Air in Diesel Fuel System

[John A]

Air will acumulate in the Injector pump and creates an air lock. By opening a bleeder value on the injector pump and forceing fuel into the injector pump you force this air bubble out of the injector pump through this valve. There can be no air within the injector pump for fuel to flow.

You may have a leak befor the electric pump.

[Nemo55]

Once air is bled from the system once, then that's it!! you shouldn't have any other issues with air unless it is constantly getting re-introduced to the system yet again.
If you are...then you most definitely have a hole someplace letting it in.
Start at the most logical place and go through the system stage by stage until you isolate the weak link, then repair or replace. Caution though....make sure any materials you use are diesel fuel compatible, because diesel will eat and melt quite alot of non compatible parts,,like cheap replacement hose,,or "Strainer" material. G'Luck to ya!!

[YACHT TARENTELA]

I was going crazy trying to figure out the cause of my engine quitting. All the "experts" and "professionals" alike gave me such a number of reasons I cant list them all. I finally discovered air bubbles showing through my glass bowl racor and traced the problem back to my fuel pickup tube. With 30 gal. diesel in my 100 gal tank there is sufficient sloshing around in a moderate seaway to allow enough air into the system to starve the motor and cause it to quit. I have a primer bulb which when pumped forces the air out ( through the fuel return line I think) and the engine runs properly until more air is sucked in due to the sloshing of the fuel in the tank. Now all I have to do is figure out how to remove the pickup line and extend it closer to the bottom of the tank. In the meantime I keep enough fuel in the tank to keep this problem from occuring.

[gonesail]

test fuel line from tank to lift pump. if rubber hose then check all clamps and look for any fuel leakage .. if hose if old replace it and make sure it is the right diameter for the fittings. check banjo fittings and copper washers. if getting air in pickup tube then not sure what you can do besides keeping more fuel in the tank.

[Nemo55]

Also remember that Diesel is a high suspension fluid,,meaning: if you agitate and aerate the fuel,,it will take a while before it releases all the air bubbles.
which is why its always a toss up whether to pick the fuel up from the bottom of the filter(no air but chance of water) or from the top (No Water but a chance of air.
At least if you follow the rule of filling when your tank reaches half way empty then you should never have to come this way again.

Originally Posted by YACHT TARENTELA

I was going crazy trying to figure out the cause of my engine quitting. All the "experts" and "professionals" alike gave me such a number of reasons I cant list them all. I finally discovered air bubbles showing through my glass bowl racor and traced the problem back to my fuel pickup tube. With 30 gal. diesel in my 100 gal tank there is sufficient sloshing around in a moderate seaway to allow enough air into the system to starve the motor and cause it to quit. I have a primer bulb which when pumped forces the air out ( through the fuel return line I think) and the engine runs properly until more air is sucked in due to the sloshing of the fuel in the tank. Now all I have to do is figure out how to remove the pickup line and extend it closer to the bottom of the tank. In the meantime I keep enough fuel in the tank to keep this problem from occuring.

[epistosaurus]

Originally Posted by tallyhorob

you don't need to bypass the lift pump, most electoral fuel pumps are add in line to "prime, bleed" the system and can act as a back up if the lift pump fails.

I just bought a small electric fuel pump which I want to put between my Racor and the engines lift pump on my Perkins. My question is can I install it inline? or do I need to make a bypass line with the valve. The pump will be used only for bleeding.

I am asking since I thought that during normal engine operation, the lift pump will need to pump the fuel through the (shut down) electrical pump and I am not sure whether this will work? That is why I initially thought about putting it in parallel but maybe it does not need to be that complicated...


I had quite a number of problems with my Perkins last season shutting down at the most inopportune moments which we eventually traced to blocked pickup tube in the tank. The funny thing is I spent $100 on a professional tank cleaner prior to commisioning the new (to me) boat but it turned out that was not enough. What my mechanic told me (too late!) was that the tank was initially used with gasoline (original engine on that boat was apparently A4) and when they converted to diesel they did not clean the tank properly. Apparently when you start using diesel in previous gas tank a hard shellac develops which is very hard to get rid off. We started having problems after a nice 10h passage in moderate seaway - probably enough to shake some of that shellac off and block the tube.

thanks!