Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-14-2019, 07:55 PM   #1
Veteran Member
 
Djoub's Avatar
 
City: Parrish Fl
Country: USA
Vessel Name: Melody
Vessel Model: Mainship 350
Join Date: Apr 2018
Posts: 51
Fuel/Air leaks?

Sorry for the long post but I am hoping for some good info regarding fuel problems.
Boat is a 1998 Mainship 35 with a single 2008 Yanmar 370 hp bought less the a year ago. Original engine may have been gas. Engine has stopped a couple of times, once leaving me stranded on the water, second time was in slip. First time I thought it was dirty filters so all filters changed and bled system, everything worked for a couple of weeks. Second time no fuel to primary and secondary filters. Hired a mechanic and said I lost fuel to racor input, he primed everything and it ran good. A day later while looking around the engine room while it was running, I noticed air bubbles in the glass bowl at bottom. When I went to refill the racor, the fuel kept being slowly sucked down. Iím guessing it was leveling to the level of fuel in the tanks. It would only stop drawing when I shut off both supply values on the two tanks. I have a home made fuel polisher with a Gulf Coast Filter and a electric fuel pump, all by-passed for now with shutoff valves. A couple of weeks ago I moved fuel from one tank to another, donít remember how I left the valves but the next day both tanks were back to equal. Is this normal or do I need to close tank valves when engine is not running?
So I have 3 issues:
1) Bubbles in fuel stream while engine is running
2) Fuel flowing back into tank(s) with supply valve open
3) Small fuel leak somewhere in Port side tank area that canít be found.

Are all three problems related? I canít find any leaking using the paper towel method but I end up with a small amount near the stringer the tank sits on. All the fittings and clamps seem dry but as I said small leak somewhere near tank.
Someone mentioned could be a bad anti-siphon barb fitting on fuel tanks? Thinking of installing a temporary squeeze bulb on a short new hose from input of the racor, to a container of fuel or straight into one of the tanks and bypassing all the fittings and working back thru the system looking for bubbles.

Any thoughts on trouble shooting or ideas? Iím starting to think I should trade it in for a canoe Thanks
__________________
Advertisement

Djoub is offline   Reply With Quote
Old 03-14-2019, 10:02 PM   #2
Guru
 
City: Between Oregon and Alaska
Country: US
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 1,527
Most Racor housings I know of have check valves that should keep the fuel from back flowing. It could need cleaning or a rebuild kit. The lift pump has valves that operate as check valves and also should keep fuel between the lift pump and injector pump. If you have bubbles in the fuel while running you have an air leak. Somewhere before the bubbles. Many boats have a vacuum gauge at the Racor or between the Racor and the lift pump. It can tell you when the Racor filter is becoming dirty, if the lift pump is creating a decent suction when pulling fuel and if the needle jumps up and down when running, usually indicates a air leak. Air leaks are not usually constant. At higher speeds, and higher pump suction, fittings or lines that show no leak when sitting will allow air into the system. It's not easy to find the leaks. If you can't find the leak, add a air pressure fitting and put low air pressure into the lines and listen for the leak or look for spilled fuel. A bicycle pump is enough, 5+ psi usually shows or sounds the leak (if you have decent hearing).
Your tanks could have a equalizing line, unknown to you, that allows the fuel to flow between tanks. Fuel doesn't flow uphill, so the tanks need some connection below the fuel level to allow equalization. Hard to diagnose w/o a fuel diagram. Fuel polishing pump if properly installed should be able to run on not with the engine running without issue. The electric fuel pump also has valves that function as check valves. If it's tee'd after the Racor, the valves wouldn't allow it to interfere with the lift pump even w/o manual valves. I suspect in all your valves and bypassing, there's a hose fitting leaking at least air.
Another source for air is a bad diaphragm in a manual lift pump. Before complete failure, the pumps sometimes suck air thru the diaphragm from the crankcase.
As troubleshooting I'd replumb the electric pump as the lift pump and see if the problem goes away.
The fuel tank probably has to be pulled to find the leak. It will only get worse with time.
__________________

