Please take a look at the two pictures of the bottom of my '96 Blazer LS fuel tank. The bottom of the tank is concave. Is this how they all look or is mine imploding? When I fill up my 18 gallon tank it only takes 13.5 gallons. It did sit idle for 5 years. If this is not how they are supposed to look, perhaps a vacuum was created that sucked it in.

 

Yeah, I dont think its supposed to look like that.

 

Nope...tank should not have that concave area. Almost looks like some one put a floor jack on the tank. Would think that this would reduce the volume by much, but perhaps the concave area is larger than the picture really shows.

Only way I can think of to fix this would be to remove tank and press the area out. I think one could get an arm into this area, perhaps a piece of wood or something to press it out....may be air pressure.

Be careful dropping the tank as there are two plastic vents attached to rubber hose; one is at the very front of the tank, difficult to get to until tank is down a bit.

Good luck.

 

Like Lanny said, might be from jack, or it almost looks like someone just went to town with an impact on the gas tank strap connection.

 

I appreciate knowing that this concavity not normal. I also have a leaking fuel pump check valve, so two birds with one stoe. It's good to know there is some hope of pushing the tank back out. If either of you knows how to remove the 3 hoses from the fuel module, that would help a lot. I pushed a nail under the tab on one of the 3 and lifted the tab up to clear the flange on the fuel module nipple, but the hose would not come off. I'm wondering if there is another tab on the other side of the same hose that I cannot see or whether there is something besides the tab to deal with.

 

I had a Jeep several years ago that the exact same thing happened. I replaced the tank and within a few weeks, my new tank was also caved in. Then I knew that something more was happening and started to investigate.


I had a plugged vent line to tank that would not allow air into the tank to replace the volume of fuel used. The longer I drove it, the worse it got until I eventually had only about 1/2 my original capacity. Whenever I stopped for fuel, and removed the gas cap, there would be a very noticeable air sucking sound.


Check all of the vent lines for the fuel system and make certain they are not plugged, kinked, or otherwise restricting the passage of air into the tank.

 

I had a sports car with a similar problem, except it was a 1967 model. Had a locking gas cap and went through 3 gas tanks until I found the cause. It died on me on a stretch of road that didn't have any lights and it was close to 11 pm. Only thing I had for light was one of those sticks you have in a first aid kit that you shake and they glow. Car died, I cussed, opened hood and pulled feed line of fuel pump and heard it sucking air. Realized that replacement tanks were vented type and cap was not. So it would create a vacuum in tank. I loosened the gas cap and started engine and drove home. Next day drilled a 1/8 hole in filler pipe and put a pop rivet in it. Never had any more problems.

 

I just did my Fuel Pump this morning. (4 hours) If it is the same as the 2002, the two outside hoses have the same setup; there is a tab on both sides of the connector that have to be pressed in then pull the hose out. I was able to pinch one, **** the connector, then pinch the other and pull it out. the middle one is different, it has lie a plastic band around it, pinch those.
The rubber gas fill is a clamp but there is another venting hose on there too, that one comes off by pushing it to one side to relieve the one grippy nub. What a pain, 3 hours to figure out how to disconnect 8 connections, 1 hour to put it all back together. I miss the old two hose tanks of yesteryear. Gas Fill, and hose to Mechanical fuel pump up at the engine.

 

EdC, I am trying to understand in general how this tank venting works to discover why my tank imploded. I realize that your '67 may not directly apply to a '96 California vehicle in which the Engine Control Module may actually create a vacuum in the tank intentionally during the evaporative emissions test.

You were driving so fuel was being pumped out of the tank which would tend to create a vacuum in the tank. If the "tanks were vented type", why didn't the vent allow air in to fill the vacuum?

 

No kidding: what a pain. I wish I had heard from you several days ago. Like you, I figured out that all three connectors have to be squeezed hard and then pulled off the hose while squeezing. It's very hard to get a squeezing hand and a pulling hand in that restricted space at the same time.

I was unable to budge either hose connecting the tank to the filler tube or the filler vent with a pipe wrench. I ended up sawing through the hoses with a hack saw. If this happens to any readers, here is where you can get new hose: Fuel Filler Necks & Gas Tank Pipes | Filler Neck Supply Co. I believe they advertise on the Blazerforum.