Volvo MD 11C: I'm getting air in the fuel line, or maybe I'm pulling a vacuum. Either way, bleeding the fuel system is the quick fix, but problem reoccurs, usually several day-trips later totally 2-4 hours of engine time.

The problems doesn't appear to be related to engine speed or load. It lost fuel system prime while idling at the dock. This happened before, and now after, I changed all the filters (two CAVs, lift pump screen and main filter cartridge.) The only common thread is that the engine is at operating temperature when it happens.

All the fittings are snug. New O-rings on the lines comming off the high pressure pump. The main filter was assembled on the bench to ensure that the square O-ring didn't twist.

Two fuel tanks "T" together to feed the lift pump. Both fuel cutoffs are open. Bottom of tanks are higher than the engine, so even if the lift pump fails gravity feed should be enough (?). Fuel lines are about 5 years old.

Lift pump diaphragm is probably 50 engine-hours old, and the hand level provides plenty of pressure to bleed the system. However, the rubber hose, the one with the banjo fittings is probably 1977 vintage, but there is no evidence of diesel on the outside of the engine (leaks.)

Any ideas? 

How to I de-bug this problem??

Ed and Karen

CAPRICA #687

Like Mike, I have run into a situation where mud wasps had plugged up the overboard fuel tank vent.  Depending on how much fuel was in the tank the engine would run until it couldn't over come the vacuum of the sealed vent.  I had this happen a couple of times, it was a bugger to figure out at first ( no pun intended).  Now I poke a drill bit into the vent every few weeks just to be safe!  I was out on the hard last week for bottom paint and found both my fuel and holding tank vents filled with mud!

Kevin