Lepke is offline   Reply With Quote
Old 03-14-2019, 10:32 PM   #3
Senior Member
 
City: MN and FL
Country: USA
Vessel Name: Serendipitous
Vessel Model: Mainship 390 and Bayliner 4788
Join Date: Feb 2013
Posts: 267
Quote:
Originally Posted by Djoub View Post
Sorry for the long post but I am hoping for some good info regarding fuel problems.
Boat is a 1998 Mainship 35 with a single 2008 Yanmar 370 hp bought less the a year ago. Original engine may have been gas. Engine has stopped a couple of times, once leaving me stranded on the water, second time was in slip. First time I thought it was dirty filters so all filters changed and bled system, everything worked for a couple of weeks. Second time no fuel to primary and secondary filters. Hired a mechanic and said I lost fuel to racor input, he primed everything and it ran good. A day later while looking around the engine room while it was running, I noticed air bubbles in the glass bowl at bottom. When I went to refill the racor, the fuel kept being slowly sucked down. Iím guessing it was leveling to the level of fuel in the tanks. It would only stop drawing when I shut off both supply values on the two tanks. I have a home made fuel polisher with a Gulf Coast Filter and a electric fuel pump, all by-passed for now with shutoff valves. A couple of weeks ago I moved fuel from one tank to another, donít remember how I left the valves but the next day both tanks were back to equal. Is this normal or do I need to close tank valves when engine is not running?
So I have 3 issues:
1) Bubbles in fuel stream while engine is running
2) Fuel flowing back into tank(s) with supply valve open
3) Small fuel leak somewhere in Port side tank area that canít be found.

Are all three problems related? I canít find any leaking using the paper towel method but I end up with a small amount near the stringer the tank sits on. All the fittings and clamps seem dry but as I said small leak somewhere near tank.
Someone mentioned could be a bad anti-siphon barb fitting on fuel tanks? Thinking of installing a temporary squeeze bulb on a short new hose from input of the racor, to a container of fuel or straight into one of the tanks and bypassing all the fittings and working back thru the system looking for bubbles.

Any thoughts on trouble shooting or ideas? Iím starting to think I should trade it in for a canoe Thanks

FYI, no Mainship Trawlers were ever shipped with gasoline engines. Curious as to what made you think it was repowered? Possibly it had one of the notorious Cat motors and a previous owner repowered with Yanmar?



1) Air-bubbles: You appear to have a leaking fuel line. Your engine is dying because diesel engines cannot tolerate any air whatsoever in the fuel stream.


2) Fuel flowing back into the tank...: This is normal. Diesel engines do not use all the fuel that is pumped into the injection system. The excess fuel goes back into the tank(s).


3) Fuel leak: Gotta find it and fix it.


Cheers!
__________________
RiverGuy~~
Riverguy is offline   Reply With Quote
Old 03-15-2019, 07:27 AM   #4
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 19,528
IF you can keep the fuel system pressurized ,from tank to engine, pump or hand bulb, the leaks will show up on the paper towel teltales.
FF is offline   Reply With Quote
Old 03-15-2019, 07:16 PM   #5
Veteran Member
 
Djoub's Avatar
 
City: Parrish Fl
Country: USA
Vessel Name: Melody
Vessel Model: Mainship 350
Join Date: Apr 2018
Posts: 51
Ok, thanks for the tips.
To answer a couple of questions;
I understand the fuel return concept of diesel, all references are to supply side. Air bubbles are on the input side of racor. Increase in bubbles when engine is revered above ideal. Doesnít seem to be any issues after racor to lift pump and eventually FIís except when the air in the racor pushes down to the output fitting then it effects engine stall.
There is no dedicated equalizing connection (there are fittings in tanks but never punched out). However, as I look at the plumbing and diagram, both tanks tie together with teeís, so essentially if both tank valves are open they should/will equalize.
I also counted 37 hose clamps, 54 pipe fitting interfaces, and 14 valves. If there is a leak in one place it is going to be hard to find. Looking at how messed up and complex things are Iím thinking about removing everything and starting from scratch and keeping it simple with no polisher. Simple 4 way valve for Port/Stb/Both/Off same for return line.
Lots of things done wrong, B2 type hoses and some no name hoses on return lines, teflon tape everywhere, not even sure the valves are proper type for fuel application.
See attached pic, one is the polisher, the other is a return line. lots more fittings then shown.

Thoughts on remove and replace? Is that too much for a DIY or should the pro be called in?
Thanks again
Attached Thumbnails
Click image for larger version

Name:	9D973D74-217B-44EE-A485-7B9466B3DBAC.jpg
Views:	42
Size:	114.5 KB
ID:	86441   Click image for larger version

Name:	EEB879ED-F4A7-4FE5-8ECA-9A062FB48DD1.jpg
Views:	38
Size:	178.8 KB
ID:	86442  
Djoub is offline   Reply With Quote
Old 03-15-2019, 11:55 PM   #6
Guru
 
Comodave's Avatar
 
City: Au Gres, MI
Country: US
Vessel Name: Never Say Never
Vessel Model: President 41 DC
Join Date: Jul 2015
Posts: 5,084
Replacing the whole system is certainly within a DIY capability. I did it on a previous boat that we replaced the fuel tank. Not too hard if you have room to work in. With a single you should have adequate room to work. Good luck.
Comodave is offline   Reply With Quote
Old 03-16-2019, 12:26 AM   #7
Guru
 
City: Between Oregon and Alaska
Country: US
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 1,527
Before starting over you should try pressurizing with air. I've found a lot of air leaks that way when all else failed.
__________________

Lepke is offline   Reply With Quote
Reply

Tags
air leak, fuel leak

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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





All times are GMT -5. The time now is 09:15 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012