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Old 03-18-2012
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rerouting fuel return away from tank

Was wondering if anyone has heard/thought about
rerouting fuel return away from tank to small aux tank/container. We are always looking to keep diesel fuel
and tanks as clean and minimize water so thinking that
not recycling hot nasty 1/2 spent diesel back to tank and mixing with clean cooler diesel may have some merit?
Not mixing hot returning diesel would cut down on
condensation which could lead to water, which could lead
to nasty growing things in tank....either not using in boat at all(preferred)...or not routing back to main tank until cooled off.
Not looking for more boat projects, but wondering?
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Old 03-19-2012
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Re: rerouting fuel return away from tank

I'd be more worried about forgetting about that 'small' tank and either dead ending the return or spilling fuel ...

The fuel returned is not '1/2 spent', it's simply recirculated back, and I wonder just how much 'hotter' it really is.. some, I guess, but I'm not thinking it's a big source of troubles since every boat does it this way.

I wouldn't try to reinvent the wheel and just keep your tank on the full side to avoid condensation as much as possible. The last thing you want to do is mess with a fuel system that's working well...
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Old 03-19-2012
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Re: rerouting fuel return away from tank

The return fuel is cleaner then when you bought it as it was pumped through the fuel filter. this helps keep the fuel in the tank polished. the clean return fuel is not 1/2 spent it is just excess fuel that was bypassed by the fuel injector. Another Old sailor's wives tail
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Old 03-19-2012
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Re: rerouting fuel return away from tank

Thanks Faster and overbored, all good points. What brought subject to front was...
all set up for day tank which have used over years off and on, and now will discontinue.
Will continue to keep tank on full side and clean every few years.
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Old 03-19-2012
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Re: rerouting fuel return away from tank

You can certainly fill a day tank for a stove, etc with the return or direct it to a different tank for balancing, or as part of a polishing plan (as Faster said you need to monitor it closely). As stated above there is no degradation of the returned fuel.
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Old 03-19-2012
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Re: rerouting fuel return away from tank

On the wet coast we're glad to have a dickenson oil stove.I've done both pulse pump and gravity feed. On Thane I installed a day tank(about3 gal) It's filled by return from injectors or a pulse pump on a timer from an old kitchen appliance .It vents to outside on the coaming and the main tanks vent to day tank(and take it's overflow) Big vents on the deck fills(when open) allow faster filling of the 650 liters it takes to fill. The day tank has a sump drain to catch the condensation as it occurs so it's a small problem for the main tanks.I can also direct the day tank into fuel manifold (remember to shut off the surprisingly empty main tank before opening the emergency fuel supply) Good for failed primary fuel pump or bleeding filters too. It may sound complicated but a bit of planning and good labeling always helps

Last edited by Capt Len; 03-19-2012 at 07:21 PM.
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Re: rerouting fuel return away from tank

Recently someone described how he just used his alternate, secondary fuel filter as a polishing filter. That is he used one of those small electric fuel pumps to pump fuel thru the spare filter whenever the engine was on. So this kept the tank clean I suppose also helped take out water that's above the suction. Sounds like a good idea.
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Old 03-20-2012
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Re: rerouting fuel return away from tank

Quote:
Originally Posted by HUGOSALT View Post
Was wondering if anyone has heard/thought about
rerouting fuel return away from tank to small aux tank/container. We are always looking to keep diesel fuel
and tanks as clean and minimize water so thinking that
not recycling hot nasty 1/2 spent diesel back to tank and mixing with clean cooler diesel may have some merit?
Not mixing hot returning diesel would cut down on
condensation which could lead to water, which could lead
to nasty growing things in tank....either not using in boat at all(preferred)...or not routing back to main tank until cooled off.
Not looking for more boat projects, but wondering?
Here is why that would be a bad idea.

Fuel must re circulate to keep the fuel flowing and filtered.
It also raises the fuel temp to allow it to burn cleaner.
As fuel temp rises the little critters that like to live in fuel die and are filtered out.
Fuel is not just fuel for a Diesel, is it lube,cleaner and a cooling system for fuel components.

If you are afraid of metal contamination in your fuel tank install a large low drag fuel filter on return side. 30-50 micron to stop anything from returning to tank.
Keep in mind that a plugging filter on return has the same effect as a plugging filter on supply side. so no fine micron filters.
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Old 03-20-2012
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Re: rerouting fuel return away from tank

That nasty "used" diesel isn't used at all, it has been filtered and cleaned and simply bypassed the injectors. And because it is hot, it will keep the fuel tank warm(er) and may actually help discourage condenstation that a cold tank would suffer. Condensation forms on cold surfaces, not hot ones.

Yes, warmer diesel may foster more growth, but I doubt the returned diesel is going to make any real difference that way. It is simply CLEANER than what is in your tank, because it has already been filtered.

Not worth worrying about.
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Re: rerouting fuel return away from tank

Thanks guys as always (well usually) knowledgeable well thought out responses. Return will stay right where it is.
Little background ...number of years ago had air leak somewhere in fuel line and/or filters...symptoms were motor would run all day if
motoring or not healing much...but as soon as boat heeled more than say 10-12 degrees (port or starboard tac) motor would start at end of sail...run for 8-10 minutes and then quit. After bleeding from secondary filter to injectors, would start up again and run just fine. (I learned how to bleed line real well in all conditions) It was during that time I installed day tank and developed keen interest in fuel and it's delivery. I and some very confident accomplished mechanics never found speciific problem, but over a 2 years changed enough on fuel system to fix! Lot of memories though,
including motoring home with fuel line connected directly to 2 liter soda bottle with bottom cut out, duct taped to rail upside down, just had to keep refilling before got to low!
Thanks again, Hugo
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