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Old 03-07-2016, 11:33   #1
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Change secondary fuel filters if primary is 2 microns?

Hi,
I am using 2 micron primary fuel filters. The suction gauges say they are as good as new.

My genset and engine have a recommended interval for replacing their secondary fuel filters.

Should I follow this recommended interval, given that the primary should catch everything?

I certainly want to baby these engines and not be penny wise and pound foolish. But I don't want to be completely foolish and make busy work by replacing what should be pristine filters.
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Old 03-07-2016, 11:56   #2
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Re: Change secondary fuel filters if primary is 2 microns?

I use 2 micron primaries in Racor housings. My secondaries never get any debris. I use to cut them open to check. I change my main secondaries once a year that is about 500 hours. The generators get changed every other year. The primaries will catch some water that gets thru the Racors. The mains circulate 75 gallons an hour (mains use 8/hr) and at 500 hours the vacuum gauge reads about 5-7" after circulating 35,000 gallons.
I only buy fuel from stations that service commercial boats and sell a high volume of fuel. Once the tanks were clean, I haven't had fuel problems.
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Old 03-07-2016, 12:32   #3
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Re: Change secondary fuel filters if primary is 2 microns?

What Lepke said. Except I may wait a couple of years on the secondary since I don't use the engine much

I believe the factory recommendations don't take into account the pre-filters.

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Old 03-07-2016, 13:28   #4
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Re: Change secondary fuel filters if primary is 2 microns?

Once wet, the filters have limited life. Oil is a solvent too. You replace the secondaries as if there were no primaries. You can stretch things somewhat off course but not wildly so.

If a filter collapses, it is a mess. If the secondary does, you are buying a new hp pump.

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Old 03-07-2016, 13:56   #5
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Re: Change secondary fuel filters if primary is 2 microns?

I've got a Racor 2 micron and water spinner as a primary, and then the great big paper filter as a secondary. It's easy to inspect a Racor and see that stuff is or isn't building up, but you can't see what going on in the secondary without destroying it. My answer is to replace the secondary when I replace the primary. It's not like we're talking about a major part of a boat budget, and I'd much rather replace filters than replace injectors.
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Old 04-07-2016, 09:05   #6
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Re: Change secondary fuel filters if primary is 2 microns?

Yes, you'll be amazed to see small amounts of sediment in the secondary, I change every year, they're cheap insurance.
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Old 04-07-2016, 09:26   #7
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Re: Change secondary fuel filters if primary is 2 microns?

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Originally Posted by barnakiel View Post
Once wet, the filters have limited life. Oil is a solvent too. You replace the secondaries as if there were no primaries. You can stretch things somewhat off course but not wildly so.

If a filter collapses, it is a mess. If the secondary does, you are buying a new hp pump.

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^this. I'm doing mine every other primary change out.
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Old 04-07-2016, 13:47   #8
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Re: Change secondary fuel filters if primary is 2 microns?

I'm in agreement with puffcard, "every other primary change out." My reasoning is, why have secondaries if I think they are doing nothing except adding expense?
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Old 04-07-2016, 15:42   #9
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Re: Change secondary fuel filters if primary is 2 microns?

I must admit I'm somewhat amazed at the use of 2 micron filters anywhere on a sailboat. I did a lot of research on this early this year because of all the boaters using 2 micron filters.
Of the top brands of filters (WIX being #1) that produce secondary filters (the one on the engine if it has one) for nearly every marine diesel made I could not find one below 10 micron. Why, because that meets the design specs of the manufacture. 10 micron is equal to 0.0004 inches. The average human hair is about 0.004 or 10 times larger. As a ASE Master Tech and GM Master Tech I am test certified on modern common rail electronic diesel engines. The 2015 GM Duramax 6.2 engine idles at approximately 4,800 psi fuel pressure and wide open throttle produces over 29,000 psi. The reason for such high fuel pressure is the size of the openings in the injector are so small (GM will not disclose the actual spec) that it takes these pressures to push the fuel through them. Yanmar fuel pressure, about 3,000 psi max. I point this out because the Duramax fuel filter spec is 7 micron and it is the only filter installed. It is also the water separator.
I have a Racor R20T (10 micron) on my Yanmar 4JH3 and R12P (30 micron) on my Northern Lights genset with WIX 10 micron secondary on each. I also use biocide every time.
I would really like to know why those using a 2 micron on a sailboat are doing so.
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Old 04-07-2016, 16:03   #10
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Re: Change secondary fuel filters if primary is 2 microns?

Hmmmm have you all stuffed the words Primary and Secondary?

I think the Primary filter is the one on the engine. The Racor is the Secondary even though its in the first position, before the Primary.

Is this correct?

Anyway, I often have the Racor with a 2micro filter as well as the one on da engine. So then u change the engine one every second time I change the Racor.



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Old 04-07-2016, 16:47   #11
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Re: Change secondary fuel filters if primary is 2 microns?

Quote:
Originally Posted by buzzstar View Post
I'm in agreement with puffcard, "every other primary change out." My reasoning is, why have secondaries if I think they are doing nothing except adding expense?
Because the secondary was the ONLY filter the engine manufacturer installed.

