3QM30 leaking fuel

[HUDSON]

Hi friends
I recently bought 84 37 "hunter and there is a fuel leak . I have had two mechanics look at it with no luck!
It doesn't seem to be fuel lines or tank and only leaks under power .
Any thoughts ?
Thanking you in advance
Hudson

 

[kloudie1]

Check the return line from the injectors to the tank.. No pressure in it but when the engine is running, a crack in the rubber line will leak.. On the QM, I think the return goes back to the secondary filter.. but I'd suspect that line and the fittings. I had that and it took a while to find it.. The hose was the original from 1985.
Otherwise any pressure fitting past the lift pump.. The banjo fittings at the lift pump, the secondary filter, and the HP pump are all suspects.. Use a clean tissue to touch the fittings when the engine is running and the one that wets the tissue is the culprit.

 

[Bill Roosa]

Check the fuel lines on the injectors too

 

[HUDSON]

thanks a bunch

 

[NYSail]

Run the boat and keep your head in the engine compartment and watch

 

[arf145]

I had a Yanmar fuel pump start leaking when running (broken diaphragm, I think), but I would have thought a mechanic would have caught something like that. I'd be doing what @NYSail said: clean the engine as best you can to make the leak more obvious, and then run the engine and watch, smell, and feel.

 

[Brazil]

I have the 3QM30H. Had a fuel leak only under power. Turned out to be one of the banjo bolts on the fuel return to the filter. It uses copper crush washers above and below. Upon removal and inspection, the bolt is twisted in shear almost to breaking. It is only a hollow tube with a cross-drilled hole. That hole is now a long ellipse. Toad Marine has replacement banjo bolts and crush washers.

During diagnosis, I wrapped strips of paper towel around every joint. The leaker turned wet after running the engine a while.