finding (and fixing) diesel fuel leak on yanmar

PaulR

PaulR

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our boat has a yanmar 3gm which we find superb - except - for one irritating thing - our engine has a very minor fuel leak which I am struggling to find and cure!

The leak does not stop the engine starting or runnning but after running for a few hours we get a few drops of diesel fuel under the engine and by wrapping toilet paper round various pipes I thought I had narrowed down the leak to the fuel lift pump connecting pipe running to the yanmar fuel filter close to it,

I have replaced the copper washers on the pipe (both washers both ends of the pipe) - still leaks - I have tried using a flexible sealant as recommended on this site also with the washers- still leaks - I am wondering now if the leak is actually coming from the gasket of the lift pump and if the leaking fuel then dribbles from the pump onto the connecting pipe which is why my toilet tissue test was showing diesel on the pipe (lift pump side only) - has anyone replaced the main gasket to the lift pump and is that likely to be the source of the leak?

From what I can see the lift pump is secured to the block by 2 bolts and is operated by a lever so I guess should be easy to remove and replace (even with the tight access to that side of the engine) - the top of the lift pump appears to be held in place with set screws so again guess should be easy enough to take apart - replace gasket - and reassemble but before doing so wondered if anyone has experience of this as a leak point and if replacing the gasket is likely to be as easy as I am hoping (and most importantly fix the leak)

lastly is it best to just use a new gasket or also use a flexible gasket sealant?

determined to beat the leak !

thanks all
 
I've recently suffered from an unusual fuel pipe leak. It was eventually traced to a pinhole so small you could hardly see it.

I throw that in for what it's worth.
 
PaulR said:
...I thought I had narrowed down the leak to the fuel lift pump connecting pipe running to the yanmar fuel filter close to it...
Click to expand...

Are you sure it's not coming from the Yanmar fuel filter itself?

It seems to be a common fault that the metal fuel bowl on the little Yanmar fuel filters doesn't seal to the filter head properly as the serrated securing ring bottoms out on its threads before applying sufficient pressure to the stock O-ring.

Fitting a slightly fatter O-ring cures this.

Worked to eliminate a leak on our 2GM20 (same filter), and has been discussed here previously (should you seek confirmation....)

I can't remember the O-ring size, unfortunately.

Andy
 
Fuel Lift Pump

The pump is easy to take out-remove the 2 bolts and pipes and lift out. However, it is not user serviceable and if leaking normal advice is to put in new one-about £70 from Yanmar-may get one a bit cheaper on ebay. May need a new gasket for pump to engine block connection-although in the past I have got away without this.

Hope this helps.
 
Check the filter again?

Despite your protests, if the filter casing is old it will almost certainly leak a bit: the bleed screws or the unions or the o ring on the bowl. It seems to be made of a very soft alloy that can't take being torqued by repeated filter changes. Fuel will dribble down that pipe from the filter end.
 
Sorry to resurrect this long dead thread. I found it by searching as this seems to be the same problem I am having. A persistent diesel leak of significant proprtions whereby after a day of motoring there is a fairly large puddle of diesel under my Yanmar 2GM20F. On one occasion I spent a night moored to a buoy in rough conditions and although the engine was not running the fuel tank fuel tap allowing fuel to the engine was left open and in the morning the entire tank of fuel had leaked out under the engine!
Traced it (I think) eventually to the lift pump where the flange/gasket at the middle of the "clam shell" feels wet. But I'm surprised at the amount of fuel that leaks out. Checked all the fuel pipes, bleed screws, filters etc and no signs of leaks elsewhere and after motoring a short distance I can see a trail under the engine that does seem to be emanating from this part of the engine.
PaulR did you manage to get yours sorted and did you replace the lift pump?
Have any others come across this or does it sound like something else must be leaking?
 
I thought I had the same problem i.e. a leak from the lift pump but it was coming from the fitting on the filter and running down the pipe to the pump. Tightening up the banjo fitting has so far done the trick. I believe you used to be able to buy a replacement gasket for the pump but it's not available anymore.
I would suggest wiping up all diesel, drying all the pipes/filters and pump and tying some coloured paper toweling on the pipes either side of the pump and the filters. Run the engine and watch what gets wet with diesel first. If it's the towelling between the pump and filter then your pump is ok. Bear in mind you could have more than one leak.
 
Thanks Spyro, I had checked for obvious drips from all the fuel pipes without success but will pay particular attention to the fuel line to the engine mounted fuel filter. In February I disconnected this to change the filter and thought I had tightened it up OK but maybe not!
Although the leak seems to be running forward from the rear left hand side (gauging from where it drips under the engine) diesel could be running down to the pump and dripping from there.
It's quite annoying as I'm always wiping up diesel and the boat constantly stinks of it.
 
The banjo fittings on the filter and pump if overtightened can strip the threads in the aluminium bodies. It's a good idea to carefully Helicoil them all before they do.
 
I've also got a leak in a 3gm30... but it seems to be just air, no sign of diesel getting out. I have to bleed the system every time I start up.
 
I also have this problem and still am unable to find the root cause of the leak. Diesel appears from back l/h side of my 3GM and I have recently changed the lift pump - not that easy due to space limitations and the need of a 1/4 inch socket drive. When I took the old one off there did appear to be a leak mark down the side of the engine behind the lift pump but fitting the new pump has not stopped the problem. I live with it still !
 
I had a diesel leak on my Bukh. Myself and an engineer could not see where it was leaking even though we knew it was coming from around the fuel filter after the lift pump somewhere. (I thought it was the lift pump at first). Replacing the filter O-ring and banjo washers did not fix it. Took it off and could see nothing wrong. Engineer suspected it may have a hairline crack not visible unless all was tightened up so replaced the whole unit and bingo, no leak. It was putting about half a litre under the engine in 5 hours running. I can still see nothing wrong on the old unit even though I took it home.
 
You can get a fluid that you mix in with the fuel. It comes with a infrared torch and after running the engine for a while you can see the leak as it fluoresces. It is made by Ring and available on EBay.

Martin
 
Diesel will go though a microscopic hole and generally lets air in. Put talcum powder on every joint, the bleed screw, around the screw-on filter and the filter pump if you have one, and anything else you can think of. You mention a leak in the fuel lift pump and replacing copper washers, be very careful you don't over tighten them it will cause a leak. There is a diesel engine joint sealant which I bought at Halfords but don't know if they still sell it, be worth calling them.
 
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