Diesel fuel lines

Jan 11, 2004
65
Hunter 31_83-87 Middle River, MD
I am replacing all the diesel fuel lines from tank to engine and back. Wondering what's the best way to get all of that air out of the fuel lines.
 
Aug 23, 2011
94
Hunter 31 Georgetown, MD
HI Tom H31
I would like to do the same thing. Can you tell me what size the diesel fuel line is and approximately what length to go both ways?
 
Jan 11, 2004
65
Hunter 31_83-87 Middle River, MD
For the Yanmar 2GM20F the fuel lines are 5/16" inside diameter. Length may vary depending on the layout of everything on your boat. It's best to measure accurately since the fuel hose is about $2.40/foot.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
start at the tank and chase the air bubbles forward to the injector pump. no need to bleed the return lines
 
Aug 23, 2011
94
Hunter 31 Georgetown, MD
Tom
Thanks for the reply. I'll climb in the "bunker" and measure it up first.
 
Jan 11, 2004
65
Hunter 31_83-87 Middle River, MD
So, to chase those air bubbles should I use a squeeze bulb or jog the engine, or some other method? My manual lift pump never seemed to work to bleed the engine.
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
oil extraction vacuum to pull the lines. Very easy
:plus:That is the way I did it. Then finished it off with the manual lift pump till I got fuel from the injector. Fired right up.

Be careful if your try the jog engine technique. Close the raw water inlet or you can get water into the engine. Not a good thing.:badbad:
 

HMT2

.
Mar 20, 2014
899
Hunter 31 828 Shoreacres, TX
We have a squeeze bulb and it is great for getting fuel in and air out, never have to use the manual lift pump when we change filters.
 
Jul 29, 2016
55
Hunter 31 Comox BC
Thanks for the info, needed to replace some of the fuel hose and want to install a squeeze bulb at the same time.
I forgot to measure the fuel hose before I left the boat this afternoon! I read somewhere it was 1/4" and here its 5/16".
Think I will go with here! Its for a 2GMF20 on my Hunter 31

Update: My Yanmar 2GMF20 had 1/4" fuel lines, replaced this morning.
 
Last edited:
Jul 22, 2011
146
Mariner Yacht Co.(NH) Mariner 28 Atlantic Highlands, NJ
Long shot, but when I needed to do mine I did not have the squeeze bulb handy. I quickly tired of trying to use the lift pump. I did have an unused metering pump for West system epoxy. It happened to fit the line perfectly, and bled the system very quickly. Maybe not the perfect solution, but good to know in a pinch.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
:plus:That is the way I did it. Then finished it off with the manual lift pump till I got fuel from the injector. Fired right up.
Ditto! I used my brake bleeding vacuum pump. Those hand vacuum pumps are great for lots of things.
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
We have a squeeze bulb
I have seen a variety of options used to simplify the bleeding process. We all know our boats are a series of compromises. Anything we add to the process can also backfire on us at the worst moment.

Concern exists with the bulbs. They work great until they develop a crack. Then they can leak like an open hose. Diesel is not too bad. Gasoline is an extreme hazard. Often you find the bulb attached to a small portable tank. The tank contains the fuel and the bulb is used to pressurize the system. All well and good. If a leak occurs, it is a small leak because the main volume of fuel is contained in the tank.

Introducing the bulb in line with an 85 gallon fuel tank on one end and an engine driven fuel pump on the other is a whole different story. That minor crack and seepage leak can be come a spraying fire-hose trying to fill your bilge with diesel or worse gasoline. So if you must add a bulb to your system mandate regular inspection and no compromise replacement at the first sign of cracks or leaks in the unit.

Best option is not to introduce air into the fuel lines when changing your filter. My old fuel filter was a Ford Truck filter spin on/off.
FilterOld.jpg
My first filter change was a nightmare. Not only did I enjoy a Diesel Fuel bath and spillage beneath the filter, the moment I cracked the seal air infiltrated everywhere into the system. I changed my filter system to a Racor 500M
FilterNew.jpg
I added the vacuum gauge to help me know when the filter need to be changed.
Now when it is time for a filter change I close the fuel lines, open the top, remove the dirty filter...
IMG_1169.JPG
replace the 2 O rings with the new ones provided.
Top off the filter with about 2/3 pint of fresh diesel. Close the filter top, and start the engine, no priming required.
Best time is under 7 minutes at sea, no spills.
 
Sep 11, 2015
147
Hunter 31 Marina del Rey
On my H31, I have 5/16 fuel lines and I use the lift pump lever to bleed it. I strongly advise against using a bulb to bleed as they do develop cracks. Another good solution is to use one of those kids water pump toys. I use it for the bilge, fridge, anything.
 
Feb 6, 2013
437
Hunter 31 Deale, MD
I used a vacuum pump on mine, with a length of clear tubing to prevent getting fuel into the pump, and a rubber nipple for the bleed hole on top of the secondary filter. I also filled the primary filters with fuel before installing them. I think it saved a lot of pumping time.
 
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Sep 5, 2010
40
oday 28 anderson
Hi All,
We have a ysm8 and added a racor 120 10um, replaced the 3 um filter on the motor and now we are having issue getting fuel to the motor. We used an oil extractor to try and prime the line. We were pulling fuel right before the injector. I was wondering if there could be an issue with this small motor pulling fuel through the extra filtration. Using the Manuel primer I could not ever get fuel through the bleed on top of the 3 um filter on the motor. Any suggestions?
 
Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
@blackout Have you verified the micron spec? I could not find a spec in the manuals.
Other possibility could you have a plugged screen on the end of the fuel pick up tube in the tank?
Could there be a blockage in the fuel lines?
Unlikely but is the fuel pump working?
 
Sep 5, 2010
40
oday 28 anderson
It has a mechanical fuel pump. We were able to pull fuel through the system with the oil extractor pump so that makes me think fuel is able to come out of the tank.