Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 25-04-2020, 15:08   #16
Registered User

Join Date: Feb 2010
Location: US
Boat: Sunward 48
Posts: 151
Re: Fuel Return Line Questions

Quote:
Originally Posted by Locquatious View Post

*Can air in the fuel return line, assuming it can flow till empty of fuel, allow air to get into the injectors while the engine is at rest?
Actually, the M673 generator has a check valve between the bleed off return line passing by the injectors and the injector pump. I disassembled that portion and found some dirty fuel in that check valve. There is a possibility that the check valve did not seat which would allow air from the return line to enter the injection pump.

For those who might say I'm not changing filters enough, be kind. The boat was 50° over on it's side after Irma. The check valve ball may not have been seated properly for several months till the boat was righted.
__________________

Locquatious is offline   Reply With Quote
Old 25-04-2020, 15:36   #17
Registered User

Join Date: Feb 2010
Location: US
Boat: Sunward 48
Posts: 151
Re: Fuel Return Line Questions

Quote:
Originally Posted by MicHughV View Post
...sometimes your best bet is to have a qualified diesel mechanic come and look at your problem.
During the pandemic it is harder to get qualified help. Some mechanics don't like compromising social distance on boats. I have been in touch with an excellent mechanic by e-mail and I have found one qualified mechanic who came out. He did check the start battery- great shape. He concluded compression is not the problem. He advised re-plumbing all the fuel feed system. Two tanks, two Racors, two engines, two lift pumps. That's a major project that requires going to supply stores multiple times to get the right fittings, valves, and hoses. I am in the Caribbean and one parts store won't let anyone except employees in the door. I had the parts to do the return line upgrades but not the supply rebuild.

Sometimes we're on our own. If the gen doesn't start, we lose refrigeration. The boat yards are closed so we can't get out of the water and go home. We can't move to other countries. We have to do our best with our own mechanical skills. There is YouTube, websites, manuals, and the Cruiser's Forums. DIY is best.
__________________

Locquatious is offline   Reply With Quote
Old 25-04-2020, 18:30   #18
Registered User
 
AndyEss's Avatar

Join Date: Dec 2016
Location: Sea of Cortez/northern Utah/ Wisconsin/ La Paz, BCS
Boat: Hans Christian 38 Mk II
Posts: 630
Images: 1
Re: Fuel Return Line Questions

Small diesel engine fuel injectors don’t run at 36,000 psi - you got a decimal place wrong.

For my VW Pathfinder (50hp 4 cyl) the fuel injectors open at about 2,800 psi. The compression ratio of the cylinders is 23:1, so the backpressure on the injector is at most about 325 psi.

Diesel engines are not ultra-high pressure bombs just waiting to go off. On the other hand 2800 psi is nothing to sneer at - a leak in a pressurized fuel line will easily penetrate skin and inject diesel directly into your body.

Be careful with diesel fuel systems.
AndyEss is offline   Reply With Quote
Old 25-04-2020, 18:47   #19
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 11,039
Re: Fuel Return Line Questions

Quote:
Originally Posted by Locquatious View Post
.......
Sometimes we're on our own. If the gen doesn't start, we lose refrigeration. The boat yards are closed so we can't get out of the water and go home. We can't move to other countries. We have to do our best with our own mechanical skills. There is YouTube, websites, manuals, and the Cruiser's Forums. DIY is best.
I get it .

From your descriptions so far, I don't think there is anything wrong with your return line although that check valve you mentioned upthread might be an issue.

Although there are differences between engines, as a generalisation many small marine diesels are similar in operation.

The lift pump will provide way way more fuel than the injector pump needs with the excess being simply diverted into the return line. If your injector pump has a return line connected, you can almost be sure it operates this way. If the injector pump does not have a return line connected, then it doesn't - obviously.

As a test, you could (most likely) be able to set up a gravity feed directly into the injector pump. Even just a funnel and some tube is all that is needed for testing purposes. If the engine keeps it's prime between starts, then you have a small air leak somewhere between the main tank and the injector pump. Keep moving the temporary gravity feed back towards the tank until you discover where the problem starts again.

FWIW, gravity feed fuel leaks out in the same spot where air leaks in when using a lift pump but leaking fuel is easier to see than leaking air.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 25-04-2020, 18:50   #20
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 11,039
Re: Fuel Return Line Questions

Re injector pump pressures. A mechanically injected small diesel will usually be in the order of 2,500 psi while an electronic common rail injection will be ten times that.

As some others have noted .
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 25-04-2020, 19:18   #21
Registered User

Join Date: Feb 2010
Posts: 612
Re: Fuel Return Line Questions

Quote:
Originally Posted by Locquatious View Post
During the pandemic it is harder to get qualified help. Some mechanics don't like compromising social distance on boats. I have been in touch with an excellent mechanic by e-mail and I have found one qualified mechanic who came out. He did check the start battery- great shape. He concluded compression is not the problem. He advised re-plumbing all the fuel feed system. Two tanks, two Racors, two engines, two lift pumps. That's a major project that requires going to supply stores multiple times to get the right fittings, valves, and hoses. I am in the Caribbean and one parts store won't let anyone except employees in the door. I had the parts to do the return line upgrades but not the supply rebuild.



