Gastank Imploded!!
10-15-2007, 08:31 PM
#1
Burning Brakes
Thread Starter
Gastank Imploded!!
Bloody Hell!!
I had repaired my leaking gastank a week or so ago and it seemed to hold up pretty good. Never noticed any leaks until today.
When I went back to take a look, the entire bottom of the tank has imploded!
It looks as though it has been crushed right in but there are those tank straps, sittin' all nice and purdy and straight. I pulled the gascap and nothing happened, no hiss or suck or anything. This must have happened as I was driving. What kind of vacuum force is necessary to collapse one of these tanks?
I have never seen a tank implode like that before..........very strange?
Anyway, gastank is officially scrap, the hunt for a replacement continues.
Cheers
Bernie
I had repaired my leaking gastank a week or so ago and it seemed to hold up pretty good. Never noticed any leaks until today.
When I went back to take a look, the entire bottom of the tank has imploded!
It looks as though it has been crushed right in but there are those tank straps, sittin' all nice and purdy and straight. I pulled the gascap and nothing happened, no hiss or suck or anything. This must have happened as I was driving. What kind of vacuum force is necessary to collapse one of these tanks?
I have never seen a tank implode like that before..........very strange?
Anyway, gastank is officially scrap, the hunt for a replacement continues.
Cheers
Bernie
10-15-2007, 08:51 PM
#2
You have a blocked vent which is supposed to inhale not exhale and the fuel pump collapsed the tank. The pump makes what 50 lbs of fuel pressure which it removes from the tank so 50 lbs per square inch of suction is more than enough to make your gas tank look like a prune !
10-15-2007, 08:58 PM
#4
Burning Brakes
Thread Starter
Kinda figured it was something like that but how odd that it would come right on the heels of a leak repair? Murphy's Law I guess.......
Someone telling me to replace the damn thing.
Can the tank be dropped without having the car on a lift?
I have pretty good jack stands to get the rear up.
Gotta go drain gas again!
B2
Someone telling me to replace the damn thing.
Can the tank be dropped without having the car on a lift?
I have pretty good jack stands to get the rear up.
Gotta go drain gas again!
B2
10-15-2007, 09:18 PM
#5
Bernie,
Did you have problems filling the tank with fuel after the repair, as this would have been the first indication of a blocked vent pipe? This vent pipe passes throught the sub frame up to the filling pipe and is a very good tight fit through the subframe. It can be eaisly crimped if the tank is removed or repositioning after a repair. On reinstallation of the tank I have found the best method to avoid crimping the vent pipe is to spray the vent pipe externally and the internal of the hole through the subframe with WD 40.
As the tank is a plastic material it would be very easy to implode with a small vacuum. A full vacuum is equal approximately 32 inches of mercury which equales 1 atmoshpere and is equal to 14.70 lbs/sq inch pressure. The fuel pump fitted to 928s are quite capable of reducing the pressure sufficiently to cause an implosion of the fuel tank.
I have seen very large steel tanks implode due to a vacuum.
Tails 1990 928S4 Auto
Did you have problems filling the tank with fuel after the repair, as this would have been the first indication of a blocked vent pipe? This vent pipe passes throught the sub frame up to the filling pipe and is a very good tight fit through the subframe. It can be eaisly crimped if the tank is removed or repositioning after a repair. On reinstallation of the tank I have found the best method to avoid crimping the vent pipe is to spray the vent pipe externally and the internal of the hole through the subframe with WD 40.
As the tank is a plastic material it would be very easy to implode with a small vacuum. A full vacuum is equal approximately 32 inches of mercury which equales 1 atmoshpere and is equal to 14.70 lbs/sq inch pressure. The fuel pump fitted to 928s are quite capable of reducing the pressure sufficiently to cause an implosion of the fuel tank.
I have seen very large steel tanks implode due to a vacuum.
Tails 1990 928S4 Auto
10-15-2007, 09:23 PM
#6
Nordschleife Master
Kinda figured it was something like that but how odd that it would come right on the heels of a leak repair? Murphy's Law I guess.......
Someone telling me to replace the damn thing.
Can the tank be dropped without having the car on a lift?
I have pretty good jack stands to get the rear up.
Gotta go drain gas again!
B2
Someone telling me to replace the damn thing.
Can the tank be dropped without having the car on a lift?
I have pretty good jack stands to get the rear up.
Gotta go drain gas again!
B2
Things to check:
1. Fittings on the expansion tank aren't blocked
2. Check-valve on the front side of the expansion tank is working (and fitted the right way around)
3. Charcoal canister in the front-right wheel well is connected up and not blocked.
4. The hard line that comes down behind the back bumper isn't blocked (the final ventilation point - links to charcoal canister and is open to the air)
You can get the tank out with the car up on stands.. I dropped mine a couple of weeks ago and replaced all the hoses, including the return hose on top of the tank that can only be done without the tank in the car (its about 8 inches of 3/8 fuel hose.. cheap to replace).
Getting the tank back in is a bit fiddly.. but doable on your own.
