Does diesel fuel return line have to be above fuel tank?

[Wotname]

Originally Posted by Stu Jackson

Honest question: why? All one seems to need to know is fuel consumption for range planning, i.e., how many hours per gallon or litre your engine uses. How much goes into engine use and how much is returned is immaterial. Interesting to know, but useless for real world operation and boat range.

Honest answer (from my perspective, not Jackos): Jacko's first sentence (post #19) explains it. To see if the degree of fuel polishing is sufficient to be effective.

Take say a 25 litre fuel tank and a 2GM20 engine running at ~ 1litre per hour (consumed). If the return line is returning 2 litres per hour (at that throttle setting), then after 8 hours of operation, all the remaining fuel has been though the primary and secondary filters at least once.

IMO, this is good real world information however I agree it isn't essential!

However if the numbers are different then conclusion is different

[Sailorbob8599]

Originally Posted by jmschmidt

Your problem was they were Volvos, the most complaint ridded power plants in the marine world, as are their cars in the auto world. The car division is owned by the Chinese, don't know if their engine builder is too.

Here we go again, someone spreading negatives & bad-mouthing a proud brand name product with no specifics. I wish you would either state what your personal problem with the product is, before you start bad-mouthing them.
If you knew anything at all about the automotive business, you would know the Chinese are the corporate owners of the Volvo name, but the product is still built in Sweden as well as a number of other countries. If you don't know the truth, please do not bad mouth a good product just because you may have had a bad experience yourself.
I have driven Volvo cars for the past 50 years & never had a problem. I have accumulated more than 300.000 MILES on more than just a few of them, so I think I know what I am talking about; furthermore, many so called "problems" are often found to be caused by improper, or neglected maintenance ... & no, I do not work for Volvo, & have been retired for more than 20 years in the trucking industry. I do own some old Volvo cars with very high mileages & they all continue to run well ... because they are properly maintained.
Although I have never owned a Volvo marine engine, I have no doubt they are equally as good if well maintained. So enough of the bad mouthing unless you have some proven facts to back up your comments. You run the risk of becoming known as a "muck slinger"

[MC2019]

The diesel return in low pressure, so if you don't plumb to top of tank you need to worry about the head that feed would have to over come.

You could add a pump but if it fails you don't get flow on your return line you could burn up the high pressure injection pump.

Originally Posted by er9

want to relocate fuel tank at some point in the future and have been wondering about this recently.

currently fuel tank is under starboard quarter berth and fuel return line (universal 5432) is mostly above the level of the fuel tank but its only 24" distance from engine to tank. If i were to relocate the tank 10' away under the cabin settee would i have to keep the return line above the level of the fuel tank? is 10' too far a distance for an engine to return un-used fuel back to the tank?

also while im at it...if i decided to add a second fule tank...do i have to have a return line to both tanks or just one? does it really matter?

[nrx500]

No, the engine pushes the surplus fuel back to the tank.

[skipperpete]

Hmm, another 2018 thread revival???
This thread was actually worth rereading, seems like everyone thinks that all return lines are the same regardless of what engine type you have and what specific fuel system and injector pump that engine uses. GM, Cummins, Perkins,Yanmar just to mention a few have vastly different expectations on how return line fuel should be managed and generally state why. There is no “one simple answer” and the wrong return system can badly damage either you or your engine.