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Old 07-18-2014, 05:11 PM   #1
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Gravity feed fuel system

If I was to rig a separate fuel system for testing and to run several miles from the yard to my new moorage would I need to install a "lift pump" as usual? My dedicated fuel can/tank is a 5 gal solvent can w a valve and fittings at the near bottom to join w the fuel hose. The can will be 2.5 to 3' above the injector pump. The engine is a simple 37hp Mitsubishi 107 cu in NA engine fairly new.

It would seem to me the fuel pump would not be necessary or even desirable but perhaps the fuel injector pump needs the 5 or so pounds of pressure to operate properly. What say to someone who knows .... like David.

Wish I was still on BoatDiesel.com but many here are.

Tom what do you think?
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Old 07-18-2014, 05:18 PM   #2
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Isn't the lift pump factory mounted on your engine now?
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Old 07-18-2014, 08:23 PM   #3
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If you can bypass the lift pump and keep the fuel level above the injection pump,then it will run.I can't vouch for how good.I've seen friends do it on equipment with diesel engines.
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Old 07-18-2014, 08:26 PM   #4
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Quote:
Originally Posted by manyboats View Post
If I was to rig a separate fuel system for testing and to run several miles from the yard to my new moorage would I need to install a "lift pump" as usual? My dedicated fuel can/tank is a 5 gal solvent can w a valve and fittings at the near bottom to join w the fuel hose. The can will be 2.5 to 3' above the injector pump. The engine is a simple 37hp Mitsubishi 107 cu in NA engine fairly new.

It would seem to me the fuel pump would not be necessary or even desirable but perhaps the fuel injector pump needs the 5 or so pounds of pressure to operate properly. What say to someone who knows .... like David.

Wish I was still on BoatDiesel.com but many here are.

Tom what do you think?
what about the return line?
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Old 07-18-2014, 11:05 PM   #5
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There should be a supply pump as part of the fuel system that charges the high pressure pump. As I remember the specs on different systems were anywhere from around 10 psi to 70 psi. Without the proper charge pressure on the system it won't run like it should or not run at all.
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Old 07-19-2014, 12:24 AM   #6
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what about the return line?
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Most are plumbed back into the filter.Those that aren't would be a bit more difficult to bypass the return line to go back to the temporary tank.
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Old 07-19-2014, 06:58 AM   #7
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I would think on a small, naturally aspirated diesel gravity feed should work just fine...I know it does on Lehmans and small Yanmars and pretty sure it did on my 3208 Cats at least at low power settings. The more demand the higher the head pressure sometimes.

The only issue I can think of is if going through the secondary filter and the restriction was greater than what the injection pump demanded.

The real answer lies in your injector pump and you may have to ask the manufacturer for some specs on it.

Most returns are plumbed back to the tank for cooling purposes I think..some boats are rigged where it returns into the fuel system but those have been rare in my experience and usually only with engines like the Lehman 120 that have very small amounts of fuel returned compare to what's burned.
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Old 07-19-2014, 10:02 AM   #8
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Thanks all for for your input.

RC that's what I thought and I'll call them Monday. The electric "lift pump" is the Facet we discussed on another thread. I don't know if there was a mechanical factory lift pump. The engine came from and is a Mitsubishi. It was built as an industrial engine. The marineizers (Klassen now defunct and bought out by Hatton) put the little electric pump on and it only produces 4 or 5 psi. How much pressure would a 2' "head" create? Probably much less than 4 psi but ?

Hollywood,
HaHa .. yes I thought of that but not at first. Was embarrassed when I realized I was about to pump my 5 gallons in the temporary tank right into the boat tank. No harm would be done but for a moment I'd sure wonder how my fuel got burned up so fast. Not to mention I'd be dead in the water someplace. Probably tied to the float at the yard though. Yes I'll have to rig up a return line up to the 5 gal can/tank on the settee. Haven't done that yet.


ben2go,
Yes that's where I got the idea ... on youtube. Guys selling old diesels running them on a pallet holding a fuel line w a little funnel stuck in the end.


