fuel return line

[Han]

Hi All

We're replacing our engine and as a part of the process we have to revamp our fuel system. One of our tanks currently does not have a fitting to attach a fuel return line from the engine. Our two options seem to be:

1. drill and tap for a new fitting on the tank

or

2. tee into our fuel fill line

Drilling and tapping seems most logical, but we're worried about the shavings from drilling ending up in our fuel, so we're thinking we'll go with the teeing option. Is this a valid concern? and does anyone see a problem with teeing into our fuel fill line?

Thanks as always for your help.

[fcsob]

I would use one tank as my primary feed & transfere the fuel with an electric fuel pump. Also use a fuel filter in between.

[Alan Wheeler]

Tee into your fuel line. It is quite satisfactory. Ensure it returns to the tank side of the lift pump. Do not tee into the pressure side of the lift pump. It is a very common way of returning and solves many issues. One being warm fuel retuning to the tank creating condensation.

[Han]

So teeing into the fuel line doesn't cause problems with air in the lines? We considered this, but gave up on it because we thought that we'd end up with bubbles in our fuel supply to the engine. If it would work, it would be an easy solution.

[DeepFrz]

Teeing into your fuel fill is a bad idea because your return line should extend to near the bottom of your tank so as to not aerate your fuel. Teeing into the feed line is better than teeing into the fill I think. I'll let others address the air bubble possibility.

[fcsob]

No you wont have air in you line but the fuel reciculated back to you fuel pumps & injectors will be warm to hot. As a auto tech for 35 years I don't agree with the t concept. You want the fuel to be cool. My first post was not all that clear. Only ever fill the second tank & transfer the fuel to the primary tank. With the filter in line your primary tank only sees clean fuel. I asume the fuel is diesel,use only approved diesel fuel line & transfer pump.

[Alan Wheeler]

Let me say again. Teeing into the line is quite acceptable and is commonly done with no issues. The return line fuel is a dribble of fuel. I think some of you think it is some big volume of fuel. It is not. In fact, at certain times there is virtually no fuel being returned a all. Nor is the volume/temp large enough to cause issues with heating the fuel going to the pump. The IP heats the fuel much hotter than the fuel in the return line ever will. And no, there are no air bubbles. Teeing is OK and safe and has no operating issues and is a very common approach.

[MidLandOne]

Another place one can tee in is on the tank vent (and that is how ours is done).

I also agree with Alan's comments.

[Han]

I hadn't really considered the fuel vent line, is there any potential problem with this? What if the tank needs to vent while there is fuel flowing in, would this cause a bad situation?

[gosstyla]

Originally Posted by Alan Wheeler

I think some of you think it is some big volume of fuel. It is not. In fact, at certain times there is virtually no fuel being returned a all. Nor is the volume/temp large enough to cause issues with heating the fuel going to the pump...

Believe to some extent that depends on type of engine - certainly not the case if they are common rail diesels. With those return volume can be very high and very hot if fuel coolers not used on the return.

[Alan Wheeler]

High pressure fuel rails with electronic controlled injectors are a different beast altogether and still quite new to the game. I doubt many here would have one of these engines yet.

[rodney_k]

FWIW, My Yanmar 4JH2E returns about 10 - 12 gallons per hour to the fuel tank. Much more than I expected. How do I know? I use separate valving on the intake & return lines to select which of 3 tanks to draw fuel from and return fuel to. I transfer fuel from tank to tank as desired by drawing fuel from one tank and returning fuel to another while I am motoring. An example: My forced air diesel heater is plumbed into a separate tank near the heater. By returning fuel to the diesel heater tank while motoring, I can top it off in a very short time.

[MidLandOne]

Originally Posted by Han

I hadn't really considered the fuel vent line, is there any potential problem with this? What if the tank needs to vent while there is fuel flowing in, would this cause a bad situation?

I can only imagine the tank venting out the vent if one was refueling the tank at a high flow while the engine was running - but I suspect likely not a problem if the leak back connection is in the vent close to the tank (as ours is), but never tried it myself.

Under normal engine running circumstances the air flow, very small though it will be, will be into the tank so not a problem and we have never experienced any issues.

[Han]

Thanks everyone,

MidlandOne, your solution sounds reasonable. I hadn't really considered that air is flowing into to the tank the engine is running. We can tee in right at the tank, so hopefully it will work for us as well.

[never monday]

this is one of the few times I'll recommend a Racor smaller than the 500 series.
If you use a 200 series there are two inlets and one outlet. Problem solved.