QSB Fuel Cooler/Supply

[roborr24]

Let me start by saying THANK YOU to those who contribute here. I am extremely thankful for the wealth of information that is available. I a 38′ Scarborough with twin QSB 5.9 380’s. Have been going through them this spring with many updates and maintenance that would not have been possible without all of the insights available. So far I have installed SMX water pumps, new port gear cooler, new bulk fuel filter system w/priming bulb, serviced heat exchangers and after coolers, serviced the port turbo & replaced w/new gaskets etc…, and have ordered the Enviro-vent CCV system to replace my rusting, paint chipping, air-sep system.

My final project for this spring is replacing my starboard fuel tank. I have a few questions regarding the fuel system plumbing that I have not been able to find a consensus on. I bought the boat used, and now that i’m digging into the fuel tank plumbing, it appears it is not set up properly.

1. I have an 19′ run from my tank pickup to the engine lift pump (includes filters). What size fuel line is recommended for this run? Is there a particular type of fuel line that is recommended above anything else? This is a 150 gallon 1/4″ aluminum tank, which is situated below the cockpit deck approximately 3′ aft of the engine room.

2. Where should the fuel cooler return line tap back into the tank? Specifically, should it be tapped into the top of the tank, bottom of the tank, or t’ed into the fuel supply line? Right now it feeds back into the engine fuel supply line, which I now understand defeats the purpose of the fuel cooler.

3. The pickup on my old tank was just a threaded hole in the very bottom corner of the tank that the fuel supply line connected to. Is this the best way to do it, or is it better to have a pickup tube that comes from the top of the tank?

4. What is the best way to test/determine if I need my fuel cooler? We fish a lot during the summer months in 90 degree heat, and I normally cruise about 2250rpm’s. As it has been feeding back into the supply line and I haven’t experienced any issues I assume it is not needed, but before removing I would like a more quantitative assessment. Should I take temperature readings of my tank during the summer months?

Thank you much for any and all insights.

Topic

[Rob Schepis]

Robert, I was thinking mechanical when I advised on the submerged fuel return. As per Cummins, the common rail engines do not use submerged returns. See attached.

[roborr24]

Rob,

Thank you much for the quick reply. Some of these things seem intuitive, but it doesn’t always work out that way. I am grateful for experienced input.

Plumbing her up tomorrow and hopefully we will be ready to roll for the season.

Robert

[Rob Schepis]

Thanks for the acknowledgment. You’ve been busy. All great stuff.

1. Should be fine with 1/2″ ID (type USCG A-1 ) unless you have a multitude of fittings, valves, etc etc along the way.

2. Return line on a diptube (submerged) and not right next to the supply is best. Current T’d in setup not preferred as you noted.

3. Bottom tank supply is fine. Would be best with a drainable sump but it’s likely just a flat bottom, right? You’ve got the bulk filter now so let it do it’s job..

4. I think you answered your own question as to the fuel coolers. Sure if you ran around with very low levels in the tanks for very long long days the fuel temp would rise but would you even notice during normal use…..

[Author]

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