Yanmar 2qm15 Fuel return bypass??

[Boomer2it]

reading some old threads, I am curious how bypassing the fuel return line direct to the fuel tank was done. I see it's been mentioned but no instructions? Removing and replacing the high pressure return lines and routing a flexible fuel line all the way back to the tank seems like a project. How is new fuel hose connected to top of return and where on the tank does it connect?
Just ordered a new secondary fuel filter housing, stripped the threads and would rather bypass with the new installation. Not sure the new housing will even accept the old banjo bolt. The bold on the new housing looks smaller and doesn't look like it is long enough to slide through the banjo fitting and back into the top of the housing (bleed screw).

"The pictured diagram below shows the routing of the 2QM15's fuel system. As John says if the engine ran and all that is changed is the filters, bleeding the secondary may be all that is needed. I replaced the hoses and fuel pump and had a hard time restarting the engine. After rerouting the return fuel pipe to the fuel tank the engine runs as well as it had before."

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[jssailem]

There is a bit of info and questions packed into this query...

Lets break it down.

1. ..how bypassing the fuel return line direct to the fuel tank was done. I see it's been mentioned but no instructions?
   1. You fit a fuel line hose from the end of the return line (in your image) back to the tank. The design in your image has the return line going back to the filter to feed the main fuel lien and reintroduce your return fuel at the filter. It can be that way, or you can run the line back to the tank. The "to the tank" option just requires more fuel line (hose) and a fitting on the tank to dump the return fuel
2. Removing and replacing the high pressure return lines and routing a flexible fuel line all the way back to the tank seems like a project.
   1. First you are not replacing a "High Pressure" line. The pressure is between the High Pressure pump and the injector to force the fuel into the cylinder. The return line is not considered high pressure. And yes it is a bit of a task. You need to find a path to route and secure the line. Most will follow the fuel line from tank to engine.
3. How is new fuel hose connected to top of return and where on the tank does it connect?
   1. Bit confused on this query. Reconnect the way you removed.
4. Just ordered a new secondary fuel filter housing, stripped the threads and would rather bypass with the new installation.
   1. You can do this. It is not original but it shoudl work. As you say it will take some DIY effort. You will become more familiar with your fuel system and likely the aroma of diesel.
5. Not sure the new housing will even accept the old banjo bolt. The bold on the new housing looks smaller and doesn't look like it is long enough to slide through the banjo fitting and back into the top of the housing (bleed screw).
   1. If the replacement design is not the same then the part is not an exact match to what you are removing.

 

[Boomer2it]

John thanks for the timely response,
I have become quite proficient with bleeding the fuel lines and changing filters, but if I can streamline things and improve that's always the plan.
Not sure where I would cut the return line and then attach a new fuel hose (or what size to use)?
When I get back up to the boat I will compare banjo bolt sizes and if the original bolt fits onto and into the new housing then I will probably just go that route and worry about bypassing the return over the winter on the hard.

Thanks again Gene

There is a bit of info and questions packed into this query...

Lets break it down.

1. ..how bypassing the fuel return line direct to the fuel tank was done. I see it's been mentioned but no instructions?
   1. You fit a fuel line hose from the end of the return line (in your image) back to the tank. The design in your image has the return line going back to the filter to feed the main fuel lien and reintroduce your return fuel at the filter. It can be that way, or you can run the line back to the tank. The "to the tank" option just requires more fuel line (hose) and a fitting on the tank to dump the return fuel
2. Removing and replacing the high pressure return lines and routing a flexible fuel line all the way back to the tank seems like a project.
   1. First you are not replacing a "High Pressure" line. The pressure is between the High Pressure pump and the injector to force the fuel into the cylinder. The return line is not considered high pressure. And yes it is a bit of a task. You need to find a path to route and secure the line. Most will follow the fuel line from tank to engine.
3. How is new fuel hose connected to top of return and where on the tank does it connect?
   1. Bit confused on this query. Reconnect the way you removed.
4. Just ordered a new secondary fuel filter housing, stripped the threads and would rather bypass with the new installation.
   1. You can do this. It is not original but it shoudl work. As you say it will take some DIY effort. You will become more familiar with your fuel system and likely the aroma of diesel.
5. Not sure the new housing will even accept the old banjo bolt. The bold on the new housing looks smaller and doesn't look like it is long enough to slide through the banjo fitting and back into the top of the housing (bleed screw).
   1. If the replacement design is not the same then the part is not an exact match to what you are removing.

 

[jssailem]

Gene... Looking at the images, the fit looks close.

Worth a try. If it works.. I think I would just leave it. Nothing really gained by sending the extra fuel back to the tank. Note the fuel has already been filtered once. Putting it into the filter and then into the stream seems reasonable.

Additionally, the single point would appear, gives you the optimum for fuel line bleeding.

Just my observations.

 

[Jake N Eggs]

I am not sure that adding a return to the fuel tank is streamlining anything. Your set up is designed as a complete system where the Original Equipment Manufacturer only has to feed fuel to the engine. If it were me I would keep it that way.

