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Old 31-12-2020, 16:31   #1
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dumbest fuel filter question EVER.

The engine is a Yanmar 2gmf. I've mastered oil changes and am moving on to other maintenance and service issues one of these being changing fuel filters.



I'm trying to pre-order parts and discovering the difference between a T and an S filter gave me pause and questions. I'm not on the boat where the manual is and even if I could trace fuel lines from here I don't know if primary means first or most important. I looked at an online shop manual and it didn't give an answer. So without excessive preamble here's the dumb newbie question:


Which is the primary fuel filter? The separator and the bowl or the cartridge in the can with the star shaped screw retainer mounted to the engine itself?


TIA


Kurt
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Old 31-12-2020, 16:41   #2
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Re: dumbest fuel filter question EVER.

Quote:
Originally Posted by KayZee View Post
The engine is a Yanmar 2gmf. I've mastered oil changes and am moving on to other maintenance and service issues one of these being changing fuel filters.



I'm trying to pre-order parts and discovering the difference between a T and an S filter gave me pause and questions. I'm not on the boat where the manual is and even if I could trace fuel lines from here I don't know if primary means first or most important. I looked at an online shop manual and it didn't give an answer. So without excessive preamble here's the dumb newbie question:


Which is the primary fuel filter? The separator and the bowl or the cartridge in the can with the star shaped screw retainer mounted to the engine itself?


TIA


Kurt

Secondary is on the engine, primary is first in line from the tank.
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Old 31-12-2020, 16:53   #3
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Re: dumbest fuel filter question EVER.

And guessing that the primary is a Racor, a T filter is 10 micron (recommended) and S is 2 micron which most feel is too fine and prone to clogging.
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Old 31-12-2020, 17:01   #4
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Re: dumbest fuel filter question EVER.

Racor Fuel Filter Numbers

https://c34.org/bbs/index.php/topic,...3.html#msg5533
and


https://c34.org/bbs/index.php/topic,10681.0.html
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Old 31-12-2020, 17:06   #5
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Re: dumbest fuel filter question EVER.

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Originally Posted by Calif.Ted View Post
And guessing that the primary is a Racor, a T filter is 10 micron (recommended) and S is 2 micron which most feel is too fine and prone to clogging.

It is a racor and what's on there is an S. I had already figured out the difference but because the racor was an S model which is for, according to Racor, recommended for after a 10 micron, that's what opened up this rabbit hole of which was the primary and which was the secondary.


Thanks,


Kurt
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Old 31-12-2020, 17:09   #6
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Re: dumbest fuel filter question EVER.

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Originally Posted by Calif.Ted View Post
And guessing that the primary is a Racor, a T filter is 10 micron (recommended) and S is 2 micron which most feel is too fine and prone to clogging.

And if the S that's been on there for 2 years (about 60 hours) isn't clogging, would you change to a T or stay with an S?


thanks again,


Kurt
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Old 31-12-2020, 17:22   #7
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Re: dumbest fuel filter question EVER.

Quote:
Originally Posted by Calif.Ted View Post
And guessing that the primary is a Racor, a T filter is 10 micron (recommended) and S is 2 micron which most feel is too fine and prone to clogging.
Many years ago I would have agreed with the 2 vs 10 argument presented here. However, a well experienced boat neighbour asked me how would I know which filter is clogged if the primary is 10 and the secondary is 2? I have been using 2 and 2 ever since and have discovered that most mechanics agree with this logic. If the engine is starved for fuel and there is fuel in the tank, check the primary filter and change it. If it is a 2 micron filter, you are done and the engine should start. If is a 10 micron filter, you may need to change both filters before getting fuel into the injection pump (if bad fuel is the issue).

It can be worse. The 2 photos below show the remains of a paper towel left in the fuel tank by a mechanic that was supposed to polish the fuel and clean the tank. The decomposed towel fibres made their way into the little anti-water block device that Racor 500 filters use at the bottom of the housing. Pulling the ball out of the device revealed a significant mass of fibres. Fortunately we were able to figure out where the blockage was before changing the secondary filter which was still fine.
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Old 31-12-2020, 17:23   #8
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Re: dumbest fuel filter question EVER.

Iíve always used a 2 micron. Our fuel tank is clean, and when the engine is running turned over every 6 or so hours....free fuel polishing!
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Old 31-12-2020, 17:50   #9
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Re: dumbest fuel filter question EVER.

