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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > Yanmar 2QM15 return fuel line leak
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Topic Review (Newest First)
03-14-2012 01:26 AM
RichH
Re: Yanmar 2QM15 return fuel line leak

Typical engine life on the Yanmar Q series is 8-10,000 hours if well maintained. Dont forget to change the trans. oil every now and then. :-)
03-14-2012 12:42 AM
boatjames
Re: Yanmar 2QM15 return fuel line leak

thanks Rich H for your thoughts, I'd read elsewhere this was not an ideal system - the engine is 30 plus years old I think (and the design may be older), so at this stage of it's life I am looking at just nursing it along as long as I can (or until $20k falls from the sky to re-power!). Having said all that, another mechanic raved about this model engine saying it had stainless steel internals or something and was one of Yanmar's better designs...
03-11-2012 10:37 AM
RichH
Re: Yanmar 2QM15 return fuel line leak

Quote:
Originally Posted by boatjames View Post
However on 2QM15 the fuel return line feeds the fuel back into the fuel filter for more immediate re-circulation. So, that being the case, is pressure still not an issue?
IMO - very BAD practice and of little practical value for 'filtration':
1. causes backpressure against the high pressure pump. Can yield a too rich mixture, unless injector timing is 'readjusted'. return line should discharge to near 'atmospheric pressure'.
2. Too little oil flow in the return line to be of 'benefit'. Pressure too low for effective motive pressure 'across' the filter; filters require 'work' to make them operate with efficiency, therefore needing 'humongous' filter surface area to keep 'pressure drop' across filter 'reasonable' or 'choked' return flow. see #1 above.

Recommendation: If you have a 'crudy' tank that requires inordinate amount of 'filter change', use a separate / independent 'fuel recirculation polisher' ON the tank and 'unconnected' to the main fuel distribution system ... then the 'fuel distribution system' will 'hardly' ever become 'challenged' with debris, etc. Such a std. 'recirc polisher' system requires that you 'start' with a pristine / cleaned tank. On a small hp engine the Recirc polisher can be 'quite small'. The amount of 'tank turnover' filtered at ~10-20ĶM will keep the tank at approx. 'sub-micronic' sized particles - a 'mathematical trick'.
On a practical basis, if your current filter usage is small, the tank internals are clean, then simply remove the 'polish' filter on the return line; but, install gages on the 'racors' so you know 'when'/if to change them ... before you 'crud up' the 'racors' and stall the engine. ;-)
03-10-2012 11:04 PM
fryewe
Re: Yanmar 2QM15 return fuel line leak

James, that's pretty nasty looking. Looks like you're getting salt water on your engine, and that's likely why the line failed. Makes no sense that it would corrode from the inside out, nor does it make sense that it eroded, since the fuel velocity in that pipe should be pretty low.

That return line connects the low pressure and high pressure sections of your fuel system. It routes excess fuel from the injectors back to the fuel filter at the injection pump suction. It should be robust.

With the fuel return pipe off, you should replace the hose clamps on the cooling water hose in just aft of the pipe, and check that hose to make sure it doesn't have a crack in it. It is a molded hose, but you can likely replace it with an unmolded hose. I'd look for other leaks, perhaps from the zinc plug in the front of the engine, and the hose from the raw water pump to the small distribution manifold where the zinc is installed. Have you been replacing your zincs regularly?

Check Torresen Marine's web site for part availability. They have accurate status for part availability. You can call them for pricing, but you'll have to buy it in the region you are in...they can't ship outside their region.

Good luck.
03-10-2012 05:36 PM
boatjames
Re: Yanmar 2QM15 return fuel line leak

thanks for the parts list Daddyhop -- that is really useful and at least I can search and check whether it is still available!

Rich H, thanks for your thoughts. I wonder whether the pressure issue applies here or not, as the circuit I think you are describing is where the the fuel return line returns the fuel to the fuel tank. However on 2QM15 the fuel return line feeds the fuel back into the fuel filter for more immediate re-circulation. So, that being the case, is pressure still not an issue?

I've read somewhere that this arrangement is not a great idea because the fuel is too warm that is recirculated and this can reduce engine performance, however that is how it is rigged up!

Also didn't quite follow how/where the water gets into the fuel return line to form sulphuric acid.

Great tip Rich H re stainless steel piping, and if a replacement part is not available, I'll look into getting one made if the silver solder option is regarded as too unreliable/risky

This is what the pipe looks like (the horizontal one in picture, and you may be able to make out a drop of fuel towards the right-hand end leaking)
03-10-2012 10:15 AM
RichH
Re: Yanmar 2QM15 return fuel line leak

There is no real need for a 'high pressure' line for the 'return' line as it discharges to atmospheric pressure in the tank. The return lines corrode due to possible high temperature and sulfur bearing oil (the sulphur + water ultimately forms Sulphuric acid) ... for ultimate safety replace the engine mounted return line and its 'tail end' COPPER line with double flared stainless steel tubing and not copper tube with 'compression fittings'.
03-10-2012 08:59 AM
daddyhop1
Re: Yanmar 2QM15 return fuel line leak

Quote:
Originally Posted by daddyhop1 View Post
You might try the solder trick, however i think I wold want to know that the part was good and sound next time I really needed the engine to work.
I'll attach a part listing for the file system for a 2QM15, when I figure out how to attach it to this post.
Good Luck!
Here i ste parts List I mentioned.
03-10-2012 08:52 AM
daddyhop1
Re: Yanmar 2QM15 return fuel line leak

Quote:
Originally Posted by boatjames View Post
Just discovered a hole in the return fuel line. Engine runs fine, but obviously fuel sprays everywhere? Can you get the yanmar part (number?) or is there another line that will work I get in Sydney, Australia? Is silver soldering it by a plumber viable? Does it have to be a high pressure line?


Any suggestions welcomed!
You might try the solder trick, however i think I wold want to know that the part was good and sound next time I really needed the engine to work.
I'll attach a part listing for the file system for a 2QM15, when I figure out how to attach it to this post.
Good Luck!
03-10-2012 01:34 AM
boatjames
Yanmar 2QM15 return fuel line leak

Just discovered a hole in the return fuel line. Engine runs fine, but obviously fuel sprays everywhere? Can you get the yanmar part (number?) or is there another line that will work I get in Sydney, Australia? Is silver soldering it by a plumber viable? Does it have to be a high pressure line?


Any suggestions welcomed!

 
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