Bleeding air in fuel!

[lw395]

I think you are right, the CAV filter is prime suspect, but it ought to be fairly easy to sort.
You could try unbolting it from the bulkhead or whatever and temporarily lowering it to below the fuel level in the tank. If that does not cure it, suspect either the lift pump, or the tank fitting.
While you are at it, check the tank breather, if that's blocked the negative pressure will be a much bigger problem.
Also check there is plenty of fuel in the tank, some tanks draw from a long way above the bottom and occasionally draw in air due to vibration/heeling/aeration of the fuel from the return.
Check that none of the joints are under stress from pipes bent through small radii etc.

 

[bendyone]

Had the same on my Lister, 2 hours running and air would build up in the secondary filter. This year I have replace all the pipes and primary filter so fingers crossed.
If it was a fuel leaking easy to find but air getting in is hard.

 

[A1Sailor]

It may or may not be relevant - but is your tank OK?
I had problems with air appearing in the engine fuel filter (not the fuel/water separator) which I bled & bled & bled & bled - then bled again! When I eventually looked, I discovered that the bottom of my tank was full of:

and when I cleaned it out:

the air stopped appearing and the engine was happy again

Presumably the fuel lift pump was generating such negative pressure that when the fuel uplift pipe in the tank got blocked with ***** it was able to draw air in - even through seemingly tight connections.

As I said - it may or may not be relevant. Good luck identifying the problem.

 

[KellysEye]

Diesel willl go through a microscopic hole i.e one you can't see. One way to test a weld is to put talcum powder (or equivalent) on one side of the weld and paint diesel on the other, if there is even the tiniest hole then the diesel will wet the powder. I'd suggest you put talcum powder on the lift pump. If it no diesel appears it isn't leaking and it's another problem. By the way make sure the pump is dry before you start.

 

[Poignard]

I would disconnect the line at the tank, block it off and then connect the priming bulb to the pipe feeding the lift pump so you can pressurise the line between the tank outlet and the lift pump inlet. You can then look to air or fuel leaking from the connections in the line.

That's the way to go. If air can get sucked in it can also get blown out, and it's easier to trace where air is leaking out.

 

[Caer Urfa]

Is there an easy way of locating a tiny tiny leak in the suction side of my lift pump?
My 1GM10 will run happily for 39 - 40 minutes before spluttering to a halt. Bleed the system and away she goes again; quite happy.
I've put a priming bulb between dip tube and filter. Every 15 minutes or so I dive below, squeeze the bulb a few times until it goes 'hard', and the engine will run forever. (I thought the bulb might be the problem. It isn't, but it is a temporary fix).
Wherever the air is getting in it must be the tiniest of holes as even by squeezing the bulb really hard I cannot find a fuel weep.

Any ideas?

Not sure without seeing your system but 'maybe' the answer lies elsewhere.

About five years ago after refitting an all new fuel system the engine would run for six hours no problem then just stop. Bleed the system and it would run another six hours then stop and so on.

You name it I changed it and spents weeks trying to find an air diesel leak until someone said the new primary filters 'looked' to be fitted too high in relation to the fuel tanks bottom, I repostioned them by lowering them so they are always 'gravity fed', never had a problem since so might be worth checking.

Mike
Control side of twin tank system.

Each tank has it's own filter

 

[ianabc]

Pressure helps...

Many marine owners fit an outboard primer bulb to the diesel fuel hose as this allows you to rapidly pump diesel and quickly prime and pressurize the system allowing one to find leaks!

 

[Porthandbuoy]

Is there an easy way of locating a tiny tiny leak in the suction side of my lift pump?
My 1GM10 will run happily for 39 - 40 minutes before spluttering to a halt. Bleed the system and away she goes again; quite happy.
I've put a priming bulb between dip tube and filter. Every 15 minutes or so I dive below, squeeze the bulb a few times until it goes 'hard', and the engine will run forever. (I thought the bulb might be the problem. It isn't, but it is a temporary fix).
Wherever the air is getting in it must be the tiniest of holes as even by squeezing the bulb really hard I cannot find a fuel weep.

Any ideas?

I think I may have cracked it!

After cleaning every joint on the suction side of the lift pump thoroughly I dusted each joint with talc as advised. I then squeezed the priming bulb hard, and kept it squeezed. Eventually, and it took a while, the talc around the bleed screw on top of the CAV filter wetted out. Bingo!

Changed the copper washer for a fibre one, repeated the test, no sign of a leak. All the other joints stayed dry.

Ran the engine for an hour without a problem.

Thanks everyone for their advice and tips.

 

[KellysEye]

>I dusted each joint with talc as advised... Bingo!

I'm glad that worked I don't think many people know that you can do that to test for tiny diesel leaks. Hopefully word will spread.

 

[oldvarnish]

Thanks for posting that. One more v useful trick learned.

 

[snooks]

I think I may have cracked it!

After cleaning every joint on the suction side of the lift pump thoroughly I dusted each joint with talc as advised. I then squeezed the priming bulb hard, and kept it squeezed. Eventually, and it took a while, the talc around the bleed screw on top of the CAV filter wetted out. Bingo!

Changed the copper washer for a fibre one, repeated the test, no sign of a leak. All the other joints stayed dry.

[smug] Told you so in post #4 [/smug]

Glad you got it sorted