Leaking Fuel Lines??

**billandlori** · 06.23.2012

I have noticed on my 2004 Star w/C15 that my fuel mileage is much better if I keep the fuel level above half full and if I let it get almost empty it won't restart without a re-prime.

Where would be the best places to start looking? It seems like there is a leak in one of the dip tubes in the tanks or something alowing it to suck air?

Thanks for the help!

Bill

**bigdad7** · 06.24.2012

if you haven;t changed fuel lines it is prob time ......had that issue to at about a million miles when i looked at all the fuel lines after taking them off i was shocked at how brittle they were

**bubbanbrenda** · 07.08.2012

There is also a check valve that is supposed to prevent fuel bleed back

**2bit** · 07.09.2012

Buy fuel sight glasses or find a shop that has them. One goes in suction line, the other in the return. Air bubbles in both, the problem is fuel lines or tank stand pipes. Cap off different sections until you find the leak. It's possible one of the stand pipes cracked or could be loose fitting. If only the return line has bubbles the leak is between the glasses. Make sure to look at the mating surface of the flare fittings. The one on my passenger tank had a defect that allowed it to suck air. The lower the fuel level the worse it gets.

**Dice1** · 07.10.2012

Originally Posted by billandlori

I have noticed on my 2004 Star w/C15 that my fuel mileage is much better if I keep the fuel level above half full and if I let it get almost empty it won't restart without a re-prime.

Where would be the best places to start looking? It seems like there is a leak in one of the dip tubes in the tanks or something alowing it to suck air?

Thanks for the help!

Bill

I keep my tanks full also to get better fuel mileage because fuel is used as a coolant for the injectors and returned to the tanks as hot fuel that heats up the rest of the fuel in the tanks with the more fuel in the tanks the lower the fuel temperture going back to the motor the better the fuel mileage.

As far as motor not holding prime, as mentioned earlier the problem could be a fuel check valve in the system not letting it hold prime. My FASS covers this problem up because the electric pump on the FASS primes the system.

**Cowpie1** · 07.11.2012

Daimler shows in all their manuals (Star or FL) to replace fuel lines at 5 years. At least every truck maintenance manual from Daimler I have ever seen.

**turnanburn** · 07.11.2012

I have found suction side leaks on older Cummins by charging the return line with VERY low air pressure.

**heavyhaulerss** · 07.11.2012

my 17 year old fuel lines are still working. maybe I should change them anyway.

**heavyhaulerss** · 10.12.2012

I just changed some of my fuel lines yesterday. ser 60 detroit. I am not sure what purpose each serves, but here is what I replaced. the line from the inlet of my davco to a tee fitting with other fuel lines. both lines from the back of the head, 1 with the back check that went to the prochek & the other, which I think maybe the return line? to the other side of prochek. then from the procheck to fuel pump. they were all original. so I figured it was time to replace. I posted this, cause I have heard of folks changing fuel lines & having problems starting engine. keeping this in mind.. I would tighten one end of a line, the lower end, such as the tee fitting, then I filled the line with diesel fuel, before screwing on to the higher, or upper end of line,such as the davco inlet. so all the lines had a good amount of fuel in them when I was done. I started truck, it ran, sputtered a lil, then leveled out. never had to crank twice, or add ether.