MD6B return line routing

[Stu66]

Hi all,

Can anyone tell me please what is the correct routing for the return line on this engine? On the boat I’ve just bought (1976 Golden Shamrock 30’), it runs back to the primary filter. I read that Md7’s have it running back to the secondary.

The background to the question is I have an issue with the engine cutting out at higher rpm. It was running fine before I replaced filters & all the hoses. Thinking I’ve got issues with air in the fuel system.

thanks

 

[Ink]

I'm not an expert on either of these engines but my preference would be to have the return back to the tank.

Depending on how close either of the primary or secondary filters are to the engine could mean hot diesel not getting cooled and could lead to issues with the injection pump.

Just a thought.

Ink

 

[VicS]

Hi all,

Can anyone tell me please what is the correct routing for the return line on this engine? On the boat I’ve just bought (1976 Golden Shamrock 30’), it runs back to the primary filter. I read that Md7’s have it running back to the secondary.

The background to the question is I have an issue with the engine cutting out at higher rpm. It was running fine before I replaced filters & all the hoses. Thinking I’ve got issues with air in the fuel system.

thanks

The fuel system diagrams in the parts catalogues at Volvo Penta parts and accessories - MarinePartsEurope.com show the fuel pipe layout
MD6A/6B/7A/7B all appear to be the same
#36 is the leak off, but returning to the tank will get rid off any air more easily
View attachment 1640610948028.png

 

[Stu66]

The fuel system diagrams in the parts catalogues at Volvo Penta parts and accessories - MarinePartsEurope.com show the fuel pipe layout
MD6A/6B/7A/7B all appear to be the same
#36 is the leak off, but returning to the tank will get rid off any air more easily
View attachment 127723

Thanks Vic. I guess the boat must have come from the factory with the return line running to one of the filters, as the fuel tank only has a fill & vent fitting at its aft end, & the outlet forward.

I was considering connecting the return to the secondary instead of the primary. Any benefit in that or should I just leave it as it is?

Since the pic below was taken I’ve since bypassed the electric pump, and the lift pump has been replaced.

By the way, is there a bleed screw on the injector pump?

tge

 

[VicS]

You will find details on bleeding the fuel system in the Owners manual, which you can download from Engine Manuals and Handbooks | Volvo Penta if you have mislaid your copy
ITYMF that the exact procedure depends on the pump fitted.

The workshop manual may also be useful. Google will find several links

 

[Stu66]

Thanks, I read the manual again and followed the bleeding steps. Primary filter bled ok, so fuel is getting that far with no air.

However, no matter how many times I pump the lift pump (yes it has resistance), no fuel is coming out the bleed screw on the secondary filter.

Having removed the secondary filter again, I can see it’s only about half full of fuel.

Any suggestions?

 

[Stu66]

* Update *

I read a post on a JD tractor forum , where someone had the same problem / exactly the same symptoms I’m having here. Turns out the the first filter was blocked by the seal sitting just inside the top outer edge of the filter, effectively blocking the holes that the filtered fuel should flow through. The correct position for that seal is actually pushed up into the recess of the housing.

Apparentky fuel would partially flow past the seal when the engine was driving the lift pump, but it had no chance when just pumping with the manual lever, and hence no fuel out of the bleed screw on the second filter.

Anyway, I’ll take a look at that primary filter tomorrow and see if indeed that’s my problem.

 

[Stu66]

Problem solved ??.