Airlock in fuel tank?

[Severnman]

I decided to clean glass bowl of CAV filter because I had noticed on removing drain plug there was no fuel passing. The bowl was noted not to have much at all in the way of sludge. The filter element (replaced last April) was in apparent good condition. After refitting same I was unable to bleed the filter at all. Filter is well beneath tank level. Drifting filter again, opening fuel cock and nothing pouring through. Question. Do I have a blockage? Possible of course but filter element did not point to sludge build up. Tank is plastic 25 litre. Another thought - is it possibly an air lock since the feed pipe is attached to the top of the tank and presumably thence to vertical pipe with filter close to bottom? Tank is 7/8 full. Would filling tank to near deck level overcome this? Can fuel be sucked without ending up with a gobful of diesel. Anyone with similar experiences - answer on a postcard please. Engine is Yanmar 1GM. Thanks

 

[sailorman]

pressurise the tank with a dinghy pump with a cloth around the filler to seal it.
get a helper to pressurise you do the bleeding

 

[Cloven]

This may be a red herring but I did this job at the end of last season and it took a very long time to refill the CAV water separator ( it does not have a filter) and then bleed the rest of the system using the fuel pump lever. So long that at one point I also thought I had a problem. However, as mine does not have the filter I was at least able to see fuel slowly entering the glass bowl soon after I started pumping so I knew something was happening. It may be that it is just taking a long time for the filter to absorb the fresh fuel and then get into the glass bowl.

 

[sailorman]

if poss part fill the filter bowl proir to fitting.
i do the same if i can to oil filters

 

[VicS]

You have got to start it syphoning. Pressurising the tank as described is one possibility. Sucking is another but watch carefully and stop as soon as you see it reach the glass bowl or you will get a mouthful even so not a wise thing to do!

The lift pump may suck it through. If not a possible mod would be to fit an outboard engine type of rubber bulb to prime the system (My Peugeot car has one!)

 

[johnalison]

I don't know the Yanmar but with my Volvo the lift pump only works at a marked position (unlike my old motor which would pump at every other position except one).

 

[steve28]

I also prime the oil filter by running the engine on starter with the decompression levers up, until the oil light goes off. then i start up as normal. I wonder how many others do this type of thing.

steve

 

[pvb]

[ QUOTE ]
....it took a very long time to refill the CAV water separator.... using the fuel pump lever.

[/ QUOTE ]The fuel pump is cam operated. If the engine has stopped with the cam in a position where it's operating the fuel pump, then pressing the little lever won't have much effect. The answer is to turn the crankshaft enough to get the cam away from the fuel pump mechanism. I use a socket wrench on the crankshaft pulley bolts to turn it.

 

[sailorman]

De-Compress /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[Martin_J]

I have a 1GM10 and a plastic fuel tank (situated higher than the filter) that has the fuel line connected at the top.
Like VicS says - it was starting the syphon that was needed when you have an empty glass filter.
Not sure about your glass filter - but mine had a third screw fitting at the top (one for fuel in, one to the engine and the third blocked off).
The dinghy pump (with hose connected to the pump suction inlet) fits the third one exactly and with half a turn cracked off, a few pumps on the pump and the siphon starts. The screw can then be tightened enough without removing the pump as soon as the bowl starts to fill. Cracking it off again fills the bowl further.

Once glass is full the engine lift pump can continue with the bleeding - remember though there's more bleed screws - including one by the lift pump.

 

[sailorman]

i have a Nanni 37hp
the tank is under the Stbd berth & has similar probs. i have fitted a cav pump before the bowl but its still difficult even trying to pump that + the engine lift pump manually

 

[omega2]

Make sure you replaced the rubber rings correctly, did you use new ones? when I do ours I build the unit in my hand then offer up to the housing, pick up the bolt and then spin the filter/bowl and base up, this centers the unit when up to the housing nip up on bolt. Old rubbers are difficult to to realign, change them if you have new ones. I reckon you are dragging air.

 

[Severnman]

Many thanks to all. Dont think I'm dragging air as with the fuel cock open and the filter adrift all I'm trying to achieve is flow out the pipe. Clearly there is a syphon issue so thanks to those with their suggestions, all taken onboard. Second year with the boat and last time eveything went swimmingly. Perhaps I had a good head on the tank that was way above the tank head obviating the problem. Thought this might be the case just didnt want to find myself emptying more than necessary from the tank if all went pear shaped!

 

[johnneale]

If you pressurise the tank as described, - you also have to block off the tank vent.

 

[NFCN]

I spent quite a long time last year trying to get the fuel to come into my water separator after having changed the fuel filters. My engine is a Thornycroft T90 with the water separator below the level of the fuel tank.

Having taken some excellent advice in this very forum I just pulled the stop pull out and turned the engine over a few times. The fuel started to pour in and I bled the rest of the fuel system as normal. Easy really. But I guess if there was a blockage further up this might not help...