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10 Micron or 30 Micron Fuel Filter?

Jun 5, 2014
209
Capital Yacths Newport MKIII 30 Punta Gorda, Fl
I'm still a newbie. The boat we bought back in April 2014 has a few extra parts. I was going to change the fuel filter and noticed that I have 2 extra fuel filters. One is 10 Micron and one is 30 microns.

I read about microns!
"A micron is a unit of measure equaling 1 millionth of a meter, or .000039 of an inch. The lower the micron rating, the finer the filtration. 2 micron filters more contaminants than 30 micron."

My 18HP Yanmar diesel engine currently has a 30 Micron fuel filter on it. So the previous owner left me a new 10 and 30 Micron fuel filter. So should I put the new 30 Micron on or is the 10 Micron better? Will the 10 Micron (finer filtration) mess up the fuel flow?

My engine also has a second fuel filter on it. It is a Puralator 50262.

See attached photos.

Thanks, Mike
 

Attachments

Aug 2, 2005
1,117
Pearson 33-2 & Typhoon 18 Penn Yan, NY (Seneca Lake SP)
I have considered the same question. Finer filtration at the Racor will trap most gunk brought out of the tank and into the fuel line. I was concerned that the 10 micron filter would clog up, but it would "save" the filter on the engine. The 30 micron would seem to share the filtering job more evenly between the two filters. A question to answer is: What is the micron size of the filter on the engine? A finer filter first seems incorrect in my mind. Also, is one filter more simple to change than the other? That might be a help in the decision. Let's both hope for a more definitive answer from other members!
Best Wishes
 

arf145

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Nov 4, 2010
429
Beneteau 331 Deale, MD
Where does the Purolator sit in the fuel flow order? Does your Yanmar have the standard secondary filter up on the front of the engine? That standard one is pretty fine--no use putting something too fine before that in the flow. I believe too fine a primary does make the lift pump work a little harder. I suspect either of the 10 or 30 is OK as a primary, but I wouldn't go for the 2 micron ones.
 
Jan 27, 2008
2,994
ODay 35 Beaufort, NC
RichH is the filter expert and should weigh in but there is tons of information on this if you search on the subject from previous threads. In short filters are not "absolute" meaning some particles larger than the filter rating are possible to pass. As the filter clogs up it restricts flow and will eventually starve your engine until it won't develop power and then stall. It is usually recommended to have a coarse filter first for your "primary" filter followed by the finer "secondary" filter on the motor. You should see what your engine recommends to help make your decision. A 10 micron is probably the lowest you should go for your "primary" filter. A micron is too small to see with the naked eye. A human hair is about .003 in diameter. A micron is almost 100 times smaller than that. 10 microns is .00039 or almost ten times smaller than a human hair diameter. The thickness of a sheet of paper is approximately .0015 so 10 microns is almost 4 times smaller than the thickness of a sheet of paper. Contaminants are not perfect little spheres they are all kinds of weird shapes so a 10 micron filter will capture some particles smaller and will pass some particles larger. I guess think of them like asteroids with all kinds of odd looking stuff. Plus you get gelatinous type stuff that might be soft and gooey. I use a 10 micron for my own primary filter but have a Universal (Kubota) motor.
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
The one nearest the fuel tank is the primary fuel filter and would be the 30mic filter. The filter on the engine would be the secondary filter and be the 10mic. filter. Decreasing filter mesh size as you near the engine.
 
Jun 5, 2014
209
Capital Yacths Newport MKIII 30 Punta Gorda, Fl
Both of my filters are easy to get too. The fuel runs through the Racor filter then through the fuel pump and then through the Puralator filter on the engine. I do not know what the Micron is on the puralator. The engine currently has a 30 micron filter on it.
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
30 will let alot of stuff go to the 10, and clog the 10, so put a ten in to be the first line of filtration- maybe even the second, as a 2 is too fine unless you have an electric pump pushing the fuel. This, from the Yanmar guy from Mack Boring.
 

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Yanmar specifies 15-18µM for that small engine mounted 'guard' filter. The Society of Automotive Engineers very long ago identified and specified 20µM as 'the most damaging' (hard) particle in a diesel engine.

Typical filtration for 98% of most diesel engines is: tank --> 30µM (optional prefilter) -->10µM (main or 'workhorse') filter --> 15-18µM (engine mounted 'guard' filter) --> engine. All these filters are at 95-97% removal efficiency at the µM rating - called 'nominal' rating.