Read these handy pages:
http://www.kondratyev.com/porsche/te...ngine/tank.htm
http://members.rennlist.com/sharkski...0-FuelTank.htm
10-15-2007, 09:24 PM
#7
Chronic Tool Dropper
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You have a blocked vent which is supposed to inhale not exhale and the fuel pump collapsed the tank. The pump makes what 50 lbs of fuel pressure which it removes from the tank so 50 lbs per square inch of suction is more than enough to make your gas tank look like a prune !
Ummmm, not quite.
The pressure on the tank will never be more than atmospheric on the outside (14.7 PSIA at sea level), and the lowest it will ever be inside is the vapor pressure of the fuel (depends on local fuel composition and temperature). You are correct that it was probably a plugged vent, but the "50 lbs of suction" just can't happen.
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10-15-2007, 09:27 PM
#8
Nordschleife Master
Did you have problems filling the tank with fuel after the repair, as this would have been the first indication of a blocked vent pipe? This vent pipe passes throught the sub frame up to the filling pipe and is a very good tight fit through the subframe. It can be eaisly crimped if the tank is removed or repositioning after a repair. On reinstallation of the tank I have found the best method to avoid crimping the vent pipe is to spray the vent pipe externally and the internal of the hole through the subframe with WD 40.
It attaches right next to the ventilation line (just behind the filler cap), and at the top of the main part of the tank, forming a loop on the tank itself.
10-15-2007, 09:36 PM
#9
Burning Brakes
Thread Starter
The tank was not removed to repair the leak and it couldn't have been equalizing the pressure before the fix because the repair is on the side of the tank towards the bottom. If there was air getting in, there was fuel getting out.
All fingers do point towards a blocked vent though as that seems to be the only way this could have happened.
I don't plan on repairing it again as I see this as a sign to change the damn thing and be done with it.
Getting ready to drop the tank tonight.
Any words of wisdom on dropping this thing?
Thanx for the help so far
Bernie
All fingers do point towards a blocked vent though as that seems to be the only way this could have happened.
I don't plan on repairing it again as I see this as a sign to change the damn thing and be done with it.
Getting ready to drop the tank tonight.
Any words of wisdom on dropping this thing?
Thanx for the help so far
Bernie
10-15-2007, 10:05 PM
#10
Chronic Tool Dropper
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Take the gas out first.
Disconnect everything, including the sender through the luggage area, lines to/from the engine bay. The tank is amazingly light when it's empty out on the floor, amazingly heavy as you wrestle it in and out.
Take a look at PET to see all the connections. Your new tank will be by far the best guide to what needs attention.
No smoking of course.
10-15-2007, 10:41 PM
#11
Burning Brakes
Thread Starter
Take the gas out first.
Disconnect everything, including the sender through the luggage area, lines to/from the engine bay. The tank is amazingly light when it's empty out on the floor, amazingly heavy as you wrestle it in and out.
Take a look at PET to see all the connections. Your new tank will be by far the best guide to what needs attention.
No smoking of course.
Disconnect everything, including the sender through the luggage area, lines to/from the engine bay. The tank is amazingly light when it's empty out on the floor, amazingly heavy as you wrestle it in and out.
Take a look at PET to see all the connections. Your new tank will be by far the best guide to what needs attention.
No smoking of course.
Wisdom indeed!
Thanks DocB
Bernie
Hey, I'm a member again.....................uh-oh!
10-16-2007, 01:20 AM
#12
Burning Brakes
Thread Starter
Well,
I got the tank out.
It wasn't all that difficult actually.
I ran into 2 clamps that were completely seized and not going anywhere. I opted to just cut the hoses and get the thing out of there. They were the two lines branching off from the "T" fitting on the filler neck. One goes to the expansion tank and the other is a return to the main tank. That line got me as I wasn't aware at first that it runs through the body. Once I pushed the line through, the rest was easy.
Getting the tank out wasn't a big deal. Drop the tank down some and then twist it towards the driverside of the car. It has to clear the rear suspension on the passenger side so thats why it needs to make a twist. After that, it popped right out. I paid particular attention to this to be sure I had my technique down for putting in the replacement.
I still need to investigate the vacuum issue inside the tank though.
Thanx for the help fellas.
Cheers
Bernie
I got the tank out.
It wasn't all that difficult actually.
I ran into 2 clamps that were completely seized and not going anywhere. I opted to just cut the hoses and get the thing out of there. They were the two lines branching off from the "T" fitting on the filler neck. One goes to the expansion tank and the other is a return to the main tank. That line got me as I wasn't aware at first that it runs through the body. Once I pushed the line through, the rest was easy.
Getting the tank out wasn't a big deal. Drop the tank down some and then twist it towards the driverside of the car. It has to clear the rear suspension on the passenger side so thats why it needs to make a twist. After that, it popped right out. I paid particular attention to this to be sure I had my technique down for putting in the replacement.
I still need to investigate the vacuum issue inside the tank though.
Thanx for the help fellas.
Cheers
Bernie