We stopped for fuel twice on our trip to bring our new-to-us coach home. But we... actually, I was not totally versed on the idiosyncrasies of the fuel system. Like, I didn't know you couldn't trust the gauges, you must burp it while feeding the tanks, and the back and forth sharing of fuel between the tanks.

I had my first real experience with a full fuel stop Friday afternoon at a Costco. It took a full 15 minutes to pump 28 gallons of gas into my tanks. I used the first pump so I didn't block a second pump and motioned cars behind me around when the forward pump opened up. (6-7 times) One good part was the number of guys that came over and commented on our baby and remembering a time when...

I would be interested in any solutions people have come up with to help with filling these things easier.

We stopped for fuel twice on our trip to bring our new-to-us coach home. But we... actually, I was not totally versed on the idiosyncrasies of the fuel system. Like, I didn't know you couldn't trust the gauges, you must burp it while feeding the tanks, and the back and forth sharing of fuel between the tanks.

I had my first real experience with a full fuel stop Friday afternoon at a Costco. It took a full 15 minutes to pump 28 gallons of gas into my tanks. I used the first pump so I didn't block a second pump and motioned cars behind me around when the forward pump opened up. (6-7 times) One good part was the number of guys that came over and commented on our baby and remembering a time when...

I would be interested in any solutions people have come up with to help with filling these things easier.

This is not a treatise on a British mid-afternoon custom.

It is about the GMC Fuel System.

All the coaches were fit with two fuel tanks that have common fill and fill vents Teed together under the coach. The fill vent is the other 3/8 line that comes out of the sending unit. The T that is the subject of this is near the forward end of the auxiliary (front) fuel tank. This is a design disaster with the modern foaming fuel. I have been fighting this for six years and gotten quite tired of the whole affair.

When I redid the fuel plumbing, I carried both fill vent lines as far forward and upward as was practical. That turned out to be just under the cab floor where the fill line doglegs around the wheel well. The end result is that the last three times I have fueled, the fill when so well and so fast that it was disconcerting. I can fuel at the pump's full rate until shut off.

This can possibly only be appreciated by a few, but I actually took an old software package (purloined from an employer when the package was upgraded) and ran an less than complete model of the fuel system when filling. This was very fortunate. I learned two things. First was that the fix that I had in mind would probably not have done any good at all and it would be complex and expensive. The second was that, because the rear (main) tank actually fills first (with little regard to vehicle trim (ride height front to back), it will always flood the vent line if given the opportunity. If that flooded vent line is still needed to vent the auxiliary (front) tank, you are SOL (Second On Line) for the only fast fill.

This was no great difficulty in my case because I already had the entire fuel system apart and all over the barn floor. For a normal rational person or even a GMC owner, it would still not be all that difficult. The good thing is that the hardest part is not all that much of a problem. That is taking down the entire fill pipe.

I don't suggest that you do this a a primary operation. but next time you are replacing all that leaking rubber house with new, think about adding this feature.

Matt

James Hupy wrote on Mon, 30 July 2012 14:41
What frequently happens on the GMC coaches as they age, the body to frame mounting pads compress and pinch the vent lines to the charcoal cannister.
When those passages can no longer handle the volume of air that is displaced when we fill our tanks with "reformulated gasoline". the displaced air tries to find it's way out via the fill pipe. What happens then is what many of us experience. Frequent clicking off and gasoline burping back up the filler neck. Tank venting is important. The cure is to replace the frame cushions, as well as careful routing of the vent lines.

Jim Hupy

Jim is close, but he is a little wrong. The fill vent goes along the fill line and to the fill neck. Look in the MM figure 8-3. That T in the vent line is most of our problem. The vapor valve and carbon canisters are only there to pass the old time evaporative emissions and to be the air vent when fuel is drawn from the tanks other wise a vented fill cap would do just fine.

Matt

I found, even after updating my tanks and adding second vent, dropping the right rear airbag helps tremendously