I made this post because everybody I asked about re this gravity feed running seemed not 100% sure on the matter. RC ans psneeld seemed sure of their view and I'm sure ther'e right except for the higher pressure RC mentions but that 10 to 70 lbs pressure is probably just as necessary on my little Mitsu just considerably less pressure. Just don't know.

My whole reason for doing this is that I've had a ghost fuel delivery problem for years that (on my trip from AK 2 years ago) resulted in a near engine out and one complete engine failure. I think the problem stems from the way the mechanic plumbed the fuel system before we left for AK. In the fuel and clinging to parts like hose barb fittings I've seen strands of stuff I believe is remnants of Teflon sealer tape and perhaps chunks of the putty like sealer that was also used. I've seen so many people .. mechanics included slap on some goop or T sealer tape with no regard for the possibility of some remnants falling away from the fittings and be free in the fuel system. Of course then the globs of soft sticky stuff and stringy strands of T tape is free to ride along in the fuel flow to wherever it goes. Obviously anything like that running into the fuel pump (mechanical or electric) would likely get stuck on or tangle up on the little flutter or flapper valves in the fuel pump degrading it's pumping abilities. One little glob of the putty like sealer could (definitely IMO) shut down a fuel pump. Something that shoots this theory down though is the fact that nothing like that was found in the high pressure pump that was sent off to the big diesel shop ., probably Nanimo. And the engine has never run rough or temporary lost a cylinder so it's unlikely any foreign matter ever got to a cylinder injector.

But ... I want to re-do the whole system. But temporarily I want to rig up a system that will run the engine from the yard to the new moorage. I would like to have at least half power to do that and I may need the temporary system to take the boat closer to a mechanic like North Harbor Diesel in Anacortes. Or for whatever I want the boat operational.

The reason I don't want to use the original pump is that it was in the old system and may be contaminated w sealer remnants. I have two new fuel pumps but I'm not wanting to use them as they could become contaminated and I intend on installing them in parallel in the new system.

Scott,
On Lehmans and small Yanmars when run totally by a gravity feed like a motorcycle are they capable of significant and long lasting loads? Or was the experience you spoke of just low speed and no load?

Sorry about the long post.
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Old 07-19-2014, 10:34 AM   #9
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My only experience is at low loads as in emergencies and I guess the head and filter restriction were OK. I doubt the duration is important ...you just need to deliver more fuel than the injector pump needs.

Browsing many diesel forums and posts outside the marine community confirmed what I though too...some portable gensets and light towers, lit road sign gensets...etc..are all run by small industrials like your Mitsubishi and are gravity fed from tanks mounted above or off to one side but above the injector pump. They are all running at design load for long periods.

Maybe I've just seen a small fraction of possibilities and the references may have been about older equipment...but I don't think so.

If you are worried...the formula for head psi is about a meter for every psi. just mount your portable tank on your cabin top with a long hose and you should be up mear 3 psi which should be enough pressure. Check it at the dock under 1/2 throttle against some lines if you are concerned.
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Old 07-19-2014, 10:56 AM   #10
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Eric

One foot of head for water is .545 psi as best I recall. Diesel fuel will be less by about 15%.
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Old 07-19-2014, 11:42 AM   #11
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Not sure what value if any this will be for you Eric but this PDF contains what CAT feels is needed in an effective fuel delivery system.

http://pdf.cat.com/cda/files/3375312...EBW4976-04.pdf
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Old 07-19-2014, 12:15 PM   #12
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DD 71 series I believe required 30 to 70 psi from its gear type supply pump, Murphy diesels which had the patent on the unit type injectors that DD used was also in this range. On your engine (SL series mitsubishi?) the electric pump will supply the volume & pressure required to run. If that pump goes bad even if you have gravity feed I doubt if it'll rev very high, it'll run like a fuel filter is plugging up. Detroit and cat both used gear type supply pumps and over the years I replaced & rebuilt many of them, always carried a spare pump and check valves on my truck. Cat used to have a gauge on the dash that gave a indication of when to change fuel filters, here is a pic of a Cat gauge, as the filter plugs the psi drops especially when under a heavy load and the govenor is giving full fuel.
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Old 07-19-2014, 12:31 PM   #13
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The answer is pretty simple, just hook up a 12v pump from your gravity tank to the engine and be on your way. You could pretty easily wire it to only run when the engine is running.
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Old 07-19-2014, 03:23 PM   #14
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Hey you guys are great. Prolly won't be ask'in mechanics many questions in the future. I've got TF!

