Oil & Fuel Fuel cap vent

[Kevin Beitz]

I would say the vac in the tank would also suck the air out of the cork sending unit and when you open the tank gas then would be sucked into the cork float making it heavy then you would need a new sending unit...

 

[Chessie]

This is not just limited to the L series. My 2005 B 3030HSDC was doing the same thing. I was unaware of the suction until I went to start the unit and it wouldn't start because the vacuum from the fuel tank sucked the fuel out of everything once the engine was turned off. I just learned not to really tighten down too much on the fuel cap and have not had the problem since.

I do not see any small hole in the fuel cap to permit venting of any type. Anybody know where the hole in the cap should be??? I was thinking of putting a #80 drill bit sized hole on the side of the fuel cap to aid in the releif effort.
Jeff

 

[FL4400]

Chessie the cap on the L4400 has same hole all the way around the lip of the cap, it seems like it should be that way on all the caps.

 

[zmansmac]

I'm not sure what fuel cap you have but it may be the same as the one on my B7500. There are little rectangular vent holes all around the outside of the cap. I bought mine new 4 years ago. Never having owned a diesel powered anything before all I knew was that they were more efficient. After cutting grass a couple of times and not seeing the fuel guage move much I became suspicious. Shortly after the engine started to loose power. I opened the cap but could not see the fuel level because of the neck design. I do remember a slight whoosh or air but the old brain cells didn't trigger on that clue. Everything was OK but only for a while. It turned out that the original cap was not venting and as fuel was being used the vacuum was sucking in the 5 gallon plastic tank to the point where the fuel guage pickup was "stuck" in a relatively high position. I took the cap to my dealer along with pictures of the collapsed tank and he promptly gave me a replacement cap. I would have had the dealer replace the tank but I figured that would take several weeks and I didn't want my new baby gone that long. So I very, very carefully applied low air pressure to the input fuel line which popped the tank back into original shape. I, of course, had to do this with the faulty cap before I turned it in. Here are before and after pics. Bottom line is that, although rare, vented caps can be faulty or fail and getting dirty.