[Alberg30] Diesels, Fuel and Air

[John Birch]

Have you checked the low pressure line? 

If there is a crack or pin hole it may suck air in and cause an air lock.

John

----- Original Message ----- 
  From: Mike Lehman 
  To: public-list at alberg30.org 
  Sent: Wednesday, July 17, 2002 2:12 PM
  Subject: [Alberg30] Diesels, Fuel and Air


  Ever since I installed my diesel about 6 years ago, I have had this re-occurring problem, so I thought I would ask for advice from the list. I find that, after running the engine for several hours, I get a buildup of air in the fuel lines and the engine starts to stall and run poorly. The problem is so frequent and predictable that I keep a 10mm box wrench hanging next to the engine so I can quickly open the bleed valve on the injector pump and bleed off the air, then it will run fine for several more hours. It generally coincides with a change in engine speed. This always happens at the worst possible times, such as entering Sandy Point State Park between the Bay Bridge and the rock jetty with a 1-1/2 knt current and 20 knts of cross-wind while single-handing the boat. It makes you a damn good sailor, keeps you alert and sometimes scares the s--- out of you. 

  I have check everything: replaced the fuel pump, rebuilt the new Racor 500, keep the filters clean, use biospore, removed and cleaned the tank, removed the screen from the pickup tube, checked for water and contamination and now I am running out of ideas. It must be a design problem! My tank is an aluminum 18 gallon saddle tank mounted outboard in the starboard sail locker. The lines are all USCG approved rubber fuel lines. The supply is at the forward part of the tank and provides excellent gravity feed to the engine below. Next in line is the Racor, then the on-engine filter then the electric lift pump and finally to the injector pump. This all seems fine and designed appropriately. The return line connects to the rear of the tank to a t-fitting which is shared by the vent line. Here's my current thought....since the engine only burns 1/2 gallon per hour and the fuel pump feeds much more than that, a lot of fuel is being returned to the tank. Is it possible that the ret! urned fuel is blocking the vent thereby creating a vacuum causing the pump to suck harder and drawing in air from an otherwise air tight system? My thought is to convert the vent/return connection and make it "vent only". Then "T" the return line into the supply line between the tank and the Racor filter on the suction side of the pump.

  Does anyone have any thoughts on this?

  Mike Lehman 

  "Gilleleje" #505 
  "One can never enter the same river twice. The river is always new; the man is forever changed."



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