Scott my little Mitsubishi is generally running a gen and not a prime mover often. I don't know if they used the 12v Facet pump on the gen sets or used gravity feed. The Klassen guys are almost all at Hatton so I could call them too. From your post I'm inclined to go w gravity. I'm not concerned about the filter resistance ... It's 30 micron.

Tom good to hear from you. Where are you now?
I've written off the roof for head idea.

Craig I'm at Starbucks and the wi-fi is too slow here.

RC yes it's an SL. Seems to be a good engine and very basic. When the engine falters that's how it runs .. Like a filter's plugged. And yes that's another reason I think it should run fine is that most of these engines go to gen sets or little front end loaders ect. All probably gravity feed. That's a good idea for me RC ... The fuel pressure gauge!

CaptBill11 that's how Klassen set the engine up ..... W the little 4 psi 12v electric pump. I just want to use gravity feed temporarily.
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Old 07-19-2014, 04:54 PM   #15
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Quote:
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CaptBill11 that's how Klassen set the engine up ..... W the little 4 psi 12v electric pump. I just want to use gravity feed temporarily.
I get that. But if it's just to keep any junk from getting into the fuel system, use a new pump and then you don't have to worry about any junk in the fuel or whether you can run the engine at full RPMs.

Unless I'm missing something, like you just want to see if it will work, I don't see the point of messing with the gravity feed only setup.
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Old 07-19-2014, 06:19 PM   #16
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Eric

One foot of head for water is .545 psi as best I recall. Diesel fuel will be less by about 15%.
That would be very salty water. Fresh water is 0.433 psi/foot. Diesel is 0.360 psi/foot.
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Old 07-19-2014, 06:33 PM   #17
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That would be very salty water. Fresh water is 0.433 psi/foot. Diesel is 0.360 psi/foot.
When I was looking I saw a few different numbers which I didn't understand..I figured it would be locked...so it surprised me.

More than several gravity feed suggestions said about a meter per 1 psi which isn't exact but a good rough estimate....
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Old 07-19-2014, 09:47 PM   #18
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Psneeld wrote;
"More than several gravity feed suggestions said about a meter per 1 psi which isn't exact but a good rough estimate.... "

One only needs what one only needs. Close enough is just that and anything more is a waste of time.
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Old 07-23-2014, 02:35 PM   #19
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The easiest no pain fuel tank is an outboard tank with an inline bulb pump.

All you probably need is 1 gph of fuel , so pumping by hand if large power is needed would be no hassle.

The coasties use an 11 ft head to create 5psi for tank checking.

So mounting the OB tank on the cabin top and using the bulb to find any air leaks and prime the beast should do the job.

Happy trails,
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Old 07-23-2014, 03:06 PM   #20
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Hi Fred,
And thanks. Your timing is great as I just put fuel in the tank yesterday and it leaks .. at the welded fitting. Tom suggested I put the tank on the roof too. There's the return line to consider also. Decided to get some JB Weld and patch-seal the welded fitting.
Like most projects this is more trouble than I though it would be.
The OB tank is a great idea and I have several old ones. I can always dump the gasoline into the old suburban. But/and unless it was a really old tank I'd need to run w the cap off and the return line going in the filler hole. I'm in town and I'll get some JB Weld so I have that option.
For those still wondering about the pump I've talked to more people (most very experienced) and Scott is the only one positively saying it will work but only on Lehmans and one or two others. I've rigged the inlet system including the pump so all I've got left is the tank. The hose is ready to go for the return line too.
Now if I can get the pump wires back together right .... I think it must ground from the mounting base flange but I know there were more than two wires hooked up. I made notes that I haven't lost. I glanced at then and aren't sure I can sort it out from the notes. I'll take my volt meter when I go.
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