Fuel system bleeding - replace washers?

[robertsapp]

I'm bleeding the fuel system on my 3GM30F for the first time following replacement of the primary fuel filter. I imagine like most people experiencing this for the first time, I'm having a bit of trouble getting the engine to start again. I've read the very helpful post on fuel system bleeding (don't touch the 10mm screw!) but I have a question. Do any of the bleed screws use replaceable crush washers that should be replaced while bleeding? Neither the shop manual nor any of the posts I've read address this.

 

[Alan]

Robert, the bleed screw should already have a washer on it. When using a bleed screw the screw is not removed. You simply loosen it a turn or two and then re-tighten (not over tighten) when finished. To save yourself the hassle of bleeding ever again you can install a small electric fuel pump in place of the mechanical monster mounted on the side of the engine. By bypassing the mechanical pump you eliminate the possible diaphragm failure leak that would fill the crankcase with diesel oil and the ever present external leak on the pump.

 

[John T1594]

On the 3GM30F, there are two points at which you have to bleed trapped air after changing the engine fuel filter. The first is the "bleed screw" on top of the fuel filter housing. As described above, it should be loosened a few turns, then pump the fuel pump until clear and bubble free fuel flows out. You will have to pump a lot if you did not fill the filter housing with clean fuel before re-installing it. The screw has a fiber or plastic washer which should be inspected for cracks. The second bleed point is just forward of the filter assembly, on the top/side of the injector pump. It is also a 10 mm screw and located just under the rubber hose that feeds cooling water to the heat exchanger. I loosen mine with a 10mm socket on a short extention and then purge the air using the fuel pump lever. If you have not bled both of these points and still have trouble starting the engine, you may have air between the injector pump and the injectors. This will necessitate cracking the nuts on the lines feeding the injectors and then pumping fuel until the air has been cleared.
You do not say if you have a Racor (primary) filter on the fuel line before the engine. If so, that must be bled of air before bleeding the engine fliter (secondary) and injector pump.
I find it helpful to turn off the fuel supply from the tank when changing filters so fuel does not run into the bilge. I also use lots of Pampers under the filter bodies to absorb what fuel that does flow and spill.

 

[robertsapp]

I was changing the element in my Racor 110A primary filter. Engine RPM started dropping during last underway, and a quick email to the previous owner revealed the filter hadn't been changed in at least four years. I shut the fuel supply valve at the tank, replaced the filter element (it was black with crud), and bled the filter. Started engine, ran fine for 10 minutes, then coughed and died. Obviously air in the system. Bled primary again, bled secondary using the 12mm cap bolt (other posts advise leaving the 10mm bleed screw alone in order not to strip threads). Engine won't start. I spent 30 minutes looking for the injector pump bleed screw, and finally gave up. I didn't have my shop manual on board, a quick check when I returned home told me that injector pump bleed screw is in the center of the fuel line banjo fitting. No wonder I couldn't find it! So next chance I get, I'll bleed both filters again, then the injector pump, and see if she starts. If not, then I'll crack my injector lines and bleed there. I was just wondering if there were any washers that needed to be replaced as part of this process, so that I won't be chasing endless air leaks. Once it's running, then I'll change the engine (secondary) filter element. Why do it in two stages? This boat is a floating classroom for us, and I learn through repetition. When I finally get it running after changing the primary, and then go through all the steps again after changing the secondary, then I think I'll have it down in case I ever need to do it in a seaway.

 

[robertsapp]

Oh, and I did remember to reopen the fuel supply valve.

 

[Steve Dion]

I have never had to open the bleed screw on the injectors. Only the one on the secondary filter (small one on the engine). I have often used the starter to bleed the system. Just pull the engine fuel shut off, close the raw water intake (you don't want to flood the engine with water). Have someone crank the key with the 10mm secondary bolt slightly open. It will start spirting fuel and you can start closing it as it attempts to start. It may take a couple of tries.

It is also good to fill your primary filter before you start this process. If you have changed the secondary Yanmar filter, you should try filling that bowl with fuel too.

Where did you information about NOT using the 10mm bolt on the secondary filter to bleed?

 

[Dan Johnson]

Robert...

when I redid my fuel system I replaced ALL the washers. They're cheap and ensured that an ill-fitting one wasn't leaking air. The plastic one on the bleed screw atop the Yanmar filter is suspect as JohnT pointed out. Was a problem for me. I added a squeeze bulb between my Racor and the lift pump to aid the bleeding process as the lift pump lever isn't the easiest to work. As suggested, an electric fuel pump there would do the same thing. Once you've found the air leak, the 3GM will run forever.

 

[robertsapp]

Re: Robert...

The advice on leaving the 10mm bleed screw alone came from an excellent article with pictures on bleeding the fuel system I found by searching the forum. I stopped by my local friendly Yanmar parts dealer yesterday after work, and while he hadn't heard that particular advice before, he did admit that he has to order a lot of filter assemblies for people who have overtightened that particular screw and have stripped the threads. Yanmar apparantly won't sell just the head unit, you have to purchase the entire filter assembly. Anyway, while I was there we broke out all the little packages of various washers, and he fixed me up with a 'washer kit' to replace all the washers under my various bleed screws. Turns out the 12mm bolt that I used to bleed the secondary filter uses a copper washer that isn't really crushable, but is subject to work hardening and gets difficult to seal after a few uses. Another great tip I've picked up in this process is to use a plastic syringe to fill the fuel filter through the bleed screw hole rather then attempt to pour fuel into the bowl before installing.