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I've recently purchased an old Westerly Nomad, and although engine has been working fine, I only ran it for about 10 hrs end of last year and I want to change both Primary and secondary fuel filters so that I know they have both been done.

Which one should I change first ?

I have never done this before, but think I understand the basics from watching youtube video's.

But my thinking is when I replace them I will possibly be disturbing sediment on the existing filters that might have built up.

Would it be best to replace the primary filter first, although this might be the dirtiest, and more chance to disturb sediment, it would be caught by the 2ndary.

get the engine started and run for 5-10 mins.

Then replace the 2ndary -> prime and restart.

Or would it be better to reverse the procedure, under the assumption that the 2ndary is the cleanest and least likely to disturb build up, then move onto the primary?
 

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If you have two filters then the first one is an aftermarket one. many only use the stock Yanmar engine filter. with an after market filter in place the second filter is really not doing much at all. with the flow of a 1GM10 doubt you will even have anything in the second filter. I have stock and after market Racor on my 1GM10 and change both at the same time never have had a problem.
 

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Overboard is right. First filter is aftermarket. Second is your yanmar. Your overthinking this. Just replace both. Then prime your fuel system. Little pump, you'll find it if you trace your fuel lines. And your good to go. You can fill the canister with ATF fluid to help with priming.
 

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Be careful with the primary, it's really easy to get the o-ring caught up, and don't go mad on the bleed screw. Both will result in leaks.
 

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It doesn't matter which filter is changed first as the bulk of the captured debris will be 'within' and held fast by the filter material. Any minuscule amount of debris not cleaned from the 'sump' of the filter will be captured by that reinstalled/new filter during re-start.

Typically and functionally the engine mounted 'guard' or 'last chance' filter has the most convenient air bleed - for purging air; so, the 'guard' filter is the easiest to bleed air. You can most conveniently air bleed both filters through the air bleed on the engine mounted 'guard' filter.
Change the pre filter(s) and the engine mounted guard filter; purge the air through whatever pre-filter is installed and continue to purge the air through the engine guard filter. Doing the air purge separately will only waste time, and oil. Do it all the air bleeding at the same time.

Note: Be careful in cross matching the µM retention rating to be consistent with the engine manufacturers specification ... for example: the small 'guard' filter on Yanmars is typically specified @ 15 to 17 µM. The typical correct pre-filter to the 15 to 17µM engine mounted 'guard' filter (again, for Yanmars) will be a 10µM 'prefilter'.... and is of smaller retention µM rating than the the 'final' or 'guard' filter. Such filters are NOT 100% removal efficient at their 'rating' so don't be alarmed at the smaller retention in place before the final/guard/last-chance filter. Volvo marine engines usually will have 'finer' filter µM requirements.
Lastly, DO NOT substitute a smaller µM retention filter than that specified by the engine manufacturer.

Typical set up for Yanmars: tank --> 1st pre-filter (optional) @ 30µM --> pre-filter 10µM --> engine guard filter 15-17µM --> engine.
 

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Yanmar OEM primary is 10-15 micron, I have a 2 micron before that. Make sure to pre-fill the secondary (the bigger) filter with fuel, saves you a lot of time poking the little fuel pump lever. First bleed to the point on top of the primary, then the injection pump. You hopefully won't need to do the high-pressure side, run the engine for a good 15 minutes, if it runs then the high-pressure side is fine. If it dies, you likely need to have another go at bleeding the system (took me a couple of tries my first time), including the high pressure (crack open the fuel pipe to the injector and turn the engine over, then close it up once the bubbling stops).
Have fun :)
 

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FWIW .....
filters are 'sized' with respect to µM 'rating' based on flow capacity - gallons per minute per square ft. of surface area per pressure drop across the filter.

A 2µM has a very 'tight' pore structure
A 10µM has a quite 'open' pore structure.
A 2µM has 1/5th the flow capacity of a 10µM ...... to deliver the same amount of fuel the 2µM must be operating at 5 TIMES the pressure drop across the filter than a 10µM. Or if operating at the same pressure drop, a 2µM will deliver only 1/5 the amount of fuel as a 10µM.

This means that a 2µM in a fuel system that was designed / selected a 10µM (engine designed for 20µM 'most damaging particle')..... will be putting ONE HELL OF A LOAD onto the diaphragm of the lift pump - expect premature fuel pump failure. Worse, there are exponentially more particles at the 'smaller' size range than the spec'd. size .... the 2µM filter will choke with debris about 10 times 'faster' than a 10µM.
Even (more) worse, most of the debris in diesel fuel is mostly biological (fungal fragments, dead cells., etc.) which are deformable and which under increasing pressure across such a filter will begin to EXTRUDE right through the filter media ...... these 'deformable' do no burn well in the combustion chamber but probably are the chief source of 'coke' that blocks an exhaust system.
 

