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Old 11-29-2022, 06:13 PM   #1
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Diesel Fuel Return

Iím 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, Iím not sure the total gallons Iím running through each engine per hour. I saw a number of 2.3 times burn but that seems low for these engines.
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Old 11-29-2022, 07:41 PM   #2
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Maybe disconnect the return line and measure the flow ?
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Old 11-29-2022, 07:46 PM   #3
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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.
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Old 11-29-2022, 10:35 PM   #4
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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

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Old 11-30-2022, 07:12 PM   #5
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Maybe disconnect the return line and measure the flow ?
And what burn up an injector ?
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Old 11-30-2022, 08:07 PM   #6
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They return so much that they are a pretty effective fuel polisher.
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Old 11-30-2022, 08:21 PM   #7
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They return so much that they are a pretty effective fuel polisher.
Now that is interesting
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Old 11-30-2022, 09:44 PM   #8
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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.
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Old 12-01-2022, 09:28 AM   #9
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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 Iím trying to visualize the fuel path but my brain gets in the way. However I wouldnít try it unless you had a mechanic say itís 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 donít know

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Old 12-01-2022, 09:44 AM   #10
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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.
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Old 12-01-2022, 12:23 PM   #11
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Rick
Iíve 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.

Iíve no idea as to whether the OPís 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 OPís 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.
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Old 12-01-2022, 02:44 PM   #12
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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.
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Old 12-01-2022, 08:01 PM   #13
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I’m looking at flow sensors. Big difference in price for 40gph vs. 100gph
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Old 12-01-2022, 10:57 PM   #14
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Iím 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, Iím not sure the total gallons Iím 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?
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Old 12-04-2022, 12:43 PM   #15
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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 donít work well and if I fill the tank I know what I used and gave me confidence in my fuel remaining.
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Old 12-04-2022, 01:56 PM   #16
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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

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Old 12-04-2022, 02:07 PM   #17
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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 donít 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 6-110ís. They didnít 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.

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