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post #1 of 6 Old 01-19-2011 Thread Starter
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Old Diesel Fuel

I have just purchased a 1985 S2 9.2C with a Yanmar diesel. The boat hasn't been used in 2 years. The Yanmar turns over by hand just fine, and the oil looks fairly clean.


I'm hoping to get some advice on precautionary steps to take before I attempt to start the engine.

My main concern is the old diesel fuel in the tank. It is 1/4 full of old diesel fuel. Is there some magic additive out there that I can put in, top of the tank, and not have to worry about the age of the fuel?

Or do I need to drain and clean the tank- something I have no idea how to do.

I've looked in to fuel polishing services, and from what I have found, reviews are mixed at best.

I'm planning on changing the impeller on the raw water cooling pump before I try to start the engine.

What else am I missing? Any advice would be greatly appreciated. Thanks!
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post #2 of 6 Old 01-19-2011
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You really should get rid of that fuel...and probably give that tank a good cleaning if it has an inspection/cleaning port. If not, now might be a good time to invest in that. I'm not a huge fan of fuel polishing services as they really dont clean whats clinging to the sides of the tank unless the inject fluid at high velocity and pressure to clean out the scale buildup.

Besides, you could build your own fuel polishing rig for about $300 which is less than the cost of the services, I'll bet, and you'll have a system to clean fuel from here on out. eBay for a Racor 500, a walbor fuel pump, some fittings and some lines and you can rig this up yourself. If you want to mount it permanently on the boat, then the cost may be a bit more.

Howver, its not worth the $50-$100 you'd save by using the old fuel...

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post #3 of 6 Old 01-19-2011
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A quarter of a tank is what, 8 or 10 gallons? Get rid of it. Take it to you local haz-mat collection point if you have to, along with all the crud you get out of the bottom of the tank when you clean it (and the solvent and rags you use). While you're at it, replace all the fuel hoses if they don't look brand new, and replace your fuel filter(s).
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post #4 of 6 Old 01-20-2011
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Despite what the oil looks like, it will need to be changed. The oil will break down over months, let alone years. Consider changing all filters as well.

Not that I would really want to see anyone burn that fuel, but there will undoubtedly be someone willing to take it and use it, if you ask around. Tell them they can have it for the price of getting it off your boat.
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post #5 of 6 Old 01-20-2011
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The best course is to siphon from the very bottom of the tank to be sure there is not a LOT of free water that has settled-out from the oil. Free water ('slugs') that comes in contact with hot injectors can/will destroy them.

Second, withdraw a sample of oil, put it into a clear glass container and hold it between strong light and your eyeball. If there is any notable 'haze' in the fuel, get rid of it.
If there is a noted 'discoloration' (not clear or clear-red; but is 'black-ish' or 'dark'), get rid of it and clean out your tank ... either by opening the tank and mechanically scrubbing the tank internals (best method); or, if the tank has no access ports by use of a chemical tank cleaner such as Starbrite "Tank Cleaner", etc.. If the tank has access ports, simply FEEL the internal walls for 'growth' accumulations on the walls; and if so, definitely clean the tank.

Recirculation polishing of the oil without a thorough tank cleaning is of absolutely NO benefit.

If all the oil-gods have aligned well - - - - no haze, no water (or you can remove the water), no 'discolored' oil ... then you're probably 'good to go' ... but still use a chemical tank cleaner to be sure. It all depends on how fouled this tank has become over time.
'Infected' tanks will require significant cleaning, etc. and yet others will retain good quality oil for very long intervals .... all depends on the oil-gods, the 'hygiene' of the tank, and the roll of the dice.

Rx: Sample the oil for haze/discoloration, check for free water, clean the tank if necessary.
Note: If there 'is' free water, absolutely change ALL the filters, including the engine mounted 'guard filter' - water over time will 'digest' and soften the cellulose fibers in fuel filters.

Small volumes of contaminated oil usually can be safely burned in a home oil burner, if all the visible water can be removed. Add a bit of 'chemical tank cleaner' to the contaminated oil and let 'sit' for several weeks or more before you add it to a home oil burner tank.

hope this helps
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post #6 of 6 Old 01-23-2011
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Diesel fuel will be good for several years. What kind of filter do you have? Does it have a clear inspection bowl? Does it look dirty and/or can you see water in the bowl.? Do you have a secondary filter?

I'd start the engine and let it run in gear for a while with engine rpms about 2000—20 or thirty minutes. If it stops on its own, check to see if there is water or air in the filter. If it runs OK for that long, let it run for another half hour you probably have no problem. Filters will filter out all the algae, etc., before it gets to your injectors. Your big problems will probably be water or air in the system.

If the engine stops, check the primary filter to see if you have water or air in the system. Close the tank valve and replace the primary and secondary filters. Drain the water from the bottom of the primary filter, top the filter off with fuel. Then open the tank valve and use the fuel lift pump to bleed the secondary filter until all the air bubbles stop completely. Do the same for the injector pump. Then try to start it again. Repeat the above bleeding process until it runs smoothly.

Most diesel tanks have a certain amount of water or algae in the bottom. Do you have an inpection port to look into your tank? Or can you get an arm in the tank to clean it? Probably not. But that's what filters are for. You could pump the water out of the tank—it will be on the bottom of the tank as it is heavier than diesel. Use Biobor or similar biocide to kill the algae—your filter will strain out whatever comes through.

Bottom line—always check your primary filter—Racor with clear plastic bottom is best, replace filters when dirty, and know how to bleed your system. Good luck

Last edited by olgriz; 01-23-2011 at 11:21 PM. Reason: additional info
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