Opelotus

First some background info: the steel vapor line running from the fuel system expansion tank to the evap canister had rusted out (US '84) Since the rest of the evap system was trash (dirt was getting into intake thru a broken Y connector, and vacuum control valves are all busted) I removed the line + rest of system and capped the expansion tank's rubber hose just after the rollover valve until I can find a better solution. Well this doesn't work out because with the air temp outside getting lower and lower and no ventilation in the tank, the bottom of the fuel tank has been sucked up into itself so I can see the fuel pump and filter when it should be hidden. I opened the fuel filler cap so it can vent and hopefully return to normal. What can I do to stop this? Replace the line that runs to the evap canister so the system can vent?

blown 87

Why don't you just repair the EVAP system?
Seems like the best course of action .

Rob Edwards

Agreed with Greg, they don't collapse if they're properly vented. I doubt the air temp has anything to do with its implosion, the lack of ventilation is 100% at fault.

I doubt it'll pop back into shape by itself, and I'd be very careful about getting it back into shape while it's cold outside- the last thing you want to do is crack and ruin the tank. Maybe drain it as much as possible (pull the short hose off the internal fuel pump to drain, or siphon out the top) , then hit it with a hairdryer or radiant heater (stick the car out in the driveway so you don't win a Darwin award), remove the level sender and push the tank back out with a tennis ball on a curtain rod.

BIG 928

i had this happen on a gts i took the pump cover off to feel if the pump was working as the car wouldnt start. i realised i could put my hand all around the pump and i shouldnt of been able to. the pipe to the evap/ charcoal canister was blocked. id fix the system, i have removed all of the pipes etc and put a pipe up in the air with a valve in to allow fumes out but no petrol as iits on a race car to reduce the weight. if the tank cant breath it will suck in, its unbelievable that the fuel pump has that much strength.

ragards mark

Opelotus

Since the car is 25+ years old I don't need to go through emissions in CT, so I don't want to spend money on fixing the system while it isn't all that necessary. The fresh air line that runs from the back bumper to the charcoal canister is still in good shape, so what if I run a new line from expansion tank to canister, then just connect canister to the fresh air line for venting?

What kind of valve did you use on the racer?

BIG 928

i returned the tank back to shape after draining the fuel by sealing all holes, heating the tank and blowing back into shape with compressed air.

regards mark

Landseer

I had one collapse pretty far. I left it sit for a week in the sun and it rebounded.

How does the vent system work? Isn't there also a filler neck vent.

BTW, this is one of the few corrosion points on these cars. Two of mine from MA rusted out. NAPA sells some lengths of hard gasline you can use, along with a tubing bender. Combined with some low pressure fuel line and clamps you can replace it pretty easily.

polecat702

Rob and Greg are both correct. I think Rob and I had the same problem last summer with our fuel tanks.
I would do as suggested, drain the tank, flush with some diesel fuel, and I used Rob's compressed air solution to pop my tank back into shape. I believe Rob had a video posted, that showed how he did it.

My tank imploded due to a pinched vent line at the cannister. Search is your friend.

Rob Edwards

Here's my thread on the subject, I had a solenoid valve fail and constant exposure to intake manifold vacuum collapsed mine despite all the vent lines being open.

There are some pics of the arrangement of the undercar lines in the link:

https://rennlist.com/forums/928-foru...el-sender.html

BIG 928

it has 8mm or 10mm push on fittings it has a ball bearing in or something, i got it from a company called demon tweeks in the uk they have a online catalogue, there are pictures on there, ill get the correct name of it tommorow. it cured the problem i had when i removed all the canisters pipes etc, i had fuel coming up the breather pipe at the start of a hour race if the tank was full when cornering hard, i also use one on a 993 gt2 race car as this car has to run a full tank for 35 minute races as it only holds 60 litres and the car is very thirsty. its a good little valve, ive got to go now, ill sort the name of the valve as soon as possible tommorow.

regards mark

Mrmerlin

please whats the year of the car your working on?

Jadz928

This happened to me for similar reasons, though my intent was completely different - LINK to thread
I wouldn't gut a functional system just because you think it is unnecessary.

The gas cap doesn't vent when seated all the way. There is a "T" in the evap system in the neck, though.

Why diesel fuel?

polecat702

If as Rob suggested to use a radiant heater, or hairdrier, the vapors won't ignite like gasoline. It's safer, and diesel will not hurt the fuel system.

Opelotus

"I wouldn't gut a functional system just because you think it is unnecessary."

- I didn't really gut a functional system, I tested all the vacuum control valves and they were leaking badly (didn't test thermo valve though), plus filled with dirt from the broken y-connector in the wheel well, and the hose leading to the throttle housing was clogged solid with dirty oily junk. So none of it was working properly.

- Car is a US 1984 (stated in first post).

- I left the fuel cap loose overnight and the tank returned to its normal shape! Still off by a fraction of an inch but I'm not worried.

Landseer: as far as replacing the vent line, does Napa also sell plastic lines like what is found on most never vehicles? I'm wondering if that would be a better alternative...unless there is too much heat in some areas under the car.

Also - until I decide how to properly vent the tank, what can I do to prevent it from collapsing again without having to smell fuel vapors all the time?