It takes 'work' to accomplish filtration. Using a 2µM in place of a 10µM will: cause 1/5 to 1/10 the onstream filter life as in nature the smaller the particle the exponentially more of them ... a 2µM will block up and shut down flow about 10 times FASTER than a 10µM; 2µM will take 5X the pressure across the filter to make that filter deliver the exact same 'flow' and will/may cause premature failure of the engines lift pump diaphragm. If for some undefined reason you MUST use a 2µM instead of a 10µM you then should increase the surface area of that 2µM fllter (or use FIVE 2µM filters in a parallel arrangement and with all 2µM filters 'working') in place of that single 10µM.
Additionally, most particles in diesel fuel are soft and deformable; a 2µM filter will tend to 'extrude' these particles through a 2µM and since these soft/deformable particles do not 'burn' very well, will settle out in the exhaust system down stream of the combustion chambers and form thick 'coke' deposits on the walls of the exhaust system. Also too, a 2µM will also 'coalesce' particles much smaller than 2µM together, causing them to 'agglomerate' and grow into even larger particles downstream of that filter.
A few Ford and a few Volvo engines specify the usage of a 2µM.

30µM (optional) ---> 10µM --> 15-18µM engine 'guard' or 'last chance' filter.
The relative small surface area of that 15-18µM 'guard' filter will quickly plug and auto shut down the engine if any of the preceding filters break a pleat or start extruding a massive amount soft particles ... its really there only as a 'last chance' filter.

NO technically sound reason to use a 2µM filter on 98% of diesel engines.
 

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
30 will let alot of stuff go to the 10, and clog the 10, so put a ten in to be the first line of filtration- maybe even the second, as a 2 is too fine unless you have an electric pump pushing the fuel. This, from the Yanmar guy from Mack Boring.
Yes and no (the Mack Boring guy isnt telling the 'full story' ... and really shouldnt be saying such standing before 'recreational' boaters or 'consumers') .... the 30µM has a lot of capture sites in the filter material that are 10µM and smaller. The 30µM prefilters a quite high amount of 10µM particles from the oil thus extending the on stream service life of the 10µM. Use a 30µM to extend the on stream life of a 10µM ... based on historical need of premature failure/clogging of the 10µM - due to contaminated tank or contaminated fuel from unscrupulous or ill maintained supply sources.

He's only partly correct about the 2µM. Filters are selected/sized based on (gallons per hour per pounds per square inch differential pressure per effective filter surface area - Q/∆P). A vacuum driven system will 'stall' and stop pumping at about (negative) 6-7 inches of (hg.) vacuum, thats the 'best' vacuum you can get out of a single stage lift pump when its 'pulling' fuel ... greater than that 6" hg. vacuum the lift pump will stall and flow will stop, physically cant deliver more than 6-7inches of vacuum ...about -3psi negative pressure. An electric pump installed to 'push' the oil (pressure mode) can easily deliver upwards of 30 psi; and, if using the same sized filters will filter about 10 to 20 times the total amount of fuel ('throughput') as when in 'vacuum mode'.
Recreational boats have vacuum motive fuel supply simply because if there is a leak, air enters the system and quickly shuts down the engine ... and NO oil gets into the bilge to possibly cause a 'massive oil spill' onto the water. With a pressure fed system, the system has to be more robustly constructed (bombproof), with more expensive components (imagine the cost of 'banjo fittings' and seamless double flared tubing all the way from the tank to the engine!); and with 'pressure sensing instruments' to monitor for leaks ... OR alternatively must have a USCG certified 'engineer' onboard to constantly monitor the fuel system/engine. If you have a pressure feed system and it starts to leak, youre definitely going to fill the bilge, etc. with fuel oil.
 
Dec 25, 2000
4,981
Hunter Passage 42 Shelter Bay, WA
Fuel Filters

Hi Mike, it seems we have room for one more opinion.

Our 1991 P42 that we purchased in 2002 came equipped with a Yanmar 4JH2-TE tractor diesel and an Onan Cummins (Kubota three cylinder tractor diesel) 8KW Genset. Both have been very good performers over the years. Each engine has its own fuel filter; a spin on canister on the Yanmar and a cartridge filter on the Onan.

The PO had installed an after market unfamiliar brand fuel filter on the Yanmar and the Onan OEM was a two micron cartridge original equipment. Rather than purchase OEM spares I opted for NAPA brand spin on canisters as an alternative. Hunter installed Racor ten micron cartridge filters for both engines between the fuel tank and engine filter.

Professional transportation industrial diesel mechanics advised me that six micron fuel filters would be more than adequate contamination protection for our diesel engines. (RichH disputes their opinion) NAPA brand fuel filter part numbers of both engines follows:

Yanmar: NAPA 3390 ten micron canister filter.
Onan: NAPA 3426 six micron canister filter.
Racor: OEM 110 ten micron cartridge filter.

