Question on generator fuel pickup

[compedgemarine]

I have an 81 model 10 Eagle with two tanks. The 6V92 pulls off the right tank and returns to the left tank. does anyone know how hot the returning fuel is? my left tank has an unused threaded port that I would like to use for the generator but want to make sure that it is not going to be sucking in too hot of fuel as it is only a couple of inches from the return. the right tank only has the pickup and no empty ports. If needed I suppose I could drill and tap the top of the right tank but it would make life easier to use the other if the engine return fuel is not going to be a problem. any ideas.
thanks
steve

[muddog16]

Steve, I'm not sure about the returning temperature of the fuel, but just a note that you probably already thought about......you will need a line going down into your second tank for a pick up and  a return also from your generator. The cross over line from both tanks can thermocycle and remove some of the heat but eventually on long trips the fuel temp will come up anyway, but I'm not sure how much! Maybe one of the guys with more experience already knows what kind of temperatures you are needing to know!

[Ncbob]

I am trying to figure out some valid reason as to why the Manufacturer would design such a fuel system.
You don't state whether or not fuel in the left tank is ever usable. Could it be that the intent was to give the engine only cool fuel and at some point reverse the draw/return scenario? Admittedly I haven't had my first cup of coffee yet but.....

Whichever tank you decide to use it's a good idea to keep the generator pickup above the bottom of the tank so that there is no possibility that you can run the coach out of fuel is you are boondocking . Allowing for at least 50 miles of travel after the generator runs out would seem a good figure for a minimum.

It's going to be interesting to find out how and why your fuel system was designed in this manner...or might there have been some other hands in the pie?

Some years ago I ran a 65' Motor Yacht owned by Louis Prima and Keeley Smith.  Both engines drew from wing tanks in the engine room and returned only to a belly tank, which after a long run would fill and overflow...overboard. It took a while to figure how the connections were made since fuel economy was terrible...but it was corrected. Surprisingly it had been this way from day one...and no one challenged fuel consumption until I came aboard.  What a nightmare!

Bob

[compedgemarine]

I assume that it is done to let the hot return fuel cool some. the tanks are connected together with a 1" or bigger line underneath, similar to the way most big trucks are done. when fueling you have to open the fills on both tanks even if filling just one so the other tank vents well enough so that the fuel rises in both tanks at the same time. I would think that the air flowing around the outside of the tanks would help dissipate heat before the fuel gets back to the right tank? is there a temp point for diesel where heat becomes a problem. on the gas cars and boats we always want the gas to be a cold as possible but other than the basic mechanics I dont know that much on the diesels.
steve

[luvrbus]

My geneartor on my Eagle the pickup is from the right tank but I would think after a few hours of driving time the fuel is going to be the same temperature on both tanks I will check that out next time I go on a trip

[Ncbob]

Steve, now that you mentioned the balance line...it makes a bit more sense. Your first post brought me to think that each tank was isolated from the other except perhaps for feed and return valves. But it does keep the fuel in the right tank cooler. I've given though to an air/liquid return fuel cooler but since I log so few miles at a time I just try and keep the tank above half full.

On the boats we wrapped a copper line (fuel return) around the raw water feed line to the heat exchanger on the Detroits.  Made a big difference.

Bob

[compedgemarine]

On the boats we wrapped a copper line (fuel return) around the raw water feed line to the heat exchanger on the Detroits.  Made a big difference.

so in which way did this help? power, efficency, both? if that is the case then it would seem that the cooler the fuel the happier the engine just like on a gas engine. would be interested to know the temp the fuel reaches after a long run and if a cooler could help.
thanks
steve

[makemineatwostroke]

Steve, heres your answer from DD

Fuel continually cycling through and engine causes the fuel in the tank to become heated after extended operation.
Excessive fuel tempertures can affect engine operation.
An increase in the fuel inlet temperture above 90 degrees will result in a brake hp loss of approximately 2% per 20 degree increment fuel temperture increase.
hope this helps as this for marine engines with a fuel cooler

[compedgemarine]

so if I figure out a way to put a fuel cooler on the inlet side to the motor will I pick up a few horses? I would be interested to know what the real world fuel temp gets to. anyone going for a long run with a temp gun?
steve

[tekebird]

really not much of an issue.  I would not bother worrying about it and plumb it as ou see fit

[sivrtnge2]

The fuel in my semi return to both tanks hot. My genset on it doesn't seem to mind.  I don't know how hot it is but it isn't hot enough to burn as we had to remove the fuel and a tank on the side of the road one day after running it several hundred miles. The genset is sitting directly behind the right side tank which is where it draws from.
--
BILL

[makemineatwostroke]

Steve your fuel is not going to get as hot as sivrtnge2 he must have a engine with a common rail thats over 20,000 psi compared to the 65psi on a 2 stroke and pressure makes heat ,so hook your generator to the fuel tank and don't worry about it