//// 2 fuel tank nightmares ////

Hi All,

My 1999 international 4700 truck has 2 fuel tanks and its driving me crazy.

FWIW - The drivers side fuel tank is small and the passenger side tank is large.

It seems when I drive the truck a lot the 2 tanks empty simultaneously which is good to me since it means it is either sucking from each tank equally and there is a "connection" between the 2 tanks to keep the levels balanced OR it's sucking from 1 tank primarily and there is a "connection" to keep both both tanks at the same level (this second option is what I think is happening....read below to see why)....

In any event, my real problem happens when I park my truck.....

when I park on the street curb, fuel transfers by gravity from the small drivers side fuel tank and fills the larger passenger fuel tank to overflowing (My helper once failed to tighten the passenger side tank which was filled fairly high (maybe half or so) , then filled the smaller driver side tank to "top it off" and parked the truck ....

Within hours much of the fuel transferred from the small tank and overflowed the large passenger tank (with the loose lid) and it made a stream of fuel down the street ....(even without spilling fuel out the larger tank, the small tank seems to always transfer fuel to the large fuel tank (due to the crown in the road and us parking on the street) .

To make matters worse, when he drove the truck so much fuel ran from the small tank that the truck ran out of fuel despite the full large passenger side fuel tank (the gauge also read full since I believe it reads from the large passenger side tank).

How is this problem normally dealt with?

It's been a real pain for me to fill the truck with 12 gallons of diesel from 2 fuel cans to ensure enough fuel is in the small tank to make it to the gas station....

Thanks in advance for any and all help.

Usually they will have a crossover pipe from the bottom of one tank to the bottom of the other. Overflowing is a common complaint. Sometimes they have a hand valve to stop it. I have heard of dual draw systems also. Either one would overflow just the same. If the truck is drawing and returning from the small tank you might either consider relocating the draw to the larger tank and just running one tank or closing the crossover valve, if equipped, when parked. More investigation is needed but it should not be hard to see this stuff.

We had this happen and it was the tank vent. If i can and they let me i remove one tank this saves alot of problems down the road ii also makes working on most trucks easyer.

HI
Thanks for the replies so far....
In researching even more on the net it seems to be a fairly widespread problem...
I'm thinking about trying for a set up like my old ford van had....A flip switch inside the gas tank to select fuel tank...
I never had issue with that system except for the 1 time in 15 years when the switch over valve stopped working....sure beats a daily potential headache!
I also thought of just running 1 big tank but I read somewhere where a 125 gallon tank may cause the frame to flex under he weight....
so many decisions ....
Thanks
Andrew

There are generic electric dual line fuel selector valves available everywhere on the net, it is true.

Your in luck... I just fixed this issue in a large Navistar, it would suck down the smaller 75? gallon tank and lose prime (Series 60 Detroit), of course the gauge sender was on the larger 100 gallon tank. Plugged vent tube on the big tank. The owner had this issue for 3 years.
Being a 1999, I doubt yours has a low mounted crossover line (bottom of one tank to the other) most have a suction line that tees to both tanks and a flow divider to return fuel to both tanks. I'm not sure about the smaller trucks but the one I just fixed had a float in the vent to close it before the tank could overflow through the vent if one tank siphoned over too the other, clean your vents, keep the caps tight, and try to keep both tanks filled to the same level when fueling. And DONT OVERFILL, keep it down 3-4" from the top of the neck.

Birken Vogt said:

There are generic electric dual line fuel selector valves available everywhere on the net, it is true.

Click to expand...

No... Don't do that, just make the stock stuff work again. Most all top draw systems are zero trouble 'til one little thing gets out of whack. Air leak in a hose, PLUGGED VENT, I have also run into foreign objects in the dip tube (hose little silver foil seal on fuel treatment bottles, etc.)

if you are running just a few miles cut the small tank off and just run on the big 1.
I have an 86 freightliner had same problem and it had the bottom transfer line did want it caught sticks so I cut it off and run on 1 tank