Why does my diesel engine keep dying?

[LifePart2]

I have the usual arrangement - fuel tank, then copper pipe to Racor filter, then rubber hose to mechanical fuel pump, another rubber hose to the second filter, and a final rubber hose to the injection pump. The filters are both new and clean. The valve on the tank is open. I have new o-rings on the lid for the Racor.

Over the summer I had the fuel tank taken out to have a leak repaired. Since then I have been having the following problem:

The engine starts fine. Then after about 10 minutes it runs out of fuel and dies. I know this because if I open up the racor filter, the fuel level is down to the level of the outlet hose. I top it up with fresh fuel and then, after a bit of self-bleeding, the engine starts and runs fine for another 10 minutes.

My diagnosis is that we are somehow getting air sucked in to the pipe that leads into the Racor. I am presuming the leak is before the Racor and not after it as it is the Racor that is filling with air while the fuel is being sucked out to fuel pump. The fuel pump would seem to be functioning fine.

Is that a correct diagnosis? Or am I missing something?

If it is correct, then the next question is where is that air getting in to the system. The obvious suspect is the connection between the copper pipe and the valve on the tank, since that is what was disconnected when the tank was removed.

I have removed that connection twice, and applied some sticky blue sealant that is meant for fuel and gas lines. But, alas, it has not remedied the problem.

So, how do I find where the air is getting in? There are no fuel drips that I can see anywhere.

And how do I seal it? I am still, I guess, suspecting the pipe to valve connection. Is there some other sealant I can smother the joint with to ensure it is air tight? Or, again, am I missing something? For good measure I could also smother the valve to tank joint (which was not disturbed) and maybe the copper pipe to Racor connection, which was also not disturbed?

Or could there be some pinhole in the copper pipe? How would I find that?

Any suggestions would be very gratefully received!

Thanks in advance,

Noel

[Kalinka1]

It could be the o ring seal on the racor filter. I had the same thing happen after a mechanic replaced the secondary fuel filter with a different make. The rubber gasket turned out to be a harder rubber and wouldn't seal. I reused the old filter and seal and it has been running fine ever since.

[DeepFrz]

Check the pick up tube in the fuel tank. It sounds like you are just running on the fuel that you supply to the filter and not getting anything from the tank.

[moctrams]

I've seen where people forgot to take out old Racor o-ring and installed a new one along with the old one. One time an owner reversed the in/out on Racor.

[knot smart]

My vote would be to disconnect the fuel line at the pick up line at the fuel tank and plug it up. Then disconnect the fuel line at the motor and then pressurize it with fuel. Follow The Line back and see where it's squirting. I would take the fuel tank from my dinghy outboard, dump out the gas, put some diesel in it and use the squeeze bulb to pressurize the line. The critical part about this plan is to make sure that you get all of the gas out of the squeeze bulb and the tank before putting a gallon of diesel in it.

Doesn't the Racor filter half a bleeder valve at the top of it? Before I do anything I'd make sure that bleeder valve is closed tightly. Now that I think about it that may be the culprit right there

[j.g.evans]

My diesel kept dying and restarting after stopping. My problem was rust flakes from the iron tank that would plug the pick up tube and then fall away when the engine stopped.

[DeepFrz]

Just a thought but did you fill the tank after it was repaired?

[NYSail]

Never saw copper tube in the fuel lines...... only have seen rubber hose. But I do second pulling the fuel pick up. If there is a screen remove it. Also as was said check all your gaskets in the racor.

Good luck

[Exctyengr]

You might also have a vent problem. To check, try opening the fill pipe and then running the engine. If it keeps running check the vent It might be plugged (insects sometimes nest in them). The vent is usually a small chrome fitting on the hull just below the fill pipe.

[kenbo]

Good ideas above, I think you're on the right track thinking the issue is a vacuum leak including the primary filter back to the bottom of the fill tube in the tank.

Pull a vacuum using a squeeze bulb on the tank valve outlet. Put the outlet tube in a container with diesel, any bubbles?

You don't say what type of mechanical connection where the copper tubing attached to the tank valve. If it's a flare connection you should be OK. But if it's a compression fitting I'd be suspect. Test with that bucket of diesel again. This time connect the outlet of the bulb to the copper tube, close the tank valve and pressurize, if there's a leak you'll find it.
Lastly, check the filter fit again for single o- ring and proper installation.
Good luck!

[Russ]

Knot smart has the Correct answer. I’ve been there painfully trying to find an air leak. Since the engine sucks fuel you may not get a fuel drip unless you pressurize the entire system I used a small vdc pump to do it. I connected the pump to the fuel line where it exits the fuel tank. A neat trick is to wrap a small piece of paper towel around very fitting. Then you will see the telltale diesel fuel in the paper at the leak point. . Saves missing a slow drip.

[beirutsailor]

Glad you found the fault. Otherwise it sounded like an overdue-for-change secondary fuel filter. Had this twic !

[Scorpius]

Since you have pulled and replaced the tank, I would start there. Assuming your tank outlet is at the top (where it should be) the air leak is very possibly there - either side of the valve. Another possibility is that, when the tank was pulled, then replaced, the copper pipe was flexed and cracked.

I have a tank down at the bottom of the keel with a lift approaching five feet. I was concerned it would be too much for the mechanical pump on the engine so I installed an electric pump down close to the tank. Although it turned out to be unnecessary for the original purpose, it has turned out to be a godsend for diagnosing fuel problems and bleeding the engine when necessary. With the electric pump on, the whole fuel system downstream of it is pressurized and leaks are obvious. For bleeding, just turn the pump on, crack the bleed screws until they run clear, re-tighten and voila, you're done! Ten seconds tops. The longest part of the job is finding the right wrench for the bleed screws!

[rocnrichy]

I had the same problem with my engine stalling 20 minutes after start up. Drove me nuts til i pulled the puck up tube and found it was a steel pipe that was completely perforated with tiny holes. it's worth checking out.

[Q Xopa]

Originally Posted by Scorpius

Since you have pulled and replaced the tank, I would start there. Assuming your tank outlet is at the top (where it should be) the air leak is very possibly there - either side of the valve. Another possibility is that, when the tank was pulled, then replaced, the copper pipe was flexed and cracked.

I have a tank down at the bottom of the keel with a lift approaching five feet. I was concerned it would be too much for the mechanical pump on the engine so I installed an electric pump down close to the tank. Although it turned out to be unnecessary for the original purpose, it has turned out to be a godsend for diagnosing fuel problems and bleeding the engine when necessary. With the electric pump on, the whole fuel system downstream of it is pressurized and leaks are obvious. For bleeding, just turn the pump on, crack the bleed screws until they run clear, re-tighten and voila, you're done! Ten seconds tops. The longest part of the job is finding the right wrench for the bleed screws!

This reminds me of recent discussions about integrated fuel polishing systems. Ie an extra pump and filter loop.

With a couple of valves this can also pressurise your fuel system to make bleeding and finding leaks a lot easier.

Just a thought.