Oil & Fuel Fuel Cap Problem

[zmansmac]

I am a new and proud B7500 owner. The second time I started to cut grass my tractor stalled. I had a hard time trying to start her and, even though the fuel guage showed full, decided to add more fuel. I did this because I thought there was an outside chance that the fuel guage was not working properly and I may have actually run dry. I also had no idea of fuel economy with this tractor as it is my first diesel. /forums/images/graemlins/crazy.gif She had 7.7 hours at this time. I topped off the tank; it took 2 1/2 gallons. Since the B7500 has a 5 gallon tank I figured low fuel was not the problem. The tractor started up after that and I finished cutting the grass without any problems. At this point I was concerned that my tractor had some kind of intermittent problem. A couple days later I was using the FEL to move a little dirt and the tractor stalled again. /forums/images/graemlins/mad.gif I got her to start but she wouldn't stay running so I left her alone for about a half an hour. She then cranked a while and started so I moved her into the pole barn as quickly as I could. Another problem I noticed was the fuel inlet was no longer centered in the hole in the hood. I figured that because my lawn is a bit bumpy the tank must not have been tightened down and shifted position. Two days later I decided to at least try and correct the tank inlet problem. By this time the inlet was shifted over so badly I had to open the hood to remove the cap. When I did a tremendous air rushing noise was heard. This is when I realized that part of my problem was that the cap was not venting. I took the cap back to my dealer who cheerfully exchanged it. /forums/images/graemlins/grin.gif Getting back to my tank readjustment I realized that I had to remove the instrument panel to gain access to the mounting bolts. Imagine my surprise when I discovered that the back end of the tank was severly distorted from being sucked in. See attached picture. Everything became clear to me at this time. You'll notice in the picture that the fuel guage sending unit location is distorted to the point where it was stuck in the "full" position. And the first time the tractor stalled out on me - it was out of fuel. The tank was sucked in so badly that it's capacity was reduced to 2 and 1/2 gallons. And the tank was also empty the second time she stalled on me. I called my friendly dealer who agreed to pick up the tractor and replace the tank if necessary. Problem was the grass needed cutting again and I was afraid to let my new "baby" go away for a while. Since I have some mechanical experience I thought I'd see what I could do correct the problem. There are 3 hoses connected to the tank. 2 smaller ones for injector rail and fuel pump returns and a larger hose at the bottom for fuel pump input. I removed and plugged the 2 small hose connections. I then removed the fuel pump hose at it's inlet and held an air compressor blow gun to the hose with the pressure set at 20 PSI. This did nothing and I had to slowly raise the pressure to about 80 PSI before I heard the first "pop" of the tank expanding back into shape. A couple more "hits" of air and pops later the tank was back to normal. This also put my fill inlet back in center with the hole in the hood. The gas gauge works great now. /forums/images/graemlins/laugh.gif The other problem I didn't mention earlier is that the engine was taking longer to start. This was because of the vacuum condition and now with a new cap the engine fires instantly after a couple seconds of glowing. Obviously my fuel cap was bad from the start and hopefully this is just an isolated incident. But if Kubota got a bad batch of caps others new owners may be experiencing problems like this.

I hope I didn't get to wordy for all you reading this post; I'm still new at this. I have learned a lot from reading other posts on this forum and hope to be able to contribute as well myself.

 

[GregJ]

Thanks for the post. Hopefully that will be an isolated incident for you. I have about 200 hard hours now on my B7500 now and really haven't had a problem. I appreciate hearing about any potential problems and solutions. It's amazing how much grief a simple little part like a fuel cap can give.

Greg

 

[Jeff396]

Zmansmac,

I don't think there was anything wrong with your fuel cap. Those oval holes aren't supposed to be the vents. It would be impossible to cast something like that in one piece and still be able to remove it from the mold.

Yesterday when removing my fuel cap the rubber diaphram came off. When I looked closer I noticed a hard plastic washer the same size as the tank opening that sits underneath the diaphram. In this plastic washer there are cut two wide shallow depressions preventing the rubber diaphram from sealing completely. It sounds as if you traded in your old cap but I wonder if yours was missing that part.

Jeff

 

[zmansmac]

Jeff,

You may be right. Although it is amazing what they can do these days with plastic molds. You are correct that I traded the cap in to my dealer for a new one and no longer have it. I had a copy of the parts manual while I still had my old cap and saw in it that there is supposed to be some kind of rubber or plastic washer between the inside of the cap and the diaphram. I did check to make sure that part was there although I did not remove it from the cap or inspect it close enough to see if it had the depressions you're talking about. That could very well have been the problem. Thanks for the information. I will take a look at my new cap and check it out.

JohnZ

 

[Anonymous Poster]

I guess I have a question if the vent for the tank is provided by the cap. I have so far overfilled my 7800 twice and the overflow is directed out an overflow hose that runs to the left of the engine cowling. I would think that this line would double as a vent since it is connected to the tank. Any feedback on this?

Thanks,

Frnak D.

 

[Chief]

Wow! Now that is what I call a strong pump! I think you may have that high performance suction pump.......... it is called the Monica pump option. /forums/images/graemlins/wink.gif Those Monica's seem to stir up trouble no matter where they go! /forums/images/graemlins/smirk.gif Glad you were able to get the problem fixed.

 

[Jeff396]

On my B7500 the fuel overflow tube is not connected internally to the tank. It is connected to a cup that is around and below the cap to catch any fuel overflow. I'm not sure if they do it the same way on the B7800. I would also think that if they used a simple rubber hose to vent the tank that they might also need to have a filter to prevent that wonderful dust our rigs create from entering the tank. The baffle under the cap has a very limited area for air entry and in addition the rubber diaphram has a bunch of ringed chambers to help prevent dust from getting in.

Jeff

 

[Egon]

I'd have the fuel tank replaced. There may residual stress from the distortion that may come back to haunt you after the warranty has expired.

Egon

 

[Pks]

That is exactly what I was thinking. Without knowing, a crack could develop in a year or two...

IMHO, I really think it's worth the effort to get it replaced under warranty now.