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Old 04-04-2021, 17:04   #1
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Need a sense check on siphon feed diesel supply.

Ok bit of a story,

My 1968 Columbia 36 is soon to be splashing again after spending winter on the hard. I bought her last fall and motored her a couple hours to new marina, without any issues with engine or diesel system. Boat has a 12-15 year old Yanmar 3gm30 that seems to be in excellent shape. I am assuming at the same time they installed a new diesel tank (poly tank) that is mounted on a shelf in aft cockpit locker. They self is roughly same height as cockpit floor so the diesel tank is mounted higher up then the engine. This winter I noticed that the self (raw plywood) was half rotten so this winter I simply replaced the shelf with epoxy sealed plywood. I didn't want to go re-engineering diesel tankage. So the quick and easy solution was to simply replace the shelf with new plywood. Figuring it worked well for previous owner so........

Today I completed that task, re-installed the diesel tank (about 28 gallon tank), connected the supply and return lines. And that is when the problems started....... Those lines feeding into the engine compartment (which again is lower then the tank. Bottom of tank is roughly same height as cockpit floor and obviously engine is under the same floor. So supply line first goes into a shut off valve that is attached to a Racor filter and water separator. So when supply lines are full of diesel they are syphon gravity feed down. So normal process to change the Racor would be shut off valve open bleed valve and bottom drain. Reassemble and reopen shut-off valve and bleeder which siphon fills the everything. Unless you run out of diesel system primes by gravity feed. So I guess the Racor pump probably hasn't been used in a very very very long time. It was siezed and once freed didn't pump anything to get flow started. After a bunch of testing and figuring this out I actually used air to pressurized the tank just enough to get the diesel flow started and eventually got everything bleed. So Yanmar is back to funtional and operating the same way it has for a long time.

However, now that I fully understand the system I am debating options and possible problems. First a fuel leak would siphon empty the diesel tank into bildge..... That would of course be bad, so I will be very careful about turning off the shut-off valve, but I do have to move stairs, open hatch, lay on floor, turn valve... You get the point. I will also mention that there is also a water tank on other side of boat to balance against the weight of diesel on port side. There are of course some positives like once you get the supply line full of fuel gravity takes care of priming systems (no little pumps to worry about) Now I do need to fix or replace the Racor so pump works, pressurizing tank worked but isn't great solution if I ran the tank a little too, but it got me ready to splash in the next week or so.

My hope is to simply use system like it is now for this season, get some good experience on the boat before I go making any major system changes. That seems OK to me, but hoping for a sense check from the community. What potential risk am I not thinking of with diesel tank mounted so high up and having a gravity fed system?

Thoughts?
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Old 04-04-2021, 17:27   #2
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Re: Need a sense check on siphon feed diesel supply.

Quote:
Originally Posted by Fishzine View Post
Ok bit of a story....

....My hope is to simply use system like it is now for this season, get some good experience on the boat before I go making any major system changes. That seems OK to me, but hoping for a sense check from the community. What potential risk am I not thinking of with diesel tank mounted so high up and having a gravity fed system?

Thoughts?

Iti is a bit of an unusual arrangement for a smallish sailboat, but only because the hull design usually doesn't allow it. Having a tank above the engine level is by no means bad or even that rare. My current boat, and my last boat, both have tanks that are above the engine. if not all the time, when they have any significant level of fuel.

I'd suggest that you fix the priming pump in the Racor, when functional it will handle the task of lifting the fuel up and over and starting flow.

Leaks are bad in any fuel system. Take good care, and don't sweat it.
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Old 04-04-2021, 22:40   #3
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Re: Need a sense check on siphon feed diesel supply.

Agree with bilkinny, dont sweat it too much. Have seen a few boats with day tanks that just gravity feed the engine. It's a safer way really except the day tanks tend to be small so you can end up running out of fuel if you are not careful. You can get an solenoid valve to be your fuel shutoff valve so you can just flick a switch to avoid your access difficulties.
The other thing you can do if you cant fix the racor pump is to get a little inline electric lift pump, they are very cheap. We have one to help bleed our filters as the priming lever on the Yanmar lift pump is a PITA.. Well actually we use a squeeze bulb but its on the plan to replace with the electric pump.
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Old 05-04-2021, 10:34   #4
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Re: Need a sense check on siphon feed diesel supply.

+1 on Compass790 advice. We carry one of these little gems, screwed down on the fuel side of the engine, as an ultimate backup for failure of the mechanical lift pump. We have not needed it during the last eight years, but I'm not going to throw it away. It costs $12.

https://www.amazon.com/JDMSPEED-Univ...s%2C231&sr=8-3
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Old 05-04-2021, 19:58   #5
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Re: Need a sense check on siphon feed diesel supply.

Thanks for all the feedback. Feeling better about using the system as is for now. I like the idea of a small priming pump to avoid the pump on the racor or the yanmar. Will look at this vs fixing the manual pump on the racor. Before I figured out the racor pump wasn't working spent way too much time doing boat yoga trying to push and pull that stupid lever up and down..... Hate to think of doing that in a rough sea condition trying to re-prime the fuel system......

For now however, Feeling better at starting off this season as is.
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Old 10-04-2021, 01:55   #6
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Re: Need a sense check on siphon feed diesel supply.

To the original poster,
BTW, Raycor filter elements are inordinately expensive, like $40-50!
Also the clear plastic bowls are prone to cracking. They are no better than any other quality diesel filter, but somehow have gotten to be associated with “marine” use.
Since your Raycor filter pump is kaput anyway, a much better option is a generic truck diesel filter/water separator, available from any good auto parts store. The one I use has a glass bowl and the filter elements cost about $8. You don’t need a priming pump on the filter, just another potential source of air leaks. As other have commented, get a cheap electric fuel pump.
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