Leaking fuel filter

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fearmhuir

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I have a Yanmar 3JH3 engine, which I service myself. Since 2008 I have changed the spin-on fuel filter on the engine, and just tightened it by hand.
The same was done early this year, but at the end of a trip around Ireland (with a lot of motoring) it suddenly started to leak around the top of the filter. I had to tighten it with a filter spanner to stop the leak.
It was fine for the last few days of the trip, but assuming that the filter might have been blocked, I changed it, and had the same problem with the new filter. It had to be tightened pretty viciously with the filter spanner.
I had a case of diesel bug last year, but the tank was cleaned out, and all the filters were changed at the beginning of the year, and I am sure there is no residual problem.
When the filter was off, I checked that there was nothing on the filter housing that would interfere with the filter sealing ring.
Is there something else that would cause this filter to leak?
 
If both filters were purchased together could be a faulty batch? Perhaps another filter will solve the problem.
You seem certain there in no old seal or part of a seak eft in place and stuck to the filter housing. Might be worth another look.
 
Depending on the fuel system set up (not familiar with yours to be homest) he only thing other than a bad sealing surface....might be the fuel return lines being blocked or restricted.
 
Thanks guys for your input. I had thought about the return being blocked, but the return pipe is not pressurised at all, and it gets warm all the way back to the tank, which would indicate fuel is being returned ok, but maybe I should remove the return line and put a short length to run into a can to check .
I have never cleaned the thread Sandy, apart for a wipe with a kitchen roll, so maybe have a look at that too.
The thing that puzzles me is that the filter was fine for about 75 hours of motoring and then suddenly leaked, which maybe means QBhoy is on the right track.
Will investigate further, and report back!
 
Worth a try. If it’s all tight and sealing, one would imagine only a higher back pressure than normal would cause such a problem. Unless there is a check or non return valve between the filter and injectors. Unlikely I’d think.
 
I have had a persistent slight leak from my primary fuel filter on engine, it's a yanmar 2GM, and I found an old ybw thread advising a thicker o ring will sort, as it was thought the threaded extent insufficient to properly bed the standard yanmar o ring. so have bought that, not fitted yet. Not sure if relevant to your engine.....
 
did you lubricate the rubber gasket with a bit of fuel prior to screwing it up, this can make quite a bit of difference to the amount of tightening you can do by Hand??
 
Thanks to everyone who posted, and here is the story so far:
The original problem occurred on the filter that I had fitted at the beginning of the season - which I bought from ASAP. After about 70 odd hours motoring, it started to leak - not just a drip either - quite a lot of diesel could be seen running down the outsides of the filter housing and it had filled the engine drip tray.
I tightened it up, and that solved the problem.
However, when I got back to Bangor, I got a new filter by quoting the number on the old filter - and got one in a motor factors with a different number, but was told it was an 'equivalent' filter.
On fitting, it had to be done up with a filter wrench to stop it leaking.
Following up on QBhuoy's suggestion - that the return line might be blocked, I took off the return line, and it was clear. A light blow and I could hear it bubbling in the tank.
I then followed up on Sandy's suggestion about cleaning the thread, so I took off all the hoses, and removed the filter housing.
With the housing in the vice, and unscrewing the filter, I noticed that the filter edge was tightening down on the edge of the housing. So I had been using the wrong filter, and trying to get a metal to metal joint!
I have now ordered five of the usual filters from ASAP which I know fit, and assume that this will make for a normal hand tightening of the filter.
It doesn't explain however, how the original filter suddenly started leaking, as there is no sign of a restriction on the return side.
Has anyone experienced a filter unscrewing itself in service?
Thanks again to everyone for taking the time to reply!
 
I was development engineer with a leading automotive filter company for 20 years in my experience it would be very unusual for a filter to become unscrewed in service. at one time we did have an issue with rough spotwelds under the rubber gasket snagging the gasket when it was tightened....... this caused a few complaints of leaking during service.
 
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