Diesel fuel return

[PhilPB]

I have a Perkins T6.354 (165hp) and am curious what the fuel return percentage is while running. I don't have any type of flow meter, which is why I'm asking. I have two tanks (112 gallon each) and keep them balanced via the output and input petcocks, fuel gauges and list while at the dock. I heard from a mechanic that it's about 30% return of un-burned fuel back to tanks but curious as that was just his opinion.

 

[Nick F]

Disconnect the return line and stick it in a plastic jug. I did this for my Ford Lehman and measured about 100ml per hour.

 

[Comodave]

Lehmans return almost nothing and Detroits return a whole lot. Not familiar with Perkins though.

 

[jgwinks]

I have twin Perkins and I don't know either. Do your returns go all the way back to the tanks? Mine don't, they feed back into the secondary filters. Return rate is kind of irrelevant that way and it saved a lot of piping. The return lines are only 1/8" tubing so I doubt there's much flow at all.

 

[Ken E.]

Lehmans return almost nothing and Detroits return a whole lot. Not familiar with Perkins though.

When I had Detroits, I used fuel return to transfer between tanks when I needed to equalize them. Lots of fuel returned. The B series Cummins I have now return very little.

 

[utclmjmper]

On many diesel engines,, the fuel return is also used to cool different parts of the system( Detroits) some use a lot others don't..>>>Dan

 

[Comodave]

When I had Detroits, I used fuel return to transfer between tanks when I needed to equalize them. Lots of fuel returned. The B series Cummins I have now return very little.

Detroits are a pretty good fuel polishing system.

 

[PhilPB]

I have twin Perkins and I don't know either. Do your returns go all the way back to the tanks? Mine don't, they feed back into the secondary filters. Return rate is kind of irrelevant that way and it saved a lot of piping. The return lines are only 1/8" tubing so I doubt there's much flow at all.

I have two tanks that both go to primary filter, which then feeds one line to the engine. The engine then sends unspent fuel back to a tee, which then has two lines, each going back to a tank. I have petcock valves from each tank for output to the primary filter and two petcock valves coming from engine back to tanks. I do get quite a bit of fuel returning to the tanks which is why I am curious as to what the percentage of fuel is unspent and recirculating back to the tanks.

 

[PhilPB]

When I had Detroits, I used fuel return to transfer between tanks when I needed to equalize them. Lots of fuel returned. The B series Cummins I have now return very little.

That's what I've been doing to equalize my tanks as well.

 

[boomerang]

On our previous boat, a '78 Mainship 34, we had a Perkins 6.354 too. Mainship designed the fuel system so the engine could draw from either tank but the return was fixed to the port tank. I changed that so that the return could be selected also but the return was a dribble, at best. Transferring a substantial amount of fuel by using the engine fuel pump and return was out of the question with a Perkins.

 

[PhilPB]

On our previous boat, a '78 Mainship 34, we had a Perkins 6.354 too. Mainship designed the fuel system so the engine could draw from either tank but the return was fixed to the port tank. I changed that so that the return could be selected also but the return was a dribble, at best. Transferring a substantial amount of fuel by using the engine fuel pump and return was out of the question with a Perkins.

That's interesting. Both of my tanks are plumbed with fuel returns. If I shut off one tank fuel output feed to the engine, keep its input (return) open and subsequently shut off the return to the other tank while drawing from that other tank, I can noticeably change the tank levels. Of course, this is after quite a few hours of running.

 

[Circumnavigator]

All of this cries out for a day tank.


You don't want to return fuel to the filters because, as noted above, the extra fuel helps keep things cool. If you return the fuel to a fifty gallon day tank, you get the cooling effect and you never have to remember to switch the return line to the correct tank.


Of course a day tank takes a little space, some plumbing and a fuel transfer pump, but aside from the advantage above, it also means that you can be sure that the fuel you are drawing from is clean. Without a day tank, if the fuel in the main tank gets stirred up by a gnarly conditions, the fuel filter can become clogged. While you should have parallel filters switchable with a couple of valves, such a clog still means a trip to the engine room with no power on the boat and could happen again. Of course such things always happen when you are in a narrow passage with a cross wind or current.


Jim

 

[catalinajack]

All of this cries out for a day tank.


You don't want to return fuel to the filters because, as noted above, the extra fuel helps keep things cool. If you return the fuel to a fifty gallon day tank, you get the cooling effect and you never have to remember to switch the return line to the correct tank.


Of course a day tank takes a little space, some plumbing and a fuel transfer pump, but aside from the advantage above, it also means that you can be sure that the fuel you are drawing from is clean. Without a day tank, if the fuel in the main tank gets stirred up by a gnarly conditions, the fuel filter can become clogged. While you should have parallel filters switchable with a couple of valves, such a clog still means a trip to the engine room with no power on the boat and could happen again. Of course such things always happen when you are in a narrow passage with a cross wind or current.


Jim

If you have a vacuum gauge on your filter housing and are paying attention even a little, clogging a filter to the point that it stops an engine simply just should not happen. Rough water? What boat does not see water rough enough quite often such that sediment is not being stirred up constantly. Watch the gauge and change it when it is time.

 

[Circumnavigator]

If you have a vacuum gauge on your filter housing and are paying attention even a little, clogging a filter to the point that it stops an engine simply just should not happen. Rough water? What boat does not see water rough enough quite often such that sediment is not being stirred up constantly. Watch the gauge and change it when it is time.

"Should" is a big word at sea. In gnarly conditions, how often do you go into the engine room and check filter vacuum?


My experience has been that serious sediment is stirred up only when in a gale offshore. What happens when the second filter clogs? I have a pretty strong stomach, I don't want to be changing fuel filters in a gale offshore.


A day tank gives you the assurance that you have a supply of fuel that has been filtered once and is a whole lot easier to keep very clean than main tanks (5,000 gallons on Fintry, 480 on Morning Light).


Jim


Sweetwater -- Swan 57 sloop on which we circumnavigated 1995-98
Fintry -- x Royal Navy Fleet Tender -- owned 2003-2022 18,000 miles including trans-Atlantic The Fleet Tender Fintry
Morning Light -- Webbers Cove 42 single screw trawler 2021- 23
?? Going back to sailing after Morning Light is sold.