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Old 03-02-2019, 18:17   #1
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Diesel Fuel Tank

I have a 1978 Pearson 356 ketch rig sail number 233. We sail on a local bay and sail approximately 25 to 30 times a year. We have a 40 hp Westerbeke engine to get to open water to set sails. We use about 2 or 3 gallons of fuel a year. We keep about 5 gallons of diesel in the 40 gallon main tank. I would like to make a small removable 5 gallon fuel tank to use for local use and keep the 40 gallon tank for extended trips. The 5 gallon tank would be inline with the main tank with a series of valves to switch between the 5 gallon tank and the 40 gallon tank. By using the small tank the fuel would be fresh fuel and the 40 gallon tank would be empty and checked periodically for cleanliness. Has anyone use a system like described ? I would like any pros and cons. Any comments would be appreciated. Thanks.
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Old 03-02-2019, 19:01   #2
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Re: Diesel Fuel Tank

Empty, clean and cap (leave the vent) on the big tank, install the small one and route your fill and fuel lines (if you can use the existing ones and leave them full length) to the small tank. Donít bother installing transfer pumps, extra lines or anything else until you or the next owner decide itís required. Good idea for what youíre currently doing. It will be very simple to re-run the lines when you plan to do it. If at that point you want to run fuel from the main tank to the day tank, install the hose, pumps, filters and valves then.
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Old 03-02-2019, 19:57   #3
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Re: Diesel Fuel Tank

I don't see the need for the smaller tank. Just put 5 gal in the big tank, how is that different than 5 gal in a small tank?


If you are worried about the fuel sitting during the off season, just drain it.
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Old 20-04-2019, 01:04   #4
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Re: Diesel Fuel Tank

5 gallons swilling around in a 45-Gallon tank is very different. Just think of all the air youíll suck up in a rough sea. Use the day tank.
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Old 20-04-2019, 04:16   #5
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Re: Diesel Fuel Tank

FWIW I like the overall plan and RBK's suggestions. I might add considering putting one of the vent line filter systems inliine on the main tank's vent while the maIn is pickled to further help keep water etc out of the tank.
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Old 20-04-2019, 05:08   #6
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Diesel Fuel Tank

What is the large tank made of? It is likely to end up with a fair bit of condensation when empty and if steel, may rust. Either way, do you have a way of removing condensation from that tank if it forms?

As for the design idea, Iíd put the small and the large tanks in a Y configuration rather than in series. Then contamination of one tank can be managed by isolation.

For the record, I made my new day tank out of fibreglass when the original stainless day tank started to leak. Despite the dire predictions of a few I am still alive, years on.

I do like the idea of a smaller tank in conjunction with a main tank, but consider how you might easily refuel the small tank when under way as an unexpectedly long motoring session may leave you short of fuel and needing to resort to the jerry can of extra fuel you wisely stored on board for just this situation.
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Old 20-04-2019, 05:41   #7
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Re: Diesel Fuel Tank

I came across a suggestion elsewhere:

- locate a small (2-gallon) day tank above the engine, so that it gravity-feeds
- supply this tank from the secondary filter - the engine lift-pump is used to feed it.
- route the return line to the day tank
- install an overflow from the day tank back to the main tank.

That way, the day tank is always full, and small enough to be located so it is accessible. A sight-tube should be used to monitor it.

A low-level alarm on this tank, or better still an alarm on a filter pressure gauge, would give enough warning to go and replace a dying filter.

I liked this approach - I had a (large) day tank on my last boat (a power boat), and it gave me a huge amount of comfort, knowing that only crystal-clear juice was going to the engines.

Eamonn
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Old 24-04-2019, 12:18   #8
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Re: Diesel Fuel Tank

I have similar setting with the 20 Gallon diesel tank for 3GM (30HP) yanmar. Diesel fuel does not age if it is handled correctly.
First i never pump diesel direct to the tank. At the distributor I fill (2) 5 Gallon jugs with water/diesel separator funnel. I leave jugs to rest for at least overnight. Then I pump by siphon tube approx 4.5 gallon via fine mesh filter to the tank. The last 0.5 five gallon stays on the jug for next refill until the end of the season when it is discarded or used for cleaning tools. The jugs are cleaned yearly.
I try to keep the fuel tank full all the time to prevent condensation. Combined with dual Racor engine filters has always worked for me for last 15 years or so. I did clean the diesel tank once five years ago (after my 10 years of use) and found nothing but a thin dark film of condensation on the bottom.
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Old 24-04-2019, 20:00   #9
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Re: Diesel Fuel Tank

British Petroleum and others would disagree, they say Diesel does have a storage life
https://www.bp.com/content/dam/bp-co...age-diesel.pdf
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Old 24-04-2019, 21:37   #10
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Re: Diesel Fuel Tank

BP said that ULSD doesn't really have a shelf life if handled appropriately, from the reference (emphasis added):
"In underground storage low sulphur diesel fuel can be expected to last at least 5 years provided steps are taken to keep water and fungus out and potentially up to 10 years or more with regular inspection."

99.something% of the molecules that leave the refinery are tens of millions of years old. What's a few more years between friends. The problem is the types and rates of reactions possible in the new tank environment. The referenced .pdf basically says "keep all water and floaties away from the fuel, and metal too if possible"--all to reduce the types/rates of reactions in the new storage tank. Hard to keep oxygen out, so BP says to filter the gum regularly.

If one has an engine system that is tolerant of a small percent of hydrocarbon re-arrangement in the fuel (from oxidative processes secondary to exposure to air in the tank), then, practically speaking, diesel doesn't have a shelf life...assuming water and particulates are routinely removed from the fuel.
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Old 25-04-2019, 08:41   #11
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Re: Diesel Fuel Tank

ULSD is different than old style high sulphur Diesel, old Diesel would keep for decades as evidenced that Diesel in the South Pacific from WWII was used until long after the war, until it ran out.

Old style non alcohol gasoline would store for long periods too.

But we arenít burning yesterdayís fuels now are we.
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Old 25-04-2019, 09:20   #12
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Re: Diesel Fuel Tank

i would be inclined to make the fuel tanks totally independent. then you would need to switch the supply and return line too. you did not mention whether you wanted to reroute the fill line to the day tank.
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Old 25-04-2019, 09:48   #13
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Re: Diesel Fuel Tank

5 gal gravity feed tank (often referred to as a day tank) in a cockpit locker, t and valve it into your main feed to the engine......you might go 8 gal to have a little extra fuel......
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Old 25-04-2019, 10:07   #14
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Re: Diesel Fuel Tank

I recommend to add StarTron enzyme based treatment for diesel into the 40 gallon tank (for 40 gallons regular maintenance treatment), then top it off with good clean diesel.

Every year: add Startron and top off again.

This not only keeps the fuel good, it also provides you with a full tank at all times, which may be needed in emergencies or when the SHTF
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Old 25-04-2019, 10:28   #15
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Re: Diesel Fuel Tank

Quote:
Originally Posted by a64pilot View Post
Old style non alcohol gasoline would store for long periods too. But we arenít burning yesterdayís fuels now are we.

I can certainly buy ethanol free gasoline in my neighborhood but it is NOT cheap. Many use it for boats and motorcycles.
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