Help...dead in the water, air in fuel lines!!!

FF said:

"One thing on my list now is to install a return line from one side to the other."

The better technique is a genuine ganged fuel valve that has the ability to switch both the fuel supply and return . No thinking , no problems.

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A. Tank isolations valves.
B. cross connect valve to keep the fuel levels equal, shutting this valve when there is contaminated fuel in one tank
C. a fuel return valve from each engine and generator to both tank you wish. Will help with trimming the boat. If it was necessary to isolate a tank due to contaminated fuel, you want to be able to return the clean fuel to the supply tank.

Of course we did not install the valves necessary for the fuel polishing system.


I think that does it.

I didn't read every post here, but Ill just add that I recently went through fixing an air leak in my fuel system. The number one thing I added to my fuel system is a squeeze bulb placed motor side of the racor. It allows you to bleed a completely dry system all the way to the injector pump in about 5 minutes total for both motors. No electrical needed, no more messing with the lift pump lever in frustration ext.. I no longer worry about changing the Sims filters on the motors, or replacing/inspecting fuel lines - its easy now.

CEC said:

I didn't read every post here, but Ill just add that I recently went through fixing an air leak in my fuel system. The number one thing I added to my fuel system is a squeeze bulb placed motor side of the racor. It allows you to bleed a completely dry system all the way to the injector pump in about 5 minutes total for both motors. No electrical needed, no more messing with the lift pump lever in frustration ext.. I no longer worry about changing the Sims filters on the motors, or replacing/inspecting fuel lines - its easy now.

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Is the squeeze bulb in the primary fuel line or do you redirect the fuel with valves when the bulb is needed? (Ie is fuel flowing through it all of the time?)

Yes its in the primary lines one each after the racor. I'm using the good ones about $12 each. I have researched and followed up with ABYC surveyors and a friend that's in the guard. I'm told they are fine for use with diesel below deck but NOT for gas. One of the surveyors I spoke with also has them on his boat. There's tons of controversy on the topic, but for me its more of a safety issue NOT having them. Use at own risk like everything else..

A second advantage of a fuel bulb from the tank feed is searching out air leaks.

With a bit of pressure fittings and gaskets that might leak are easily found by using a strip of paper towel tied to every fitting and component.

If there are no fuel leaks in 24 hours , the system is probably air tight.

A cheesy rubber bulb, in-line with the main fuel system that contains hundreds of gallons...what could possibly go wrong?

Isolate it in a loop with two valves and select it when you need it, just like a sight tube. Same with an electric pump.

I agree that I would isolate the bulb. My tanks would gravity drain most if not all of the fuel if the bulb broke.

“If the bulb broke”

Not being argumentative however is there any more probability of having the bulb break vs having a fuel line rupture? If the bulb is good quality CG approved material like the CG approved fuel line, logic would tell me probably not? I agree that having a bulb in line still feels a little awkward.

Interesting post.
The first thing I would be inclined do is to fit a shut off valve at the tank with non return valve directly on to it, because between the tank and filter is a long line and you have to build sufficient vacuum to lift the fuel, if you stop to pump the fuel will run back.
If using CAV sandwich type filters I would fit the modified filter head with 'spin on' filters incorporating a 'heel of the hand' button pump.
Bleeding the engine is child's play then, simply put fuel in the tank and pump until the button goes stiff, then slacken ALL injectors lines, open the throttle full, and crank the motor.
If you have crew get them to pump the button pump while your cranking the motor but be ready to close the injector lines and throttle pdq when she starts to fire.

"I agree that I would isolate the bulb. My tanks would gravity drain most if not all of the fuel if the bulb broke."

On some boats the fuel supply line is taken from the top of the tank which may be higher than the engine.

So a leak in the fuel system could syphon the tank empty.

only loosen injector lines if you have to.


some engines fuel don't require it because of bleeder screws or other auto bleed bleed features.


learn what you have so it makes it easier on you

Cigatoo said:

Why do you not feed from both tanks at the same time?

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Two reasons:
Primarily if i have a fuel problem, let's say i see something in the filters, I immediately switch tank feeds, drain, change filter, then try to figure out what's going on. If i'm feeding from both tanks, how do i do that?

Secondly, my returns are not equal. For whatever reason, if both returns are open, it will put most fuel in stbd tank, running the port tank dry.

And related to both issues, if you hande a problem in one tank and your feeding from and returning to both, you now have contaminated the good tank.

Unless, i'm crossing an ocean, I also only fill one tank at a time from the same source. Then, once in the tank, I'll run the fuel polisher a bit and if ok, only then equalize the tanks.

Wxx3 said:

Two reasons:
Primarily if i have a fuel problem, let's say i see something in the filters, I immediately switch tank feeds, drain, change filter, then try to figure out what's going on. If i'm feeding from both tanks, how do i do that?

Secondly, my returns are not equal. For whatever reason, if both returns are open, it will put most fuel in stbd tank, running the port tank dry.

And related to both issues, if you hande a problem in one tank and your feeding from and returning to both, you now have contaminated the good tank.

Unless, i'm crossing an ocean, I also only fill one tank at a time from the same source. Then, once in the tank, I'll run the fuel polisher a bit and if ok, only then equalize the tanks.

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Running your gen. too? Maybe your gen returns to only one tank???

Wxx3 said:

Two reasons:
Primarily if i have a fuel problem, let's say i see something in the filters, I immediately switch tank feeds, drain, change filter, then try to figure out what's going on. If i'm feeding from both tanks, how do i do that?

Secondly, my returns are not equal. For whatever reason, if both returns are open, it will put most fuel in stbd tank, running the port tank dry.

And related to both issues, if you hande a problem in one tank and your feeding from and returning to both, you now have contaminated the good tank.

Unless, i'm crossing an ocean, I also only fill one tank at a time from the same source. Then, once in the tank, I'll run the fuel polisher a bit and if ok, only then equalize the tanks.

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Thanks Richard.