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Filter is rated at 30 gph so I'm not overly concerned about flow rate, could probably move to a 10micron. Fuel system itself is nice and clean.
 

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Rich,

Correct me if I am wrong here. One could put a 5x bigger filter in the 2um filter vs the 10um. Have the 2um be a 2 micron, and the 10um being say a 10 micron could they not?

As I recall, my 2gm is a 2micron, altho it may be the 2um at the engine, I've gone with a 10m racor before it. This seems to get most of the mess when the time comes.....I[ve been told not to use a smaller micron secondary vs the primary later in the line, so I have not done so. The racor is good to 8 or 15 gpm. If I do more than 1gpm I am at FULL throttle. Usually about .5-.9 gpm for most useage. I can not imagine a 1gm being any higher use gpm wise.

Marty
 

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I have mainly used a 2 micron in the Raycor and the suggested 10micron in the engine filter because a Yanmar dude told me to.
But now just as often I use 10micron in both.

In either case change both together otherwise you are just wasteing time.

On the point about running the engine after bleeding: I find 10 minutes without load bloody useless. I go for a lap around the park at normal revs for 20 minutes. Sometimes the last bubble are not out for 15 mins and it can be a bit of a worry if its gunna cut out.

As a general point from a guy who ain't no mechanic whatsoever...: Do not fear the engine! Just get in and change the filters, oil, etc when you need to. These engines are pretty good and they are pretty hard for an amateur with a brain to stuff up.

Swearing helps :)

After a couple of filter, oil changes etc, its all quite easy :)
 

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Rich,

Correct me if I am wrong here. One could put a 5x bigger filter in the 2um filter vs the 10um. Have the 2um be a 2 micron, and the 10um being say a 10 micron could they not?

As I recall, my 2gm is a 2micron, altho it may be the 2um at the engine, I've gone with a 10m racor before it. This seems to get most of the mess when the time comes.....I[ve been told not to use a smaller micron secondary vs the primary later in the line, so I have not done so. The racor is good to 8 or 15 gpm. If I do more than 1gpm I am at FULL throttle. Usually about .5-.9 gpm for most useage. I can not imagine a 1gm being any higher use gpm wise.

Marty
Spot on with the statement that if you for 'some' reason elect to change the normal 10µM, you should increase the surface area by about 5X. Sizing is based on maximum fuel consumption RATE .... Wide open throttle + about 25%.
However, since in nature always there are exponentially more smaller particles than larger particles you risk having to perform rapid and serial changeout if the system becomes fouled or contaminated - especially if the filter system is 'undersized'. Golden rule for filter selection if you deem the filtration to be 'critical': oversize, oversize the filter SURFACE AREA.

2µM filtration was never specified by Yanmar in the QM nor GM engines ..... their spec if for a 15 to 17 µM FILTER... or 'slightly smaller' than the 20µM, defined as the most damaging particle size in a diesel engines fuel system.

The engine manufacturers filter recommendations are based on the assumption of normally clean fuel or very slightly contaminated fuel. When there is an upset due to contaminated fuel and that upset has become regularly occurring (you usually buy your fuel from the stagnant tanks with old fuel from your local marina OR your tank is grossly contaminated with fungus and/or bacteria), then the first consideration is to add additional pre-filters and also to increase the existing filters SURFACE AREA.

Normal for Yanmar QM & GM engines:.
tank --> 10µM (Racor) --> 15-17µM (guard) --> engine

If frequently contaminated fuel (and you've cleaned your tank) b use your supply source is 'dirty':
tank --> 30µM Racor --> 10µM Racor --> 15-17µM guard filter --> engine.

The 'best' is to do all 'coarse' filtration independently from the fuel delivery system - a recirculation system from the tank, filter, back to the tank ..... essentially no particles go to the engine guard filter. About $300 for a DIY installation; Racor/Parker now offers onboard recirculation filtration 'packages'.

Lastly, any filter 'set' should be monitored with (vacuum) gages, so you know WHEN to change out the filters. Can be gages with electronic set-points wired to an alarm circuit; the 'set' vacuum (pressure) at about 80-90% of the developed vacuum when the engine is running at FULL BLAST and under full load - wide open throttle. Better to know (the alarm sounding) you have an hour or extra run time before you need to change the filters while underway, than have to do so because you're surprised that you're dead in the water, etc. etc.

hope this helps.
 

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Discussion Starter #12
I'd Just like to thank everybody for their encouragement and help on this topic. I've purchased a Yanmar filter for the engine, and CAV for the pre/after-market filter. I'll take images and send feedback in case it helps others tackling this task in the future. Boat is on a mud berth, so I'll wait till boat next floats before starting. I guess I have been over-thinking the project.
 
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