The Yanmar currently has 1,700 hours and Onan 450 hours.
 
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RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Terry, not to prolong the argument but Professional transportation diesel mechanics employers used to pay me an obscene lot of money to tell their mechanics exactly what filtration to use on their equipment. :)

The argument here is based on the totally arbitrary ratings that filter manufacturers apply to their products, so called 'nominal' ratings and which using the same exact filter media from the same exact filter builder and yet the distributors, etc. assign differing 'nominal'/arbitrary µM retention ratings.
The NAPA 3395 is built (most probably by Wix Filters of Gastonia, SC) to a FORD spec., one of the very few engine builders who specify 6µM (95% eff.). A Yanmar is not a Ford and Yanmar continues with the standard 20µM spec. thus youll find that that engine mounted 'guard' filter for 99% of common Yanmars is between 15 and 18µM (97% 'nominal') rating and the RACOR tech manual will insist that the 15-18µM guard (or last chance) filter is to be preceded by a standard RACOR 10µM (nominal).

;-)
 
Oct 9, 2008
1,724
Bristol 29.9 Dana Point
I'm glad someone brought this up. I've previously made assumptions based on history of the boat.

I have a universal m18 2 cyl 14 hp. Racor primary has a 2 mic. Elec pump behind it then to the engine which has a 2 mic spin on.

When I replaced the filters the spin on was immaculate inside after about 50 hours run time over 2+ years. I had expected as much given the primary rating, and wondered if I should change the primary to a 10. I replaced with a 2 mic again, and keep a 30 on hand in case it clogs.

So very little fuels flows. Maybe burns a gallon every 3 hours. And elec pressure in front of the injector pump.
Is this filter wrong? Motor runs fabulous.
 

RichH

.
Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Skipper - your Univ. M18 spec. if for a 18µM (nominal) filter.
If your history of long term operation shows virtually no clogging, your fuel from its supply source is CLEAN (see 'water glass test' in an above post) ... then the 2µM will be adequate.

Best is to apply a vacuum gage on the RACOR (to monitor the filter loading, so that youre not inadvertently 'surprised' ... plus with a vac gauge youll know if or when a pleat has broken in the filter that its on, and also know WHEN or if you need to change a filter.

Your engine spec. is for 18µM for the engine mounted filter. Still Id use a 10µM RACOR 'in front' or 'upstream' of it, simply because of its large 'surface area' and relatively slow liquid velocity through it.

;-)
 
Mar 19, 2010
30
Hunter 1997 376 Ventura, CA
Remember it does not take much to clog a fuel injector the better filter the more insurance you have for a good running engine. You may have to change the filter more often but you will not have to pay for cleaning injectors. Good luck Gary
 
Nov 26, 2008
1,932
Endeavour 42 Cruisin
Well, I'm running a spin on wix secondary of unknown size and a racor 10m primary. We put a lot of hours on our perkins 4.154 and knock on teak, no issues with fuel. And we buy fuel from a lot of different sources. I always try to find the cheapest source for diesel. The savings might only be $5 but I also know they are pumping a lot of fuel so it should be relatively fresh. Local sportfishers are pretty careful about not buying bad fuel.

BUT...I also have a polisher with a 10m racor and run it very frequently.
 

ALNims

.
Jul 31, 2014
208
Hunter 356 Huis Ten Bosch Marina, Sasebo, Japan
Both of my filters are easy to get too. The fuel runs through the Racor filter then through the fuel pump and then through the Puralator filter on the engine. I do not know what the Micron is on the puralator. The engine currently has a 30 micron filter on it.
The primary 30 micron is to filter fuel to the pump. The secondary filter on the pump discharge is to prevent particles from the pump from entering into the fuel system. If you put too small a micron filter on the pump suction side you can starve the pump and increase pump wear. The fuel going through the pump both cools and lubricates the pump. Your best bet is to consult the engine manufacturer and follow their recommendation.
 
Oct 9, 2008
1,724
Bristol 29.9 Dana Point
Skipper - your Univ. M18 spec. if for a 18µM (nominal) filter. If your history of long term operation shows virtually no clogging, your fuel from its supply source is CLEAN (see 'water glass test' in an above post) ... then the 2µM will be adequate. Best is to apply a vacuum gage on the RACOR (to monitor the filter loading, so that youre not inadvertently 'surprised' ... plus with a vac gauge youll know if or when a pleat has broken in the filter that its on, and also know WHEN or if you need to change a filter. Your engine spec. is for 18µM for the engine mounted filter. Still Id use a 10µM RACOR 'in front' or 'upstream' of it, simply because of its large 'surface area' and relatively slow liquid velocity through it. ;-)
Thanks Rich.
So would the vacuum gauge be installed between the Racor and the electric pump? - the pump is after the Racor on my setup- And is there a preferred gauge mfg?
Thanks again
 
Jan 27, 2008
2,994
ODay 35 Beaufort, NC
Racor sells a gauge that screws right into the top of the 500MA or similar filters. For the smaller filters you'd likely have to plumb it into the fuel line and mount it somehow. A simple T-fitting should do the trick for the plumbing.
 

