Fuel blow back on 98 Amer Tradition diesel / similar Fleetwood

[mvz944t]

I have periodic issues with fuel blow back out of the filler on my 1998 American Tradition MH (diesel 40'). It can do it when the tank is empty, partial, or near full. I have tried opening the gas cap on the other side and it will blow it out of that side also. I found the vent hose partially crimped where it goes between the frame rail and the tank and I installed some spacers so it is no longer crimped. Air will flow through the vent hose backwards if I attache an air hose to it. Both of the filler hoses have been replaced and there are no kinks in either, and nothing else I can find. I just had the rig in for service at a capable shop and they could find no reason for the blow back. When I mean blow back, I mean blow back! It seems like it is worse when the weather is warm but I don't use it enough to confirm that. If anyone out there has a similar American or Fleetwood and has had the same problem and has found out a cure for it, please let me know.

Thanks,

[Gary RVRoamer]

It's hardly unique to those coaches. Many DP's have that problem because the fuel line is at a very shallow angle and diesel foams quickly and really pushes back. Yes, it's probably worse in hot weather because of the propensity to foam.

The fuel tank is located between the frame and under the floor, but the filler hose cannot be located above the tank without intruding in the house area, so RV manufacturers don't do that. That means the fill and hose run more or less flay to the tank, typically entering at the side rather than the top. This makes a rush of foam very likely indeed. About the only defense is to pump slowly if using the big truck nozzles. The smaller car diesel nozzles usually don't deliver enough fuel flow to cause a problem.

Foam pushes in all directions, so yes it will go out the other side as well. It is also at least 50/50 that the other side is a bit lower, even though the pavement may appear level.

[BFlinn181]

You said the vent line allowed into the tank when you apply air pressure, but I wonder if an internal collapse of the rubber vent line is preventing air back out. I'd try sucking air out of the vent with a shop vac to see if it works that way. Putting a piece of saran wrap over the open fuel fill with a rubber band should show if it is venting.

I first thought you meant just removing the cap caused blow back when I wrote the above. If you are talking about while fueling, if you are using a truck pump they usually have much faster fuel flow and bigger nozzles that can cause auto shut off and blow back. I've learned you have to only set trigger to the first notch and even that can be too fast for some pumps. Trucks typically fill directly into the tank, RV's often have the tank between frame rails and a longer filler neck.