Fuel tank collapsed

[garre1tt]

Questions: Fuel tank collapsed, has anybody had this problem or heard of it?
Can anyone see a problem using air pressure to fix this or other problems that may arise from just repairing the fuel tank?

Background story:
Just when I thought I had the problems on my 97 suburban fixed it died on my wife and would not start. I had just replaced the vacuum pump, changed the fuel filter and installed a new PMD with cooler. Ran great for two days and I thought my wife might actually like this vehicle.
After grilling my wife all I could get was,

[trbankii]

Explain "collapsed." I'm confused. Was it sucked in by vacuum? Something hit it and pushed it upward? Never heard of a fuel tank collapsing before.

[autocrosser]

Make sure you have the correct fuel filler cap. If it isn't the correct one for the diesel you can draw a vacuum on the tank and cause it to not run due and maybe in your case collapse the tank.

[Dvldog 8793]

Howdy
JC Whitney sells replacement tanks. If it was mine I would replace the tank as the collaps may have weakened things and it might happen again. Murphy would say that the next time it will be dark and raining. With the return line systam of the 6.5 and the right filler cap I would think there must be something else wrong someplace to cause the collapse.
Hope this helps...
L8r
Conley

[garre1tt]

Sorry about the description.
Yes, it was sucked in from a vacuum. We are replacing the fuel cap.

[Marty Lau]

Michael;
This sucks let me know if you need some help here in the Falls.

[JohnC]

Don't suppose it takes the same tank as a '93 standard cab PU, does it?

[garre1tt]

Thanks folks for the replies. Got the suburban back from the shop this evening. Total cost $677, $300 for the fuel sending unit. Six dollars for a new fuel cap, and the rest for labor. Not all the labor was for the fuel system problem. I had them check the IP timing and other miscellaneous tests, since it was in the shop.
They were able to use air pressure to expand the tank. This was okay for now but will always be in the back of my mind as my wife is driving our five kids around. Devil dog, thanks for the reference to JC Whitney it has been 20 years since I purchased anything there. Used to love to look through their catalog and dream of the time I would have the money to buy all I wanted. That time has not come, but I can buy what I need.
16ga SxS, called a couple times, but did not leave a message. I will try again next week. Thanks for the offer for help. John C., I am not sure about the tank match all I know is that the suburban has a 42 gallon tank.
Side note: The wife admitted today, without prompting, that she does like the way it drives. But says it is so loud. She is right, this thing pops like Cummings diesel. That doesn't bother me, except the cab noise. Did not expect that in an LT model.
Thanks again for all the inputs.

Thanks again for all the inputs.
Michael D.

[BBCB]

Michael,

When you said sending unit - did you mean the pickup tube etc? Was your lift tube bent or distorted preventing you from getting full use of your tank?

I believe this to be the case with my 97 as well - coming back from Orlando over spring break, at Marianna FL, I got the hesitation and stumble. It set the SES, then ran like it was starved for fuel. It was under 1/4 tank, and I pulled off at the first stop and when I went to remove the cap, it was under strong vacuum - you could hear a hiss and then the tank release (like a 2litre bottle, or milk jug when a dent pop's out).

After filling the truck - it ran fine the rest of the trip back to Houston, the SES went out and at each stop (meal or fuel), I opened the cap, as it continued to develop a vacuum (~75mph on cruise the entire way, 21.5mpg).

The next day in Houston, I replaced the fuel cap and fuel filter and the truck continued to run fine. This past weekend, the wife had the truck w/ just under 1/4 tank full exhibit the same symptoms, starving for fuel, but this time stalled out and would not start. When I arrived, I popped the cap - no vacumn present, but it did start, and I got it home - though it exhibited the same lack of fuel "chugging".

When I inspected the filter, the housing was only 1/2 full! After I filled the truck to 1/2 (added 10Gal), it ran fine - no problems or issues.

Two main questions are plaguing me - is the lift tube bent or distorted, is my lift pump damaged? When I opened the water drain, I get a fast drip, not a steady stream.

This next weekend, I hope to have time to drop the tank and inspect it - any suggestions from the board?

Thanks,

BBCB

[garre1tt]

BBCB,
Well, since I did not do the work myself. All I can tell you is what my mechanic told me. After it would not start, his first check was to see if the engine was getting fuel from the tank by adding some clear tubing in the line. That is when he told me I was out of fuel, and I must have a bad fuel sending unit. After I gave the OK to replace it is when he found the tank to be collapsed. He did say the pickup line was bent, but did not say how much fuel was still in the tank.
Your question made me curious, so I checked out alldatadiy.com. I found out that the pickup line has a woven plastic strainer on the end of the line. It is supposed to be self-cleaning and prevents dirt and water from entering the fuel line. If this becomes plugged, or submerged in water there is also a check valve that will allow fuel to be picked up. Due to the location of this valve, the tank should never be allowed to get below a quarter full.
Alldata had some good trouble shooting procedures for this and might be worth the look.
Hope this can be of some help and let us know how it comes out.
Michael D.

[Kidd]

Think the owner's manual says replace fuel cap every 50k or so. I change mine every year, cheap insurance. I get them for about 4 bucks at the AC Delco supplier.

K.D.

[charliepeterson]

With the summer heat coming soon and everyone knows what the heat does to these engines. The only thing keeping the injection pump cool is a fresh supply of fuel. A functioning lift pump is very important. The fuel going back to the tank is very warm and the best way for it to cool off is to mix with more fuel. You see the tank is a large heat sink. The lower the tank gets the the less the injection pump is helped out.

At work we have about 20 6.5's in every truck configuration you can have. These go back to 1995. I've replaced two injection pumps total. Yes the other maintenance is very good as well. The tanks are filled every night. I know this is almost impossible in the real world but by running with full tanks this has to carry some weight for the injection pump life.

[tanker]

Venting is a must. Withdraw product from any tank without a vent, and it will collapse. :eek: I work with petroleum and Vacuum tanks, and I've seen several petroleum tanks get sucked in from a frozen, or clogged vent, or worse case, someone replaced a vent with a plug! :confused: I have seen steel vacuum tanks corrode inside which will weaken the shell and caused them to collapse. Not a pretty sight.
So wrong cap, or bad vent in a cap can cause this. smile.gif

[DA BIG ONE]

GM diesel fuel caps on light trucks are unvented, meaning that they have no vent , or pressure releaf valve, so there must be another issue somewhere else like maybe fuel return lines, or?

On a unvented system w/unvented cap how could changing the cap reduce vacuum buildup, if the cap does not seal then there would be no vacuum buildup, am I missing something here, or?

I always get lots of vacuum hissing from my tank at fillup and it has only starved for fuel when lift pump went south.

[BobND]

I believe the caps ARE vented, but have a spring-loaded check valve that will allow a certain amount of vacuum buildup in the tank before allowing air to enter through the spring-loaded valve.

My 1984 Sub was made that way. While having starting "issues", I noticed a certain amount of vacuum buildup every time I opened the cap, so I vented the cap. No more vacuum buildup, but it didn't help may other problems, (which turned out to be a messed up fuel pickup "sock").

[JohnC]

The 6.5 fuel caps are designed to hold a couple psi of pressure but essentially no vacuum. There is a 2 way valve in the cap. The suction side valve has a light spring, so practically it takes a little vacuum to open it, but very little. Most of the time when you hear hissing upon opening the cap it is pressure bleeding off, caused by heating the air in the tank from the warm return fuel.