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Old 03-12-2015, 11:35 AM   #1
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Connect a generator to bus fuel tank??

Hi. I just purchased an Onan 3.5kva diesel generator that is built in to its own trailer, for construction sites/rentals I would assume. My goal is to tap the bus's fuel tank so that I only have to worry about one fuel gauge. My question is. First, is this a good idea? Second, the genny has two lines that run to the existing tank. I'm not a diesel mechanic, but can anyone tell me why two separate lines? I got a really good deal on the generator, and I was really looking for something with more power. Any thoughts on whether this will be enough? I haven't done anything with the bus yet. It's still pretty much just a school bus. I was hoping for some A/C and the bus doesn't have factory A/C, so probably going the rooftop route. I'm sure I'll be adding propane along the way at some point. I'm still looking for a very cheap RV that I can rob for bathroom parts. I still haven't decided exactly what we're going to wind up with yet, but for now the bus will be our Uhaul to get us from Indiana to Florida, and then who knows. I was leaning toward going the "party bus" route, but could wind up going full RV conversion. Anyway, I would appreciate any thoughts on the subject(s).

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Old 03-12-2015, 11:45 AM   #2
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Don't know why two lines. The POS Onan in the Class C only had one line. I do know the fuel line is held up to where it will not pick up the last 1/4 tank of fuel. Why don't you contact Onan?
This post is my opinion. It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
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Old 03-12-2015, 01:12 PM   #3
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One line is the supply line and the second line is the return line.

A car with a gas engine and a carb uses all of the fuel that is sent from the tank to the carb.

A diesel engine uses only a fraction of the fuel that is pumped up to the injection pump. The excess goes back to the tank to be pumped back again to be used.

Using your bus fuel tank is not a bad idea. Just don't plumb the fuel pickup for the genset anywhere below about 1/4-tank.

Running out of fuel for a genset is just an annoyance.

Running the bus fuel tank dry because the genset used up all of the fuel is a major PITA.
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Old 03-13-2015, 01:40 AM   #4
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Another thing to think about on generator fuel is to mount a separate tank on the trailer and label it for off-road diesel fuel which allows you to use the red fuel which
doesn't charge the highway tax which runs at least 30 cents per gallon more than the green colored fuel with the extra road tax applied.
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Old 03-16-2015, 10:11 AM   #5
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Personally I would be cautious with the line due to connecting and disconnecting them. Air in a diesel line is a problem so you would need some special fittings to keep the lines primed during disconnect.
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Old 03-16-2015, 10:20 AM   #6
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Originally Posted by lornaschinske View Post
Don't know why two lines. The POS Onan in the Class C only had one line. I do know the fuel line is held up to where it will not pick up the last 1/4 tank of fuel. Why don't you contact Onan?
Contact Onan? Lol funny.

Your generator had two lines also. You just did not see the other one.

Like has been mentioned, they all need a feed and a return.

If the generator was mounted on the bus, I like the idea of running it from the buses fuel tank.

On the trailer, I would keep the generator on it's own fuel tank. Not worth the trouble.

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Old 03-16-2015, 11:08 AM   #7
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The giant 16KW marine diesel generator that was on my bus when I bought it (former bookmobile) also had a feed and a return line plumbed into the main engine's fuel lines. It's a great idea if you plan to use the genset only occasionally because you'll never have to worry about the fuel supply going bad for lack of use (although this is less of a problem than on a gasoline generator). Also, provided the main tank is near full, you have a practically unlimited source of fuel as most people wouldn't run their generator enough to burn through the entire supply of diesel before their next trip to refuel.

On the downside, as was mentioned, there is the slight chance you could use all of your main engine's fuel, and running the vehicle's engine dry is a bad idea. In my case, the generator's fuel lines were an oily, leaking mess that I was glad to be rid of.
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bus fuel tank, diesel generator, electrical, fuel system

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