If you want to change the return to go to the tank you can cut the return pipe close to the injectors leaving enough of the original pipe to support the hose. The hose inside diameter should be the same as the pipe outside diameter. Use 2 clamps as there will be no barb for the hose to bite into. Obviously you would clean the paint and corrosion off the pipe. The return hose goes back to the tank to a fitting beside the fuel suction fitting. If there is no fitting in the tank for this it will make it more difficult as you would have to add a fitting. The return should have a tube inside the tank so that the return fuel is discharged into the fuel in the tank, rather than discharging into the air space at the top of the tank. If it is in the air space it could allow air to backfeed into the fuel system when the engine sits for a while.

If it is your old filter housing that has been stripped at the return pipe connection you can probably repair the threads with a Helicoil. It will be metric.

Good luck.

By the way, you can get a banjo fitting with a small bleed screw in the top to eliminate having to loosen the banjo each time you bleed the fuel system. You can also drill and tap your existing banjo to add a bleed screw.

 

[RoyS]

Agree that you should get rid of that return line to the filter. Modified mine as Jake above described years ago and never looked back. That line to the filter never worked and eventually I had to bleed the air out. I am not sure but I think Yanmar abandoned that design after the short lived 2QM15 series. Extending the return line to the bottom of the tank as Jake described is the right way to go. If your 2QM15 is hard to start cold then there is a further modification with the return line that will cure that also. Shout if you have that hard cold start issue and I will provide more info.

 

[Boomer2it]

I am curious about the cold start modification. I have been thinking about installing a new starter figuring that would fix the prolonged cranking. starter works fine but you do need to crank a few times after boat sits for a few days. But she is an older boat and engine, a little extra cranking is expected......

Agree that you should get rid of that return line to the filter. Modified mine as Jake above described years ago and never looked back. That line to the filter never worked and eventually I had to bleed the air out. I am not sure but I think Yanmar abandoned that design after the short lived 2QM15 series. Extending the return line to the bottom of the tank as Jake described is the right way to go. If your 2QM15 is hard to start cold then there is a further modification with the return line that will cure that also. Shout if you have that hard cold start issue and I will provide more info.

 

[RoyS]

Since you asked: Hard cold start may be addressed with the addition of a Thermostart device. Note that is Thermostart and not thermostat. Device was supplied for tractors using the same motor. It performs like a glow plug which this engine is lacking. It is a small part about the size of a spark plug that screws into an existing port in your intake manifold just behind the air cleaner. Remove the cap on the port and screw in the Thermostart. Connect your injector fuel return line to a small plastic reservoir on the top of the Thermostart and continue the return line on to your fuel tank. Connect a No.10 ga wire to the device from a new additional starter push button mounted next to your existing starter push button. Power the new button from the line side of the existing starter button. The way it works is you press the Thermostart button (alone) and hold it for 20 seconds. Inside the Thermostart a heating coil similar to a cigarette lighter heats up which causes an internal valve to open and allows a few drops of diesel fuel in the small reservoir to drip onto the coil and ignite inside the intake manifold. After about 20 seconds the air inside the manifold is hot. Immediately release the Thermostart button and then press the engine starter button (alone). The heated air is now drawn into the cylinders and your engine starts as if it were already warmed up. There are millions of these in use on diesel engines lacking glow plugs. Purchase from tractor supply dealers. I installed mine in 2016 and it has worked flawlessly since that time. I carry a spare Thermostart but have not yet had to use it. Photo below:

 

[Boomer2it]

Interesting.....Thank you

Since you asked: Hard cold start may be addressed with the addition of a Thermostart device. Note that is Thermostart and not thermostat. Device was supplied for tractors using the same motor. It performs like a glow plug which this engine is lacking. It is a small part about the size of a spark plug that screws into an existing port in your intake manifold just behind the air cleaner. Remove the cap on the port and screw in the Thermostart. Connect your injector fuel return line to a small plastic reservoir on the top of the Thermostart and continue the return line on to your fuel tank. Connect a No.10 ga wire to the device from a new additional starter push button mounted next to your existing starter push button. Power the new button from the line side of the existing starter button. The way it works is you press the Thermostart button (alone) and hold it for 20 seconds. Inside the Thermostart a heating coil similar to a cigarette lighter heats up which causes an internal valve to open and allows a few drops of diesel fuel in the small reservoir to drip onto the coil and ignite inside the intake manifold. After about 20 seconds the air inside the manifold is hot. Immediately release the Thermostart button and then press the engine starter button (alone). The heated air is now drawn into the cylinders and your engine starts as if it were already warmed up. There are millions of these in use on diesel engines lacking glow plugs. Purchase from tractor supply dealers. I installed mine in 2016 and it has worked flawlessly since that time. I carry a spare Thermostart but have not yet had to use it. Photo below:
View attachment 196053

 

[MikeHoncho]

When I replaced my fuel tank I added a fuel gauge sending unit. You can get them with a integrated fuel return port. That's what I used. The original tank had a "T" in the tank vent for the return. I didn't like it.