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
What Jibes said, :)

For engines with mechanical lift pumps, the vac gage can go anywhere between the suction side of the lift pump and the filter you are monitoring. On standard RACOR filters (not engine mounted 'guard' filters) the gage would be mounted to the small outlet 'gage tap' or 'bleed tap' on the outlet side of the filter housing/head.
Note - Its best to isolate any gage with a small 'cock valve' and only have the gage 'on' when taking your readings. Gage --> cock valve --> fuel system (gage port on filter housing or 'tee' in the fuel line.)

The 'small' engine mounted filters supplied by the engine manufacturer are not usually designed for 'gross' particulate removal. Theyre there primarily as a 'last chance' filter ... in case the 'upstream' filtration breaches or has a 'break-through'. That 'upstream' filtration used to 'protect' the 'guard' is usually/typically RACOR type filtration @ 30µM (optional) --> 10µM.

Further, the engine mounted filter is usually located between the engine's lift pump and the high pressure injector pump .... and is therefore pressurized. If the 'guard' filter is actually being used as a 'guard' or 'last chance' filter, there is no need to put a gage on them - as usually either they either work or they almost instantly shut down the fuel supply to the engine if there is a 'breakthrough' from an upstream filter ..... no need for a (pressure) gage on the 'guard' filter.
Because of the relatively small surface area of the 'guard' filter; when an upstream 'breach' or 'filter breakthrough' occurs and even if the µM rating of the 'guard' is much larger than the µM rating of the filter that precedes it, - the relatively much higher fuel velocity in the 'guard' - even with much smaller particles than the filters rating - will 'bridge' across the larger 'pores', rapidly plug the 'guard' and quickly shut down the engine. A 'guard' filter either 'works' or or it rapidly plugs ... no gage required.

For the typical recreational boat filter set up:
30µM Racor type 'prefilter' (optional) --- vac gage on the outlet of the filter.
10µM Racor type 'main' filter --- vac. gage on the outlet of the filter.
15-18µM engine mounted 'guard'/last chance filter --- no gage required.

Typical set up: tank --> 30µM (optional) --> 10µM --> lift pump --> 15-18µM engine mounted 'guard' filter --> engine

How to use a vacuum gage to monitor filter condition:
•Initial data set-up with new/clean filters installed.
1. run engine at slightly higher than normal cruising rpm with prop turning (boat tied to a dock, etc.)
2. Very s-l-o-w-l-y close the tank valve until the engine just 'begins' to stumble (begins to lose rpm) - QUICKLY read the vac gage and then quickly OPEN the tank valve. This is the vacuum reading that will correlate to a 'fuel shut down' (insufficient fuel being delivered to) of the engine.
3. Multiply that gage reading value by 0.8
this 'corrected' vacuum reading is your - "change-the-filter(s)-as-soon-as-possible" value; but, you do have 20% 'reserve' left in that filter to get 'home'. All based on the vacuum developed in the fuel system while you are at 'cruising rpm' and the filters are new/clean.
•Normal operational monitoring:
4. Obviously you have to inspect (and record) the vacuum gage(s) occasionally while at cruising rpm to establish the profile of the filter loading to 'plugging'.
Some will apply an electronic (oil proof) vac gage with an integral 12vdc solenoid switch and adjustable 'set point' (that 'stumble' value 'times' 0.8) to trigger an alarm at a remote location - not cheap!
 
Sep 23, 2009
1,450
O'Day 34-At Last Rock Hall, Md
The primary 30 micron is to filter fuel to the pump. The secondary filter on the pump discharge is to prevent particles from the pump from entering into the fuel system. If you put too small a micron filter on the pump suction side you can starve the pump and increase pump wear. The fuel going through the pump both cools and lubricates the pump. Your best bet is to consult the engine manufacturer and follow their recommendation.
A very good point that I have never read or thought of. Also another reason why I follow RichH's advice and use a 30 um as my primary filter. Thank you both.
Although after doing so, I found, on page 7 of my m-25xpb manual "Install...filter/water separator between the fuel tank and the engine. Raycor 500 MAM (micron rated filter #2 or #10) is a good example of such a filter." The installation manual doesn't seem to cover the topic. It makes more sense to have the larger filter first.