Volvo 2002 Fuel return

[Jwoods]

I am having a new fuel tank made and when we discussed the specification it was considered easier to omit the fuel return pipe and feed this into the inlet stage of the primary filter. I had not thought this through enough as there are two return with this engine! It is the injector spill pipe that is routed to the secondary (engine) filter and it is the fuel pump spill pipe that goes back to the tank.

Has anyone any idea how much fuel flows through this pipe? Can it be fed back after the tank? As far as I can see the lift pump feeds both pumps and it is possible that fuel would circulate past the second pump quite easily!

Any info greatly received folks!

 

[johnalison]

I seem to remember reading that a quarter of the fuel is burned & the rest returned to the tank. This was a problem on our last boat as the tank got fairly hot and the cool-box was only separated by a thin bulkhead.

 

[WayneS]

I also seem to remember that feeding it back to the tank allows the fuel to cool again. Feeding it back into the supply could, I imagine, result in very hot fuel.

W

 

[P4Paul]

You could feed both leak-off pipes back into the filler neck of the tank.

The excess fuel is used for cooling and lubrication of both pump and injectors, so as things wear the more fuel leaks off which if not cooled offers less lubrication the next time around adding to the wear in the pump and injectors.

Don't forget that the tank also needs a breather, so three pipe connectors would be needed on the filler neck.

It is important that the leak-offs and breather are at different heights (breather higher) and angled downwards so you don't just pump the fuel straight out the breather and overboard.

Hope all goes well,

Paul.

 

[nigelhudson]

On our VP 2002 the return is taken off the aft injection pump and goes direct to the tank. It is noticeable after 5 hours of continuous running the tank temperature is significantly increased. As the engine feed is taken from the bottom of the tank this means that the coolest diesel is used to feed the engine which contibutes to cooling the pumps.

When designing the return I suggest that you leave a siphon break if the top of the tank is higher than the engine. Our installation lacks this break which means that when you remove the secondary, engine fuel filter unfiltered fuel syphons back through the pumps and flows unchecked out of the filter. It also makes bleeding the filter a pain as the fuel floods out if you use the recommended method.

 

[pampas]

If I am correct the excess fuel is that fuel that is used to lift and compress the spring, after doing its work this is then dumped into the fuel return pipe. Question, if it is so important for the fuel to be cool why are engines fitted with electric fuel heaters?

 

[earlybird]

[ QUOTE ]
why are engines fitted with electric fuel heater?

[/ QUOTE ]
Used to be to stop it freezing in the winter, (on the railways IIRC), no longer happens I believe; due to global warming.

 

[P4Paul]

Fuel heaters originally were fitted to try and resolve the waxing of fuel in cold weather or conditions with high wind chill factors, however, as fuels have become more refined heaters/heat exchangers have become widely used to reproduce optimum temperatures for combustion. These tend to be used on higher spec engines than your average Volvo Penta / Yanmar etc and normally in reply to quite specific circumstances.

The chance of a yacht needed to use a fuel heater to force that extra few joules out of each power stroke is slim, however if your fuel supplier buys the cheapest crud they can, never clean their tanks or filter the fuel, or indeed if you badly manage your own tanks, you could at certain times of the year suffer from symptoms similar to waxing and a heater may help.

Of course this is only my opinion, and as my wife sometimes reminds me - I am capable of talking complete and utter bollocks......

Have a great day,

Paul.

 

[Jwoods]

Many thanks for the informative replies on this one. Looks like I will feed fuel back to filler pipe as this is easiest option!