Ford 851 diesel fuel leak

Eastgeboo · Feb 11, 2015

On the right side of my 851 diesel valve cover there is a round disk held on by a wing nut.
The last time I started it there was diesel fuel spraying out from under that disk. Should I suspect a leak in the excess fuel return line under the cover and if so, after I remove the cover, how do I test to see just where the leak is?
Another symptom...the crankcase is right on the full line, but it is straight diesel. I always shut off fuel valve after each use. How can I test to see it that needs to be replaced?
Thanks for any help!

john in la · Feb 11, 2015

Shutting off the fuel does no good for the return line.
If the stand pipe in your tank is good the return line will only leak when it is running. If the stand pipe is broken it will leak 24/7 threw the return line.

Take the valve cover off and you may see where it is leaking. If not a quick start up will show it if it is leaking bad enough to spray out the breather vent.

Eastgeboo · Feb 11, 2015

(quoted from post at 20:28:58 02/11/15) Shutting off the fuel does no good for the return line.
If the stand pipe in your tank is good the return line will only leak when it is running. If the stand pipe is broken it will leak 24/7 threw the return line.

Take the valve cover off and you may see where it is leaking. If not a quick start up will show it if it is leaking bad enough to spray out the breather vent.

Thanks. What would be your first guess if you had diesel spraying out of that breather vent?

john in la · Feb 11, 2015

The breather vent should have a wire mesh in it. For it to be spraying out the vent I would suspect the pressure side (fuel in line) to be leaking in just the right spot to spray on the vent.

With that said those return lines are known to leak at the joints but its more of a drip.
The stand pipes are also known to break off and be laying in the bottom of the fuel tank.
With a broken stand pipe and a dripping fuel return line you can fill the crankcase with diesel rather quickly even with the fuel shut off.
But this would not account for the spraying of fuel.

Another common spot for fuel leaks is the seals on the injector pump shaft. This will also fill the crank case but will not spray fuel out breather and is shut off when the fuel is turned off.

This is the reason I suspect the pressure side where the line bolts to the injector.
Get the valve cover off and have a look see. It is tight but you can get it off with the fuel tank in place.

Eastgeboo · Feb 11, 2015

I thank you very, very much for your detailed reply! I will have a look ASAP.

Ford 851 diesel fuel leak

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