View Full Version : Diesel Fuel Filters
04-27-2011, 08:19 AM
On Monday I went to change the fuel filters for my Yanmar 3GM30F engine. The Racor primary filter the I use is sold at the local West Marine store. I purchased one and happened to look at the label and noticed that is said 2 mircon. This is the same filter I've been using for years. I went on-line to the Yanmar site and looked up the engine mounted secondary filter and found it is rated at 10 microns. This would explain why I've never seen even the slightest bit of dirt on the secondary filter every time I've changed it.
So this time I changed the primary (2 micron) filter and left the secondary (10 micron) filter along. Opinions please: Was this a mistake??
-Racor does make the same primary filter element in 20 micron, it is not stocked at the local West Marine Store, I'd have to order it.
-Both the primary and secondary filter elements have never had any signs of dirt or sludge on them. Typically I have, in the past, been changing them after 50 to 60 hours
04-27-2011, 10:13 AM
Actually Racor makes 2, 10 and 30 micron filters, at least for their 500MA and 500FP series filters. A 2 micron is a bit small for the primary in that it will plug up very quickly if/when you get some cruddy fuel or your tank cruds up. I generally use a 10 micron primary.
As far as not changing the secondary at 50-60 hours, I think you will be fine particularly if the primary wasn't dirty when you changed it. A quick google search yields a 250 hour change interval for fuel filters on marine engines. So I expect that you will be fine decreasing the interval on the on-engine filter. I would change it if you found significant crud on the Racor filter though.
04-27-2011, 11:59 AM
My thoughts are pretty much the same as yours. I was surprised to discover that the primary filters I've been using for at least 20 years have been only 2 micron. As I was surprised to find out that the secondary filters have been 10 micron.
BTW I have a Racor 200 Series filter and according to the Racor website elements are available in 2 and 10 micron.
04-27-2011, 01:53 PM
I think you need to put the fuel through the 10 mic filter first, then the 2 mic. This is how two stage filtration works, with the finer filter downstream of the coarser one. If the coarse follows the fine, any particle that gets through the primary will not be stopped by the secondary, and will be allowed to enter the injector pump.
Some mechanics would disagree with your short change interval as well, , arguing that a filters performance is improved by some "cake" on the filter media.
The change interval is best judged by suction effort as read on a vacuum gauge, not hours of use.
04-27-2011, 02:33 PM
I agree with those who say that the primary (water separator) fuel filter should have a larger effective aperture than the secondary (usually engine mounted) fiter. I use a Racor R20T water separator filter, feeding the engine mounted Yanmar fuel filter, on my 4JH3 engine. Maybe I've been lucky, but I have never had a filter clog in the water separator filter. The R20T is a 10 micron element. From Torrenson Marine:
The lower the micron rating, the finer the filtration. Lower micron ratings should be considered when there is no additional downstream filtration.
Follow your engine manufacturer ft.s recommendation for fuel filter micron rating.
S = Secondary/Final 2 micron (Brown cap)
T = Primary or Secondary/Final 10 micron (Blue cap)
P = Primary 30 micron (Red cap)
04-27-2011, 02:47 PM
kapnd - I agree in an ideal world the primary should be 10 micron and the secondary 2 micron. However the Yanmar engine mounted filter is 10 micron, with no other choices listed. My primary is available in either 2 or 10 micron.. No choice of anything coarser than the secondary.
Norman - I'd check the micron rating of your Yanmar engine mounted filter, it might very well be 10 micron, the same as your primary. IE it may be doing little or nothing. In 30 years of boating with diesel engines (over 20 years with Yanmar engines) I also have never had a primary filter clog. This has been with a 2 micron primary filter.
04-27-2011, 06:53 PM
I have a vacuum gauge that screws into the top of the Racor 500 ( threw the T handle away). It is SLICK!! Got about 700 hours before the needle moved.
Also, like you, my filters are in the incorrect sequence.
Lotsa hours without a problem.
Are there Yanmar filters available from second-party providers? As everybody has commented above, the normal thing is for the water separator/primary filter to be larger mesh than the secondary. I'm a little surprised that Yanmar thinks that 20micron is suitable for a primary filter, but, there you have it.
I don't find engine hours to be a useful approach to filter change. I think they should be changed once per year, no matter what. What gives a schedule and way to look at the fuel, and be able to see if there's bacterial slime (black, smelly). Beyond that, the differential pressure gauges found on Racor filters are very good. Without a pressure gauge, gallons of fuel burned might be the best measure. If you're just idling around at low power, particularly with a low-bypass injection system like a Yanmar, you're barely filtering any fuel at all.
One company I worked for, as engineer running GM 16-149 engines, the Racors were changed at 5Lbs of pressure differential, or after burning 10,000 gallons of fuel, whichever came first. With clean fuel, the boat running all the time, it would run out the hours without showing any pressure difference. If I was drawing fuel from a tank that had bacterial slime in it, the Racor might clog up to 5Lbs of differential in 4 hours.
My first-ever diesel engine was on an old Cat D4 crawler. The fuel cap was a big heavy brass casting with the advice
Buy clean fuel
Keep it clean
was cast into the top. Good advice.
04-28-2011, 09:31 AM
I don't know about the Yanmar filters, but I just ordered fuel and oil filters for my Perkins. Some internet seaching revealed Fram and Carquest part numbers for the same filters. You can go into a good auto part store and ask them to search. They should be able to find matching parts. I find that If I order in bulk, six at a time, they are cheaper than store bought by a couple of dollars each, even with shipping. As for the Racors, I found them cheaper on ebay.
04-28-2011, 05:36 PM
Seo - Yanmar doesn't say anything about a 20 micron primary filter. They just supply a 10 mircon secondary filter and, I guess, leave it up to the owner what if anything is used in the way of a primary.
Johnsandusky - I haven't been unable to find aftermarket filters for my Yanmar. So unless I can come up with something I'm going to stick with the 2 micron Racor primary and the 10 micron Yanmar secondary. In spite of being bass acwards it has worked for over 20 years for me.
The CAV filters that are used on Perkins are very common. No surprise that aftermarket people are making filter elements for them.
04-28-2011, 07:08 PM
Was this a mistake??
Rich H, the poster, is someone who consults to people who design filtration systems and is a long distance sailor. There is probably no one on the net who knows more about filtering diesel fuel.
See also my simplified recirculating filtering system (designed with Rich's help) that has worked very well over two seasons.
04-29-2011, 08:58 AM
In reading the post by RichH it looks to me as though my system is what he recommends. He states that the prefilter (Racor) should always be smaller the the engine mounted "guard" (Yanmar"). The only problem he describes is the additional work the lift pump must do with a 2 micron prefilter, that could lead to failure. Following is what he wrote:
"The 'engine guard' is there simply to protect the engine if the Racors (10ÁM or 2ÁM) fail (filter pleats break, etc.) or begin extrude very small soft/deformable particles. The engine 'guard' should ALWAYS have a 'prefilter' upstream protecting it, and the prefilter for the 'guard' should alway be SMALLER in ÁM retention than the 'guard'. You 'guard' is probably rated at 10ÁM (95%-97%)"
Or am I missing his point?
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