Yanmars engine mounted secondary filter is 10 micron according to the Yanmar rep (Dont necessarily believe reps but...)
That implies that that's all thats necessary but doesn't guarantee the perfect setup.
On our Yanmar I run 18 micron primary & 5 micron secondary, have no experience with 2 micron so cant comment on use. I can see marathon 1150's point.
2 micron will definitely clog quicker.
In your setup can't see whatever size of 2 or 10 micron you choose as mattering too much but thats just my opinion.
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Old 31-12-2020, 19:23   #10
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Re: dumbest fuel filter question EVER.

First, the OP's question is certainly not dumb. I know several people who argue that the filter on the engine is the "primary". Since it is the only fuel filter you must use. The other one is optional and not all Yanmars have one. And Yanmar doesn't help out - they don't use the word "primary" or "secondary" in the manual.

I have also gone to a 2 micron filter in my Racor 500 (which I'll call the secondary). On my 4JH4-HTE the primary is 5 micron. It's also 4 times the cost of a Racor filter cartridge and incredibly hard to change if the engine is hot.

I know this because in mid Gulf Stream at 3AM I had a filter blockage and engine RPM went to 800. I changed the Racor (whch takes 5 minutes in my boat) - no improvement. So I then spent 45 minutes fighting seasickness in a 100 degree engine room in 5 foot rolling sea draped over a hot engine replacing the primary - which, of course, fixed it.

So that I would never have to do that again, I switched to 2 micron Racor elements. I also have a pressure gauge on the Racor so I can tell if it's becoming even a little clogged.

My surprise is that I have not had more clogging with the 2 micron element. I routinely change my fuel filter when I change the oil at the Yanmar recommended interval for my engine of 250 hours. In five years with the 2 micron the pressure gauge has never gone into the "yellow" much less the "red" zone on the gauge - I've never had to change a filter early.

I believe the reason is that sailboat engines just don't use much fuel. The Racor 500 is rated for 60 GPH. My engine uses 1.5GPH. When I change it at 250 hours the element has filtered less than 400 gallons - or less than seven hours at full flow. If I owned a sportsfisherman that used 30GPH I bet I'd have clogged filters using 2 micron - and since 90% of Yanmars go into powerboats Yanmar doesn't recommend 2 micron in the primary.

The other benefit is that my secondary filter doesn't get dirty at all with a 2 micron ahead of it. So I only change it every two years now saving a few bucks. But - if you engine is less than 2 years old and still under warranty you might want to stick with Yanmar's recommendations so they don't get grouchy about approving a warranty claim.
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Old 31-12-2020, 20:38   #11
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Re: dumbest fuel filter question EVER.

Quote:
Yanmars engine mounted secondary filter is 10 micron according to the Yanmar rep (Dont necessarily believe reps but...)
That is my recollection also but I couldn't remember the source. I ran a 2 micron on a small Perkins because it was all I had on hand. It was only 100hrs./9 months and the only problem was the nagging thought "I wonder if 2 micron will clog ?"
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Old 01-01-2021, 03:31   #12
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Re: dumbest fuel filter question EVER.

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Originally Posted by KayZee View Post
Which is the primary fuel filter? The separator and the bowl or the cartridge in the can with the star shaped screw retainer mounted to the engine itself?
Not a dumb question, i have wondered this myself. And now that we have several others chiming in, i see that there is no right answer, cuz different people have different ideas of primary and secondary.

jon
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Old 01-01-2021, 08:14   #13
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Re: dumbest fuel filter question EVER.

I ran for 14 years using on 2 micron filters and a vacuum gauge, never had a clog and the gauge stayed in the green at all times.
That being said, I kept the fuel tank clean and filtered the diesel while fueling.
4-108.

Present boat has has a 300 hp Yanmar, now I go strictly with the makers recommended filters, 30 and 5, no problems either.

Not a stupid question, sometimes I have wondered which is the “Primary” filter and which is the “Secondary”.
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Old 01-01-2021, 10:22   #14
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Re: dumbest fuel filter question EVER.

My mechanic says that the filter on the engine is the Primary as it is the the primary, required source of fuel for the engine.

Racors and other external filters are secondary because they are optional and added to support/supplement the primary.

And thanks guys for the idea to use 2 micron on the Racors, makes a lot of sense!
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Old 01-01-2021, 10:44   #15
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Re: dumbest fuel filter question EVER.

I had so many fuel cleanliness issues, I installed Racor on my yanmar, an inline manual pump for priming the system plus the primary engine mounted filter.

I use 2 micron on the engine mount filter and 10 micron in the Racor.

If you plan to do much maintenance on your boat, I found this app is great for getting the correct manuals and specs.

ManualsLib. Go out to Google play or Apple store and download
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