them.

So, with regard to a 2µM vs. a 10µM (and paraphrasing typical filter manufacturer's data) ....... at the same engine flow demand requirements ..... and filters at the same surface area: a 10µM will have 1/5th the flow resistance (operating differential pressure - ∆P) of a 2µM. To get the important Q/∆P value into the 'normal published range' of the manufacturers recommendation ........... one simply has to increase the SURFACE AREA of a 2µM by 5X that what was used by the 10µM. Then the important ∆P (at constant flow rate) across the 2µM (at 5 times the surface area of the 10µM) will be EXACTLY the same as the 1/5 smaller surface area of the 10µM !!!!! .... and one definitely doesnt need a booster pump to do it. If one somehow thinks that a direct replacement of 10µM for a 2µM (and without increasing the surface area) is valid, then the typical filtration engineering estimate calculation of 'in-service-life to plugging' is about 8 times LESS (you will need to change out the 2µM @~8 times more often than a single 10µM) !!!!!
The typical particle found in (dirty) fuel systems are usually soft and deformable .... so, run the filters at high differential pressure (changing a 10µM for a 2µM will do just that) and the filters will extrude a majority of the deformable particles through the filter until they finally 'choke'; AND given sufficient time many of the soft extruded particles will reform into larger particles downstream of the filter!!! IF (and a BIG IF) however, the filter is sized correctly by also including surface area considerations, a 5X 2µM surface area filter will last ****exactly as long**** as a 10µM and will have the exact same operating ∆P (but at higher cost). The 2µM at 5X the surface area will also NOT INCREASE the load to the lift pump in comparison to a (single) 10µM. That statement of needing a 'booster pump' is just 'nonsense' ... your presenter probably doesnt have the faintest clue about the filtration that he's applying, maybe he should attend a filtration seminar, huh? Maybe he should simply learn how to read (any) filter manufacturers simple published *flow vs. differential pressure* (Q/∆P) charts.

Further, fuel filters 'arent screen doors'. A 2µM 'rated' filter will pass hard particles MUCH larger than 2µM (to a repeatable % by wt.) and will also capture smaller particles than the 'rating'. Ditto the 10µM 'rated' and the 30µM ... they arent that 'exact'. No, such filters dont have uniform 'holes'; microscopically the spaces between the long cellulose fibers in the 'felting' may be 10 to 20 times the 'rated pore size' of the filter. Such fuel filtration is similar to 'using a bunch of sticks to filter golf balls' ... and you will never catch 'all' the golf balls.

THE important advice I can give when selecting fuel filters is: choose the LARGEST filter that is reasonably priced in accordance to your budget for: ... slower fluid velocity through the filter so the debris is captured ON the surface rather than deeply imbedded into the filter media - for longer in-service life and less deformable particle extrusion; more contact time for the (smaller) particles to ADsorb and adhere to the filter media; LOWER operational differential pressure; more 'dirt capacity'.
Racor's 2µM is in the range of 15µM on an 'absolute' or 100% removal efficiency basis, the 10µM at ~30+, ... and the 30µM is a 'rocks sticks and feathers' remover; BUT they do remove a lot of particles smaller than the 'rating'. Standard practice remains (unless one does extensive/expensive particle count distribution studies)..... the secondary should be 5 times smaller µM than the Primary; the (Yanmar) engine mounted 'guard' filter is ~15-18µM (95-97% removal efficiency) so dont 'futz' with the 'guard filter' just replace in kind/size/µM ... and 'the guard filter' should be totally ignored with respect to the 'usual' primary/secondary ... its simply a 'last chance filter' if all hell somehow breaks loose upstream.

.... and THE most important advice I can offer is: routinely clean out your tank so you dont grow particles IN the tank and then ultimately send those particles to the (expensive) filters.

I'll try to 'amplify/simplify' as I sail south and will post when I can find an occasional WiFi node.

(BTW - My consulting fee for advanced filtration engineering/consulting is $$$(unbelievable)/hour.)

shorty · Oct 21, 2009

30 Micron Racor

before my 3GMF per multiple mechanic's recommendations.

Bob S · Oct 22, 2009

Rich, where do I send the check

. These questions become redundant after a while but I always seem to learn from them. It's funny but the boat manufactures don't put a lot of thought into this. At least Catalina didn't. My 1995 C30 came with a Racor 2 micron as the primary with a 10 micron secondary mounted on the engine. Before reading this and previous posts I bought new filters. I've only owned the boat 2 seasons and replaced them before this season began. From what I read they should be good for about 5 years. (about 50 hrs/season) The Racor has a bowl and I check it frequently. No water or sediment and so far no problems.

It appears Catalina didn't put much thought into their design.

Stu Jackson · Oct 22, 2009

Bob S said:
It appears Catalina didn't put much thought into their design.

