Diesel Fuel Return

[BelleAurore]

I’m looking for information on how much fuel my Detroit 4-53 natural engines return to the tank per hour of run time. I know they burn (approx numbers) 6.9 GPH @ 2000 RPM with 8.0 knot cruise. They burn 2.7 GPH @ 1400 RPM with 6.2 knot speed. But, I’m not sure the total gallons I’m running through each engine per hour. I saw a number of 2.3 times burn but that seems low for these engines.

 

[sunchaser]

Maybe disconnect the return line and measure the flow ?

 

[Lepke]

The fuel pump either has 1/4" or 3/8" gears. Probably 1/4. It pumps about 20 gph at speed. In your case returning about 17gph.
Sometimes the pump has been replaced with a 671 pump and that's 35 gph.

 

[garbler]

It’s been a while but I seem to recall about 50% maybe even 75% of fuel to a Detroit unit injector is returned. Either way it’s lot of fuel. The Detroit 53’s, 71’s, 92’s and the old 110’s were all unit injected and these are cooled by return fuel. Return fuel is on these engine is a serious flow as injectors of this type need cooling and fuel tanks get warm.

Sorry for being so vague

Rick

 

[garbler]

Maybe disconnect the return line and measure the flow ?

And what burn up an injector ?

 

[Comodave]

They return so much that they are a pretty effective fuel polisher.

 

[garbler]

They return so much that they are a pretty effective fuel polisher.

Now that is interesting

 

[mmullins]

I don't understand how disconnecting a return line would "burn up an injector?" The same amount of fuel is running through the injector. It's simply being returned to a different location.

 

[garbler]

I don't understand how disconnecting a return line would "burn up an injector?" The same amount of fuel is running through the injector. It's simply being returned to a different location.

Actually a good question and right now I’m trying to visualize the fuel path but my brain gets in the way. However I wouldn’t try it unless you had a mechanic say it’s okay. But honestly if you need to know how many gal per hour is returned I think it would easier a Detroit 53,71 series service book.
In other words I don’t know

Rick

 

[sunchaser]

Rick
I’ve been around DDs where the return is piped into a manifold. From that manifold selector valves are used to return fuel to any number of tanks.

I’ve no idea as to whether the OP’s vessel has such a readily accessible manifold. If it does it may be quite easy to disconnect the line from the manifold and divert it to a 5 gallon marked container. With a watch and a bit of effort the return rate becomes known.

If the OP’s vessel has fuel tank sight tubes and a valved manifold, the return rate is easy to determine. No line disconnecting or instruments needed. This is how I do it.

But, why is knowing the rate necessary? Maybe the OP could chime in.

 

[jagates10]

Rick
I’ve been around DDs where the return is piped into a manifold. From that manifold selector valves are used to return fuel to any number of tanks.

I’ve no idea as to whether the OP’s vessel has such a readily accessible manifold. If it does it may be quite easy to disconnect the line from the manifold and divert it to a 5 gallon marked container. With a watch and a bit of effort the return rate becomes known.

If the OP’s vessel has fuel tank sight tubes and a valved manifold, the return rate is easy to determine. No line disconnecting or instruments needed. This is how I do it.

But, why is knowing the rate necessary? Maybe the OP could chime in.

I've used the return fuel to level the boat and equalize the amount of fuel in other tanks BUT you really have to watch it close.

 

[jleonard]

I've used the return fuel to level the boat and equalize the amount of fuel in other tanks BUT you really have to watch it close.

Yes VERY close. I have the T shirt.

 

[BelleAurore]

I’m looking at flow sensors. Big difference in price for 40gph vs. 100gph

 

[markpierce]

I’m looking for information on how much fuel my Detroit 4-53 natural engines return to the tank per hour of run time. I know they burn (approx numbers) 6.9 GPH @ 2000 RPM with 8.0 knot cruise. They burn 2.7 GPH @ 1400 RPM with 6.2 knot speed. But, I’m not sure the total gallons I’m running through each engine per hour. I saw a number of 2.3 times burn but that seems low for these engines.

Is it important or just curiosity?

 

[Captain Doug]

I put Flow Scans on my twin DD 6-92s to not only map fuel flow by rpm but it has a fuel totalizer. Fuel tank level sensors don’t work well and if I fill the tank I know what I used and gave me confidence in my fuel remaining.

 

[garbler]

I like Floscans and never heard a reliable bad report about them. I used to date a chick who was an accident investigator for the FAA who she told me, between drinks, that Floscans were built primarily for the aircraft industry. Actually I could have used a Floscan on her one time at a wine bar. Good instruments

Rick

 

[garbler]

I put Flow Scans on my twin DD 6-92s to not only map fuel flow by rpm but it has a fuel totalizer. Fuel tank level sensors don’t work well and if I fill the tank I know what I used and gave me confidence in my fuel remaining.

Now those are nice powerful engines in fact my favorite Detroits along with the old 6-110’s. They didn’t last as long as they should have but dimensionally, for their output, are small enough to fit in almost all boats requiring this level of performance.

Rick