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Priming a Diesel Fuel System

3K views 13 replies 7 participants last post by  SloopJonB 
#1 ·
I'm in a new (for me) situation and need some advice. I had to pull my Racor filter housing out to disassemble and clean it. Every other boat I've owned had the fuel line exit the bottom of the tank so the system would fill when the petcock was opened - just had to crack the top of the Racor until fuel dribbled out the top.. The fuel line in this boat comes out of the top of the tank so the Racor doesn't automatically fill when I open the petcock.



What is the usual procedure for priming the system in this situation? Do I have to put a draw pump on the Racor bowl drain and get a siphon going or what?
 
#2 ·
I had started a thread not too long ago titled "Where did the air go" or something close to that.
Anyway I had replaced the line from the filter to the tank. I didn't bleed the system, didn't prefill
the new line, engine started up and has now ran fine for three hours. Some of the explanations
were self bleeding, a little air will work itself out and I got lucky. If it was my filter bowl, I'd fill it
with clean diesel, button it up and start the engine. And my fuel line came off the top of the tank
with the filter above the top of the tank.
 
#3 ·
If the filter location is lower than the fuel level in the tank, you can simply wrap your lips around the filter outlet and suck. Stop when the liquid gets to you. Probably ,another way would be to have permanently installed pulse pump ,either with bypass valveing or as main run all the time fuel pump .With a little extra wiring and plumbing could also feed a diesel fireplace Keep the tank full
 
#4 ·
I am not sure where you are in the process but the advice given me was to close the fuel valve on the tank so the fuel in the line can't flow back before you remove the filter. Use a small funnel and fill the new filter as far as you can (which was not very much) and then put the filter on. Once it's on use the lift pump on the engine to bleed the system at least as far as the engine mounted filter.

If you have never done this before, and you have a cam driven lift pump, it helps to put one finger on the pump lever and then turn the crankshaft with your other hand until you feel the pump has a full stroke. It greatly reduces the number of stokes.

Jeff
 
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#5 · (Edited)
What rich said! Another thing to look at is the check valve at the Tank most have a simple spring ball check as a siphon break if the filter and/or Motor is below the fuel Tank. When I prime mine (with the lever on the mechanical pump) I can hear the air and fuel squishing through the check valve. On a system that returns a lot of fuel it becomes less critical to prime but I always do.

Sorry credit to Jeff...
 
#6 ·
I got'er done - put a small draw pump on the outlet of the Racor and sucked it sort of full (above the inlet/outlet level) then cracked the bleeder on the engine filter and used the tickler on the engine pump until the filter stopped bubbling.



Now I'm back where I started with a diesel that won't start but now it has a clean fuel system.
 
#7 ·
On a gas engine when it won't start its one of two main things, no gas or no spark.
On diesels?? no fuel, no to low compression, maybe timing of injection off?
Can a blocked exhaust keep it from starting?
On a small gas engine I will spray some flammable substance (starting fluid) to see if it start.
If it does then I know its a fuel situation.
Does the engine have glow plugs?
 
#8 ·
You may need to bleed the Injectors also. Lots of fuel goes around the high pressure pump back to the Tank, but an air pocket in the line to the Injector will prevent starting.
All the stuff meme suggests are real things but I doubt any of them are the culprit. You can start by throwing the compression release to get a good spin(if you have one) this may clear it out. If not crack the tube directly on the Injector one at a time. Don't try too long without closing the water inlet so you don't hydro-lock.
 
#9 ·
It's a Yannie 2GMF. It motored over here from Saanich - about 8 hours with no problems. Fired right up the next day to move to the hoist and then sat on the hard for several weeks while I did the bottom. Fired right up on launch and ran fine while moving to my berth. Sat again for a couple of weeks while I sorted the running rigging and some other things. Then I went to start it to warm the oil before changing it and it wouldn't start.

I've had the raw intake closed ever since I realized it was cranking too much.

It cranks fine with the CR closed and spins faster with it open so I can't see a sudden loss of compression.

Nothing happened to get air in the lines while it sat in the berth.

The filters needed servicing but weren't plugged or full of water.

I'm baffled. Time to get a pro in I guess (lots of luck at this time of year).
 
#12 ·
It's a pull knob in the cockpit but I checked it at the engine and it's off.
 
#11 ·
I suggest backing a high pressure injector line nut off about 1 turn, and hitting the starter again. If fuel leaks out of the injector line, you know that the problem is the injector, or compression in the cylinder.
 
#13 ·
Have had same problem with my 2 GMF. Filled both Racor and secondary filter on engine with diesel. Engine would start and you bleed through the bleed screw on secondary filter. Engine would run until fuel in bowls ran out. The mechanical fuel pump on the Yanmar doesn't have enough power to pull fuel out of tank to the Racor filter if their is air in the line especially if the tank outlet is at or slightly below fuel filter.Most annoying problem. I tried blowing air in fuel line with my mouth and could hear bubbling in the tank so I knew it wasn't a defective shut off valve of clogged pick up in the tank.

The fix. This only happens if you run the system completely dry like when the Racor is completely clogged. Typically you are running the engine at about 2600 rpm it does a slow reduction in RPM and then shuts off completely. Oh yeah the fix. I put an outboard engine primer bulb in the fuel line between the engine and the tank. Replace the filters, and then pump it which pressurizes the system and pulls fuel out of the tank. Bleed the line after it starts running. It worked for me.
 
#14 ·
It's alive!

Cracking the injectors and spinning it a bit with the CR released did the trick. My guy found some other things while he was head down in the engine so it was money well spent.

Still no idea why it originally decided to stop lighting up - it just sat for a week or so after the last time it ran so.....

Oil change tomorrow and I'm done.
 
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