The micron thing has been beaten to death. The more important mistake Catalina made was to plumb the fuel pump before the primary fuel filter. Those OEM pumps have little filters on the bottom and they get clogged up if you don't correct the wrong factory plumbing. Should be: Tank to primary to pump to engine. It's an easy fix, requiring a few feet of fuel hose, a double ended barb and some hose clamps.

jibes138 · Oct 22, 2009

Sounds like a load of govno to me

I have a diesel pickup truck with 150,000 miles on it. It runs like the day I bought it. There is just one fuel filter in it. It has a large bowl with a filter in it that separates water and filters debris. I change it about every 20,000 miles and it is filthy when I change it. Filter is about 40 bucks. 80 bucks if you live in New England. Now I drive about an average of 60 miles per hour so each filter lasts about 330 hours. I think all you boaters should go to a ford dealer, get a filter bowl for a Ford 7.3 litre motor and install it on your boat. You will also get a nice heating coil in the bowl to heat up your fuel for cold weather operation. Maybe rotating your fuel regularly matters more than the filters? Assuming I go through 30 gallons a week that is as much as my boat uses in two seasons. I think the tanks in our boats should be about 5 gallons so we would always be using fresh fuel and a single jug would fill it up.

RichH · Oct 24, 2009

Stu Jackson said:
The micron thing has been beaten to death. The more important mistake Catalina made was to plumb the fuel pump before the primary fuel filter. Those OEM pumps have little filters on the bottom and they get clogged up if you don't correct the wrong factory plumbing. Should be: Tank to primary to pump to engine. It's an easy fix, requiring a few feet of fuel hose, a double ended barb and some hose clamps.

Putting the pump BEFORE any filter set is the PROPER and most efficient way to do any fuel system. Its all a matter of simple hydrodynamics. Only in 'cheap and dirty' boat installations does one find such a pump in vacuum motive service ... because its the CHEAPEST way to do the hook-up.
A single stage pump working in vacuum service will totally stall (cease flow) at about 6"hg vacuum (about -2 psi) while taking the same pump and putting it in pressure service can develop upwards of 25-30 psi. That means that a vacuum driven system will totally stall from delivering fuel at a very low differential pressure across any filter set .... and you essentially are throwing away 'mostly unused' filters that have a low of more capacity as most RACOR SYSTEMS are designed for 30 psi PRESSURE feed ... and the filters themselves are built to withstand ~75 psid 'burst differential'. If you look at the common flow/differential curves from any manufacturer you will see that you can deliver 15X the fuel at an 'emergency' differential of 30 psid than at ~2psid.

The typical 'cheap and dirty' boat system vacuum system is composed of copper tube (reactive with diesel fuel), contains 'compression fittings' (ultimately loosen and suck air) .... the only benefit is that if the system develops a leak the system will automatically shut down by sucking air instead of filling the bilge with oil.
A pressure feed system, found on almost all automotive, most commercial marine, aircraft, boiler and prime mover feed .. are all pressure feed - with stainless tube, double faired connections, etc. - inotherwords 'robust' and equal to the system design. The system is and must be 'bombproof' against fuel leakage. With pressure feed you usually include a 'strainer' (50-100µM stainless mesh) to protect the pump.

Filter-wise, a pressure feed system will more tend to deposit debris ON the surface of the filter media (dirt filtering dirt), whereas a vacuum system will tend to draw the debris very deeply INTO the filter media with a resultant very short service life of the vacuum mode filter.

I think you have to ask yourself the question ..... if almost ALL other fuel systems depend on pressure feed, why do they install such systems in boats as vacuum feed? The probable answer is .... the boat builder doesnt have to make any piping modifications to the engine set (cost consideration), can install the cheapest components possible for his/her contribution of the installation, less liability if the extremely unknowledgeable 'consumer' (poor maintenance) loads the fuel into the bilge and into a waterway (and the builder is ultimately responsible). I believe the boat builder chooses to allow a boat to be wrecked as a total loss due to 'clogged filters' / fuel blockage than to pay the costs of a major eco clean-up; as, the monetary risk is less with a wreck than a major eco-event ... plus the original filter installation costs are extremely minimal.

Stu Jackson · Oct 24, 2009

Tank Filter Pump

RichH said:
Putting the pump BEFORE any filter set is the PROPER and most efficient way to do any fuel system. Its all a matter of simple hydrodynamics. Only in 'cheap and dirty' boat installations does one find such a pump in vacuum motive service ... because its the CHEAPEST way to do the hook-up.

I beg to differ. In this case on almost all older Catalinas, the fuel pump and the primary filters are right next to each other.

They just got it wrong and it has absolutely nothing to do with economics.

The fact that they are so close to each other make the reapir a piece of cake.

Brought to you by the same thought process that put filter screens on the inlet of the hoses inside the fuel tanks, and Catlaina wasn't the only manufacturer to make that dumb move, were they?

Secondary fuel filter ?

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John T

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