Collapsed Gas Tank
Thread Starter
Race Director
Joined: May 2006
Posts: 18,695
Likes: 2,572
Collapsed Gas Tank
A little over a year ago I replaced my original gas tank with a replacement from Quanta Products. The car is a November 1969 350/350. The tank I installed was a GM-33E which has the vent valve to the left of the filler neck. Last weekend I overfilled the tank while manually pouring 110 from a container. I installed the vented locking cap and hosed everything down with water. I went for a 1 hour drive and noticed the gas gauge was on 1/4. Pulled into a gas station and had difficulty removing the cap and when it did release there was a "whoosh" sound. I also discovered the tank was more than 1/2 full versus the 1/4 reading on the gauge. I had trouble reinstalling the gas cap but eventually got it on. Today I removed the gas cap, heard the "whoosh" sound again and then preceded to remove the gas door, the rubber boot around the neck and the spare tire and complete storage compartment. The neck looks like it is no longer level, tilted towards the back of the car, and the bottom of the tank looks bowed in. The gas gauge is also reading 1/4 too low.
Does anyone know how to test the vent valve on the tank, I assume it's purpose is to the prevent tank collapse?
Does anyone know how to test the vent valve on the tank, I assume it's purpose is to the prevent tank collapse?
Team Owner
Joined: Sep 2006
Posts: 31,218
Likes: 4,302
From: Westminster Maryland
Hi MW,
When the 'button valve' is functioning normally you should be able to easily depress the 'button' on the outside of the tank with your finger and it should 'return' on it's own.
The button only depresses about 1/16" or less.
Regards,
Alan
When the 'button valve' is functioning normally you should be able to easily depress the 'button' on the outside of the tank with your finger and it should 'return' on it's own.
The button only depresses about 1/16" or less.
Regards,
Alan
Thread Starter
Race Director
Joined: May 2006
Posts: 18,695
Likes: 2,572
Hi Alan:
it did move slightly when pressed but barely moved. Tank has been in the car over a year and I cant imagine anything other than valve failure causing the collapse. Hoping Quanta gives me a break on a replacement. Thanks for your reply.
Mel
it did move slightly when pressed but barely moved. Tank has been in the car over a year and I cant imagine anything other than valve failure causing the collapse. Hoping Quanta gives me a break on a replacement. Thanks for your reply.
Mel
Thread Starter
Race Director
Joined: May 2006
Posts: 18,695
Likes: 2,572
I have been using a locking gas cap for decades but just found out that for pre 1970 applications, according to a video from Ecklers, the rubber sealing ring should be removed. So my theory is the tank was overfilled, no air cushion to handle expansion, the pressure buildup of fluid caused the vent valve to seize, then the one hour drive created vacuum and the tank collapsed. Quanta was kind enough to give me a price break on another tank and I am switching to a standard vented non-locking cap.
Last edited by MelWff; Oct 25, 2016 at 12:01 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Unfortunate. The vented gas cap 'should' solve the problem. In 1970 and thereafter, the fuel vapor canister became the fuel system "vent" as the canister is open to the air on the bottom, below the activated charcoal pack. Vapors that make it into the canister get absorbed by the charcoal and later get drawn into the engine intake charge for burning (along with a bit of outside air).
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Unfortunate. The vented gas cap 'should' solve the problem. In 1970 and thereafter, the fuel vapor canister became the fuel system "vent" as the canister is open to the air on the bottom, below the activated charcoal pack. Vapors that make it into the canister get absorbed by the charcoal and later get drawn into the engine intake charge for burning (along with a bit of outside air).
I'm curious why they say to remove the seal on the cap, vented locking caps have been available for a long time. As Charlie stated above, all caps from 1970-1974 were of the vented variety and if you don't have it vented unfortunately the suction from the fuel pump will collapse the tank.
-Willcox
