Oil & Fuel Fuel cap vent

[Rockyridge]

I think that I have a problem with the vent into L3400 fuel tank.
I can run for extend period of time and the fuel gauge never seemed to go down.
I eventually checked it and there was a strong vacuum when I opened it.
Even then the fuel gauge didn’t go down but the next time that I used it the fuel gauge was right down to the empty. I filled it and everything is OK.
My guess is that the vent in the filler cap is not open as it should be fore some reason. As the fuel was used but air not allowed in, the plastic tank it collapsed from the vacuum, keeping the fuel sensor from falling and registering actual fuel level. After I opened the cap and air want back in it took some time for the tank to return to normal shape and allow the fuel sensor to return to normal operation.

This is the second time it has gone from practically full tank to nothing. The last time it happened I though the gauge was faulty because it changed so quickly until I realized that it was running out of fuel. I stop immediately, filled the tank and was able get started without having to bleed the lines. It ran rough for a few minutes but then smoothed out again OK.

Does this make any sense to anybody or do I need to go for a mental checkup?
Has this happened to anybody else?
Is anybody aware of a way to correct (clean) the fuel cap?

Thanks for any help you can provide.

 

[MOPAULY]

Makes sense to me, if the fuel tank is sucking in on itself. Have you rigged something up to cover the tank with a vent to verify if this is the problem?

 

[b_z_genius]

I have filled up 3 times so far and my tank lasts a long time before it starts to drop below full. Last week I happened to be doing some work for my parents in town and when the gage finally started to drop I drove over to the gas station and filled up, which took 3.9 gallons. I haven't noticed any suction when opening the fuel cap though. I have only had the L3400 for 2 months now but really like it and usually get about 9 to 10 hours per tank.

 

[jbrumberg]

Rockyridge:

During my first "quick read" I thought it was a bad sending unit. I have read a lot of complaints related to sending units on most of the major brand forums. On the "re-read" it lookes like you corretly analyzed the problem. I would check out that fuel cap out very carefully for debris or evidence of mud dauber wasp "nest making". I would try to clean the vent area out with compressed air if possible. I now know that I have to blow/clean out my attachment vent caps prior to use. You do not have to ask me how I now "know" this. Jay

 

[FL4400]

Try this link it might tell you more about http://www.tractorbynet.com/forums/...466-fuel-gauge-problem-l4400-psb-2007-023.pdf

 

[Rockyridge]

Thanks for the information.

I haven’t rigged anything up to verify the problem but have been opening the cap regularly and pretty much every time that I open it after running for a while I hear the sound of a vacuum in the tank.

I looked at the attached site and it looks like I am missing what they call a “white plastic piece” in their illustrations. I’ll have to see what I need to do to get a replacement. From what I’ve read on this forum, it may be unusually expensive for what you get when buying from Kubota, but if you got to have it, you got to have it.

Again, thanks for the info.

 

[N80]

Blake, did you ever figure out what was wrong with yours? Mine has always remained on Full for a long time before coming down but on this current tank it is staying on F longer than before so I'm wondering if mine is going bad too.

 

[FL4400]

George,
I have not had time to pull it apart yet, I just got back from VA this week. I have been baling hay for the last week up there helping my wife's family. But I hope to get to it in the next week or so.

 

[N80]

George,
I have not had time to pull it apart yet, I just got back from VA this week. I have been baling hay for the last week up there helping my wife's family. But I hope to get to it in the next week or so.

Keep us posted, i'm interested in seeing what you find. If mine doesn't start behaving normally I'll have to take mine aprt too. I think my warranty expires soon and this probably isn't worth renting a trailer to take it in anyway.

 

[FL4400]

I will let you know what I find out, if worst comes to worst I will call my neighbor who is a Kubota Mechanic.

 

[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.