Fuel leak, Yanmar 1GM10

[tilmansailing]

My fuel system has developed a leak, pumped about 25 litres of diesel into the bilge over about 8 hours running. When the engine is NOT running - no leak.
I have checked the water separator filter and the engine fuel filter for leaks, nothing significant.
I can see no fuel dripping from the engine while it is running.
While the engine IS running the rpm (a) does not respond normally to throttle action, at times I only get just over 2000 rpm but it occasionally rises to 2750rpm without any throttle movement.
I am home until 14th July, the boat is in France (St Martin, Ile de Re). When I return to the boat it will be Bastille day (big public holiday) so no marine engineer to consult right away on my return.
I am at a loss as to what to investigate next - any suggestions would be welcome.
Or, would someone advise me how to explain all this in French, to an engineer whose English is probably no better than my French?

 

[vyv_cox]

pumped about 25 litres of diesel into the bilge over about 8 hours running.

Sorry, but you are just not looking carefully enough. At that rate you are losing 3 litres per hour, that's 50 ml per minute! You need to run the engine for a while and inspect it carefully, it must soon be very obvious where a leak that big is coming from.

It can't be the separator as that is under constant head whether engine running or not (assuming you mean a primary filter). Something after the lift pump sounds most likely, either the pump itself or the secondary filter. Maybe injector pipe loose.

 

[earlybird]

Could it be the spill return line back to the tank? although the speed variation might suggest not.

 

[steve28]

have you checked the sump and engine isnt full of fuel, not likeley but has been know due to lift pump diaphram failure.

Steve

 

[smth448]

I had a similar problem with my 1GM10 and it was due to one of the fuel lines shaking loose. Check the fuel system from end to end for any loose connections. Also check the engine for leaks when under load. Your leak will probebly be after the lift pump and will only be evident when the engine is under load.

 

[wiggy]

My advice would be to clean engine and all lines/unions carefully then cover in talcum powder. Run the engine for a short while and leaks will show more easily. If no wet aqreas found could it be where the fuel return enters the tank?

 

[25931]

When we had the same symptoms we found that the fuel filter bowl was not tight enough.

 

[Heckler]

Sorry, but you are just not looking carefully enough. At that rate you are losing 3 litres per hour, that's 50 ml per minute! You need to run the engine for a while and inspect it carefully, it must soon be very obvious where a leak that big is coming from.

It can't be the separator as that is under constant head whether engine running or not (assuming you mean a primary filter). Something after the lift pump sounds most likely, either the pump itself or the secondary filter. Maybe injector pipe loose.

Vyv
its got to be on the pressure side, although the varying revs suggest otherwise! Unless his description is out a bit, ie it hunts after startup when the air in the system is being got rid of thru the spill system.
I know I had a leak similar once but carefull obs soon spotted it coming from a spill pipe nut.
Stu

 

[tilmansailing]

I am sure you are correct regarding the pressure side. I have examined the engine whilst it is running (but not under load, as I am at the end of a raft) there are no visible drips from the engine. I am beginning to think that the leak is somewhere off to the side, up by the fuel tank area, then running down into the bilge. That would suggest the fuel return pipe?
As far as the varying rpm, that may be a separate problem although I have bled the system - no obvious air.
When I get back I will get the boat moved on to a catway (pontoon finger) where I can run it under load. Maybe then I will be able to see where the leak is?