Willy Lewis

Brewer South Freeport Marine, ME

The injection pump on a diesel engine is great for pumping fuel, but when air gets into the fuel system—from changing fuel filters, for example—you have to bleed it out. Fill the primary fuel filters with clean diesel. You can also draw fuel into them using the hand pump, but that will take at least five minutes of pumping. Better to prime them. Find the bleeders, crack them open, use the hand pump until solid fuel comes out, and then close them. If the engine hasn’t been run dry, it will probably start. If the engine ran out of fuel, then on an old-fashioned diesel, you’ll have to bleed the injectors, too. Using an open-end wrench, crack the fuel supply lines at each injector about half a turn. Crank the engine, and tighten each fuel line when you see solid fuel. The engine should fire.

Bill Cripps

Mystic Shipyard, Mystic, CT

A common-rail diesel usually doesn’t need bleeding. You can often just crank it until it starts. But it’s easier, when you’re changing fuel filters or if the engine’s been run dry, to fill the primary filters from a container. Then, use the hand pump on the diesel engine to move the fuel into the secondary filter. This is a plunger-style pump: You simply unscrew the collar and pull out the plunger. Don’t open the secondary filter, but fill it by pumping. Once you feel firm pressure against the plunger, re-stow it and then start the engine. Any air left in the lines will be blown through. Never loosen a fuel line on a common-rail diesel; there’s enough pressure to take off some skin with fuel spraying out. If you do open a line, you have to throw it away and replace it with a new one. 

Don Young

Dutch Wharf Boat Yard, Branford, CT

You can get air in the lines in many ways: A valve can have a bad seal; O-rings can be worn; hoses can be in bad shape. If your engine stops, check the filters: They have to be chock-a-block full. If they’re not, you’ve got air. With older diesels, you had to get all the air out, but a common-rail engine, with its high fuel pressure, will almost bleed itself. You don’t have to crack the injectors open like on the older engines, and you shouldn’t; the fuel pressure is enough to cut you if the spray hits you. Don’t do anything beyond the secondary fuel filter, the one on the engine. Many engines have a bleed point on that filter; that’s as far as you should go. Crack the bleeder, use the hand lift pump to fill the filter until solid fuel comes out, and then close the bleeder and start the engine. 

This article originally appeared in the March 2020 issue.



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