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z1nonlyone 03-22-2004 05:18 AM

Diesel Blues
I am experiancing some troubles with my 23 year old Yanmar 2 cyl. diesel. During operation, the rpm''s occasionally fluctuate and drop then it resumes its correct rpm again. It does this for about 15 stressful minutes before again returning to its proper rpm. I think that maybe the fuel pickup is clogged or something. It seems to be definatly fuel related. I have clean filters (racor) on the fuel system. Is there a way to clean the tank and fuel?

WHOOSH 03-22-2004 05:37 AM

Diesel Blues

Yes, you can have the tank''s fuel cleaned (or ''polished'') but I don''t think that''s your problem.

Have you replaced the primary fuel filter (the one mounted on the engine, not the fuel filter/separator thru which the fuel first passes when leaving the tank)?

What age is your boat? Until the 90''s, many boats came with tanks built with the pick-up tube (which feeds your fuel line enroute your engine) with a mesh screen over the tube. Over many years, particles can easily fill this mesh screen (or nearly so) and either stop the engine totally or make the little diaphram fuel pump work oh-so-hard to get not quite enough fuel. You should be able remove the fuel line at the secondary fuel filter/water separator, slip on a dual barb fitting and a short piece of clean vinyl hose and then blow backwards into the tank, feeling steady backpressure due to the head pressure of the fuel in the tank. You should hear it gurgling. (You did check your fuel shut off valve to make sure it''s open all the way, right?) If you can''t do that, it''s time to get out the dinghy pump, build up an adapter that allows you to connect the pump hose to the fuel line, and then push via air the crud off/out of the mesh screen in the tank. (You may also be able to pull the pick-up tube to check it, but often this isn''t possible without first removing the tank).

I once had to construct a completely new fuel supply from an old tank to my Racors when the tank''s pick-up tube screen filled up; it was offshore at night and it wasn''t fun. I didn''t think of the dinghy pump idea until after I''d confirmed it was the pick-up tube that was the problem...wished I''d thought of that earlier in the process!

Let us know how it goes, and hopefully there''ll be other suggestions along with this one.


RichH 03-22-2004 06:10 AM

Diesel Blues
Symptoms are suggestive of an air leak in the fuel system piping. Boat fuel piping when ''compression'' fittings are applied are very subject to ingress of air; solution: (if thats the problem) is to install/replace with flared fittings. Older fuel oil filter sets used neoprene/BUNA rubber seals, modern filter sets now use EPDM (ethylenepropylenediaminemonomer) which dont ''age'' as badly as neoprene/BUNA. Carefully inspect the seals on the Racors, etc. for aging seals.

A visual inspection of the tank internals will quickly show if the need for cleaning is waranted. Cleaning is best performed by mechanical scrubbing the internals, followed by a high pressure wash with detergent, etc. If you have a thick ''black'' coating on the surface walls of the tankage that would indicated polymerization of old fuel, if ''slimey'' would indicate a bacterial infection. Actual cleaning is usually the best remedy. However, for future attenuation of ''particles'' you can apply an onboard recirculation/polishing system consisting of a dip tube to the very bottom of the tank, a 20ÁM ''depth'' filter, followed by a 12v transfer pump (wired to the engine panel) and a delivery tube back to the tank. The 15-20uM filter set is run any time the engine is on and will keep the resident particles to a ''sub-micronic'' level (due to % (wt.) removal of such particles at each ''pass''. For a bombproof system consider to apply an independent 2-3 gallon gravity feed ''day'' tank between the Racors and the engine ... so that if you have any ''problems'' you can switch to the day tank run for about 3 hours and ''sort the problem later. If you want the schematic of my system, email me direct. (I''m very deeply involved in filtration engineering.)

Sasha_V 03-22-2004 04:18 PM

Diesel Blues
I would certainly like a copy of that diagram, please.

thank you.


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