Sometimes we're on our own. If the gen doesn't start, we lose refrigeration. The boat yards are closed so we can't get out of the water and go home. We can't move to other countries. We have to do our best with our own mechanical skills. There is YouTube, websites, manuals, and the Cruiser's Forums. DIY is best.


Duplicating the fuel system is probably not the best first step, and the little non return valve is an important part of the system because it does connect and disconnect the return circuit to the supply from the filter head.......but have you tested the glow plug circuit and individual glowplugs. NL’s are a bugger to start from cold if they’ve been standing for a while. Is the fuel tank lower than the engine or higher?
An optional fuel supply solution might be to install a day tank for the genset, this was once a fairly common arrangement but requires quite a lot of real estate for a 4 gallon tank but provides a positive head for the generator and if you filter the fuel into that tank it will always be a known clean tank.
Pete.
skipperpete is offline   Reply With Quote
Old 25-04-2020, 21:02   #22
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 3,613
Images: 7
Re: Fuel Return Line Questions

Quote:
Originally Posted by Wotname View Post
Re injector pump pressures. A mechanically injected small diesel will usually be in the order of 2,500 psi while an electronic common rail injection will be ten times that.

As some others have noted .
I knew they were higher but thought about 6,000-7,000 psi. We are not mislabeling kPa are we?

And it sounds like another good reason not to have common rail in a boat. A small leak with a bunch of atomized diesel in an engine box with electrics sound a bit bombish to me.
RaymondR is online now   Reply With Quote
Old 25-04-2020, 21:15   #23
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 11,039
Re: Fuel Return Line Questions

Quote:
Originally Posted by RaymondR View Post
I knew they were higher but thought about 6,000-7,000 psi. We are not mislabeling kPa are we?

And it sounds like another good reason not to have common rail in a boat. A small leak with a bunch of atomized diesel in an engine box with electrics sound a bit bombish to me.
Nope https://en.wikipedia.org/wiki/Common_rail

At those pressures, they don't like dirty fuel either
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 29-04-2020, 06:22   #24
Registered User

Join Date: Feb 2010
Location: US
Boat: Sunward 48
Posts: 151
Re: Fuel Return Line Questions

As a follow-up, the generator is running much better now. The biggest change was replacing the glow plugs. It is surprising that glow plugs are needed in the tropics. But the earlier combustion during start aids the starter motor turning over the engine.

Other changes were made. All fuel connections were tightened. A weeping shut-off valve was replaced. A second boost pump was installed since the bottom of the fuel tank is 45" below the inlet of the generator. Northern LIghts specifies 39" as the max, but that is probably for shorter fuel lines.

Thanks for all the advice and help.
Locquatious is offline   Reply With Quote
Old 30-04-2020, 12:42   #25
Registered User

Join Date: Jul 2010
Location: Oriental, NC
Boat: None
Posts: 129
Re: Fuel Return Line Questions

*Can air in the fuel return line, assuming it can flow till empty of fuel, allow air to get into the injectors while the engine is at rest?

YES. IF the fuel return line is running down hill and empties out it can allow air backways into the injectors via the return rack. Run the hose with a lower loop before entering the tank so that it does not empty out from gravity. Does it happen all the time on all engines? NO. But it can create a pesky starting issue that is intermittent and very gremlin like.

*Should the fuel return line slope down to the tank or can there be low points prior to entering the tank?

Add a loop per above.


*If the return line of a generator is teed into the return line of a main engine, can the fuel return flow of the main engine create a suction on the return side of the generator such that air is pulled into the generator fuel supply system?

Maybe/maybe not but I like to keep systems separate to avoid this kind of thing. It can really complicate diagnosing problems in the future
FPNC is offline   Reply With Quote
Old 30-04-2020, 14:23   #26
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 38,198
Images: 241
Re: Fuel Return Line Questions

Northern Lights Models M673l , M673ld2, M673l3, and M673ld3

OPERATOR'S MANUALhttps://www.northern-lights.com/medi...fs/OM673L2.pdf

PARTS MANUALhttps://www.northern-lights.com/medi...dfs/P673-2.pdf

INSTALLATION MANUALhttp://www.ironbarque.net/Boat%20Doc...Manual1000.pdf

I encourage anyone, who downlaods useful documents, from links (links often go ‘dead’ with time), to then upload the document to our
CF Document Library Downloads:https://www.cruisersforum.com/forums/downloads.php
__________________

__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Reply

Tags
fuel

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Does diesel fuel return line have to be above fuel tank? er9 Engines and Propulsion Systems 31 01-06-2018 13:59
fuel line return issue Autumns Wind Engines and Propulsion Systems 11 23-01-2014 10:07
Fuel return line on tyamnar 4jh3e stevensuf Engines and Propulsion Systems 0 01-06-2013 08:35
Electric Pump in Fuel Return Line banjoship Construction, Maintenance & Refit 10 12-08-2012 15:56
fuel return line Han Engines and Propulsion Systems 17 17-06-2008 02:58

Advertise Here


All times are GMT -7. The time now is 23:21.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.