Diesel Leak of fuel pump

[agroman]

I have got a diesel leak from the bottom of my pump. It was serviced by Peter Strong last winter and has been dry until recently. It is a drip that increases with engine speed. It appears t be coming from a threaded hole in the very bottom of the pump. See the picture. Not sure if there should be something screwed into the hole or if there is a seal at the bottom of the threads - its difficult to see!

Any ideas?

[Jerry Coles]

That's where there is normally a tube with a 360 deg loop in it goes. Mine does drip also but when your driving you don'y notice it.
Jerry

[agroman]

I guess it's a kind of breather then. Funny I have noticed a pipe like this one some pumps now you mention it. Don't remember there being one on mine though when I stripped it down last year? Also strange I have not noticed it dripping until now. I think the thread is 1/2" 20tpi?. I will get a male pipe nut and some 6mm copper pipe, make a bubble flare end and raise the tube up to about half way up the pump and put a pig tail in the pipe, does this sound about right?

Originally would the pipe be on the outside / inside or rear of the pump?

[agroman]

Do others have this pipe with a pig tail in it fitted to their pumps?

[russelm]

They should all have it and there should be a 360 degree loop to stop crud getting in (this fills with diesel like a U bend)

You can see it in this photo (this is a lot currently on ebay)

[agroman]

Thanks
This pipe looks as it would point directly down from the bottom of the pump. Would the loop be enough to stop diesel leaking out.
Talking to Peter Strong he suggested bringing a similar pipe upwards with the opening about half way up the pump body.

[russelm]

The whole basis of the setup is to allow diesel to leak out in a controlled manner, the end of the pipe actually should pass through a small bracket which is attached to one of the sump bolts.

The loop acts as a trap to stop gunk and foreign bodies getting in.

The alternative of bringing a pipe up the side of the pump does not, to me, seem well considered because:

1) It means diesel would run down the pipe and drip off the bend at the base then down the side of your block and off the sump.
2) Would allow crud and rain to physically fall in under gravity.

The whole setup is there because the internal diesel pump pistons will suffer some leaking of diesel, this diesel ultimately lubricates the pump and when there is to much, must be handled and removed (to stop pressure building up). Many more modern pumps actually have a return pipe to the tank (a possible option if you fancy some extra plumbing?)

[agroman]

Might mine be leaking out more diesel than it should then?

On tick over there is nothing, but if I rev the engine I get a constant dripping.
Does this point to seals in the pump?
I hope not as it was overhauled back in the winter so probably not done more than 50 or so hours since rebuild.

If you plumbed the pipe back to the tank you would have to raise it up, this might cause a problem with raising the diesel level in the pump too much and creating pressure?

I guess the idea of raising the pipe un to half way up the pump stops fuel from leaking out by increasing the depth and there fore pressure so that less leaks pass the seals? Not sure As I have never had one of these pumps apart.

[oldcharlie]

Mine pores fuel from more than one place, I know it needs to be rebuilt but that is quite expensive and hard to find someone to do here in the U.S.
I hope to get it built in the spring before summer work begins.

[russelm]

The lubricating fuel depth is already set by a dip tube in the pump so raising the level wont give any benefit plus, the fuel pressure in the pumps pistons will be a few hundred psi which will easily overcome a fraction of a psi of head.

Thinking again about a return to the tank, for these pumps it may not work as the fuel pump has a vent (filter) on it.

I would expect there to be some leak off, not excessive and clearly more when loaded up (as the pistons are pressurised over a much longer portion of their stroke)