Gravity Running Tank for Engine

[capecodphyllis]

Any comments as to the feasibility of using a dedicated, gravity fed, diesel fuel running tank, mounted in the engine compartment?

Other than limiting range, or needing to keep refilling it, what's the down side?

Supposedly, this would make it easier to keep water and muck from finding it's way from the main tanks into the engine.

Thoughts?

[camaraderie]

Its' a good idea if you have the space and the ability to run the lines. A lot of larger boats use this system with lift pumps and filters in line from a couple of other tanks. The only downside is that if you forget to top up the "day" tank...you end up sucking air into your diesel which is never any fun!

[sailingdog]

You'd also have to run the diesel return lines up to the tank or it will run out very quickly...

It might be a better investment to install a proper fuel filtering setup on your main tank... rather than trying to jury rig a day-tank.

Consider this: what if you're powering in a storm, and the day-tank runs out as you approach a lee shore...would you be able to fill the tank in those conditions... would you want to try???

[jones2r]

The day tank concept has never made much sense to me. It anticipates maintenance problems that may be better addressed through good maintenance procedure, i.e., replace old pumps before they fail, etc. The day tank adds complexity to a system in which simplicity is a virtue.

I am interested in a method for preventing the contaminated fuel problem. Aside from the Baja filter, I am interested in assembling a filter/separator that would be used during the fueling process. That way you don't carry impending maintenance problems in the fuel tank that would have to be coped with by the on-board filter/separator system. Does anyone have thoughts on the practicality/design of such a rig?

[sailingdog]

jones2r-

You could always install and on-board fuel polishing system... that would get rid of the sediment, water and sludge that cause 99% of all diesel fuel system problems. If you design it to run off an electric fuel pump, with proper filters, then run it when you're motoring, it would help prevent a lot of the problems that most boats run into.

Proper maintenance of the fuel tanks and such is also a necessity.

[georgellop]

The "day tank" concept is only useful when you have more than one tank i.e. all the tanks except the day tank are storage tanks. Usually the day tank is sized to last 24 hrs running (day) and only fuel which has been filtered by an onboard system is put into the day tank.

If you only have one tank then you can install a "polishing" system which circulates fuel on a timer. You can polish while you "run" or at the dock. Most day tank installations have the option to polish the fuel while running even though the fuel in the day tank has already been polished less than 24 hrs ago. Make sure that you use filters meant to go on the vacuum side of the system; or, if using filters on the pressure side make sure you install a bypass.

I believe that cruising sailboats would benefit greatly from an onboard polishing system. After all contaminated fuel is our biggest concern whether the contamination originates at the pump or in our own tanks.

Regards,

[RichH]

You can arrange a day tank so that its always filled by the main system with already filtered fuel, etc. Such an arangement is constructed so that the tank never empties as the exit nozzle is higher than the fill nozzle and is always filled but when your lift pump fails or you filters 'choke' .... just manually throw a **** to allow the tank to vent to atmosphere and throw another one to drain the day tank directly into the remaining system. On most 30-40 ft. boats a 3 gallon day tank will allow about 4 hours of operation (at .75 GPM flow. :-)

My personal fuel system is somewhat complicated but simple in concept: recirculation Fuel polishing system is on whenever engine is on ---> Single but LARGE Racor in main delivery piping ---> day tank (locked out until 'needed' but always storing ~3 gallon of clean filtered oil) mounted ABOVE engine so it can gravity feed --->'choke filter on engine, etc. System is pressure feed so all the filters are at better removal efficiency and on-stream service life (electric pump is at the main TANK). Polishing system maintains tank at less than submicronic levels using 5uM depth type filter. Tank is manually cleaned every 2 years. All lines are stainless steel with double flared connections ... as copper is reactive with diesel fuel. I change the Racor about every 3-5 years (based on operating pressure differential vs. engine max rpm) as all the filtration 'work' is accomplished by the polisher leaving the Racor as a 'redundant' or last chance filter ... I track the DP gage to monitor system performance and alway KNOW long before I NEED to change a Racor. My typical resident particle distribution in the tank from constant recirculation through 5uM on board polishing filters is essentially sub-micronic (based on nephalometry (light scattering) coorelation measurements ... ie.: the oil is always CRYSTAL clear.

I visually inspect all fuel before taking it onboard ... if its not 'fresh' or has visual haze when held to bright white light in clear glass container ... I simply go somewhere else. I usually get my fuel from a truck stop and carry it in or only buy from fuel depots that service the commercial marine trade. I put onboard only what I plan to use plus a bit for reserve. I never FILL the tank and use a desiccant vapor absorbing filter on the tank vent .... no water vapor intrusion (water vapor/humidity equilibration). When off the boat for long term I close the tank vent valve (my tank is rated for high vacuum and some pressure) ... I built the tank.

I find that almost all diesel fuel systems on 'boats' are poorly designed (vacuum feed ... which is bad as a filtration application and BAD from a hydrodynamic viewpoint as vacuum motive systems - suck), contain a lot of copper (reactive with #2 fuel) .... and are built that way because thats the absolute cheapest way to do it (cheap and dirty).

I (hope) dont worry about tank slime, bacterial debris from breaking loose from the tank walls in a heavy seaway .... If it does, I always have 4 hours of CLEAN fuel in the daytank ... and dont have to risk power-puking into the bilge because of plugged filters. If all hell breaks loose (broken lift pump, 'particulating' tank, etc. ... , I can wait 3-4 hours before I HAVE to do 'something'. :-)

[capecodphyllis]

Originally Posted by RichH

You can arrange a day tank so that its always filled by the main system with already filtered fuel, etc. ...... :-)

Holy sh**. You've really covered all of the bases!

My thoughts were to have a gravity 'day' tank which I would fill with 'already filtered and treated' fuel kept stored in a couple of jerricans. I would simply pour it in.

I'm just thinking out loud here. Trying to imagine the simplest bulletproof system.

What are your thoughts about fuel Additives to increase cetane ratings and lubricity? (Sometimes I wonder if that stuff is just for suckers.)

[capecodphyllis]

Originally Posted by sailingdog

...what if you're powering in a storm, and the day-tank runs out as you approach a lee shore...would you be able to fill the tank in those conditions... would you want to try???

What happens if I go cruising on a sailboat without any engine at all? I do it every summer.

To a person used to sailing without an engine, a step up to an engine with a 'day tank' would be a real luxury.

[RichH]

I run an ancient old Yanmar 3Qm30 and the fuel nowadays is nowhere near the specs. of 20-30 years ago. Definitely I use a cetane booster, (and I used to use a re-lead compound in my Atomic-4, etc. )