Quote:
Originally Posted by msponer View Post
Hi,
I am using 2 micron primary fuel filters. The suction gauges say they are as good as new.

My genset and engine have a recommended interval for replacing their secondary fuel filters.

Should I follow this recommended interval, given that the primary should catch everything?

I certainly want to baby these engines and not be penny wise and pound foolish. But I don't want to be completely foolish and make busy work by replacing what should be pristine filters.
How many hours are you talking about? On each engine? HP? GPH?

Quote:
Originally Posted by MarkJ View Post
Hmmmm have you all stuffed the words Primary and Secondary?

I think the Primary filter is the one on the engine. The Racor is the Secondary even though its in the first position, before the Primary.

Is this correct?


A "convention" that seems to have been adopted, at least in the 18 years I've had my boat and been reading boating forums, the first filter is the primary.

The primary usually is a water separator, too, which usually isn't installed on the secondary engine mounted filters.
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Old 04-07-2016, 17:08   #12
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Re: Change secondary fuel filters if primary is 2 microns?

Primary is the first filter the fuel encounters. It is nearly always a water separator (filter) by design as well. It's main job is to stop the water and "big" stuff that would clog the secondary filter quickly. There is no reason in the world to have a "primary" filter stopping smaller "stuff" than the secondary filter. That said, the filter element has a useable life which is generally 2 years regardless of fuel flow and may begin to come apart. Nearly everything I've read and my training shows 2 years max. You can go longer but YOYO (you're on your own). Filters are cheap (BTW, never buy the cheapest filters, WIX or similar are best), your engine is worth a good one... just say'n
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Old 04-07-2016, 19:15   #13
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Re: Change secondary fuel filters if primary is 2 microns?

Quote:
hat said, the filter element has a useable life which is generally 2 years regardless of fuel flow and may begin to come apart.
Can you provide a link to data supplied by filter manufacturers? It is a new concept to me, and I find it very surprising.

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Old 04-07-2016, 22:15   #14
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Re: Change secondary fuel filters if primary is 2 microns?

Quote:
Originally Posted by onewadd View Post
I must admit I'm somewhat amazed at the use of 2 micron filters anywhere on a sailboat. I did a lot of research on this early this year because of all the boaters using 2 micron filters.
Of the top brands of filters (WIX being #1) that produce secondary filters (the one on the engine if it has one) for nearly every marine diesel made I could not find one below 10 micron. Why, because that meets the design specs of the manufacture. 10 micron is equal to 0.0004 inches. The average human hair is about 0.004 or 10 times larger. As a ASE Master Tech and GM Master Tech I am test certified on modern common rail electronic diesel engines. The 2015 GM Duramax 6.2 engine idles at approximately 4,800 psi fuel pressure and wide open throttle produces over 29,000 psi. The reason for such high fuel pressure is the size of the openings in the injector are so small (GM will not disclose the actual spec) that it takes these pressures to push the fuel through them. Yanmar fuel pressure, about 3,000 psi max. I point this out because the Duramax fuel filter spec is 7 micron and it is the only filter installed. It is also the water separator.
I have a Racor R20T (10 micron) on my Yanmar 4JH3 and R12P (30 micron) on my Northern Lights genset with WIX 10 micron secondary on each. I also use biocide every time.
I would really like to know why those using a 2 micron on a sailboat are doing so.
Thats interesting re Duramax filter micron rating. I was under the impression the 2 micron filters came about because of the high pressures in common rail injection systems. But whats the drawback in filtering to 2 microns? apart from possible waste of $$ Thanks for yr input onewadd.BTW I've cut open a couple of very old fuel filters ( over 10 years sitting) with no visible signs of disintegration but not a big enough sample to be sure that it doesnt happen but I certainly arent going to chuck mine out after 2 years
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Old 05-07-2016, 05:34   #15
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Re: Change secondary fuel filters if primary is 2 microns?

In regard to usable life of diesel fuel filters, many manufactures recommend 500 hrs or two years. My training at GM was the same until, with the advance of electronics, filter life was calculated by the Engine Control Module. Now based on many factors it could be longer or shorter.
The most important part for ALL diesel engines is that fuel not only runs the engine but is the cooling and lubricating element for the high pressure pump. While restricted fuel flow will eventually shut down your engine, there can easily be excessive wear or even damage in the high pressure pump before there is enough restriction for shutdown.
While we debate the use of a 2 micron filter (I'm guessing some believe that is to protect the system better) the engineers that designed the system are saying that 10 micron is all that is needed before entering the high pressure system.
You can find on the Racor/Parker web site (I found it during my research, you can too) that they recommend no more than 10 micron for a primary filter and in higher flow engines or smaller filters using 30 micron. Their reasoning is the 2 micron is overkill and will begin to restrict flow much sooner. And of course you should have the 10 micron secondary right before the high pressure system.
A diesel lives on fuel flow and the smaller the filtered particle stopped by a filter the faster it is filled up and restriction begins (this cannot be seen by cutting one open). If you have ever had to replace a high pressure pump you know how expensive it can be.
I believe in delivering as much fuel as easily as possible to this very important and expensive part of my diesel and that the designers should know it best. Two aspirin are good when you have a headache, but half the bottle???
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