Gas fumes? Tank leaks? Read this.

[Neil - Colorado]

Thank you Dean924s!

I would like to make a comment on the removal of the "Two-Way" valve or "Overfill Limiter" as it is sometimes called.

This valve allows pressure to escape to the charcoal canister when the tank reaches a predetermined pressure. It also allows air to enter the tank if a predetermined vacuum exists. This is where the "Two-Way" comes from.

The valve is there to force a small air space to exist above the liquid level when the tank is topped-off during refueling. If you look into the filler neck of a removed tank, you will see that it extends somewhat into the tank. The bottom of the neck determines the effective liquid level.

Removing this valve would certainly eliminate the pressure buildup inside the tank, but it would also allow the liquid level to rise to the point where it enters the vapor lines.

Perhaps Porsche should have provided a valve that releases at a lower pressure!

Cheers!
Neil

[Granite 944]

So, it would seem, that if one is getting any serious amount of pressure build-up inside their tank, or if they may think this, then the most logical place to go look, and or part to suspect would be the charcoal canister being plugged up, and NOT go after this valve FIRST. When was the last time YOUR charcoal canister was replaced? I STILL haven't replaced any of the ones on my cars! Maybe I should!

I still haven't gotten the replacement tank installed yet. Its ready though!

[Neil - Colorado]

Granite944:

If one suspects the vent line to the canister, or the canister itself is clogged, there is an easy way to check this. Simply disconnect the line where shown below and blow into the tube going toward the front of the car. It should flow freely as mine does. Chances are, that this will check-out ok.

My 23 year old daily driver still has the original canister installed, and I have never had any gas fume problems. Actually no problems period!

I am considering installing a 2-way valve that releases at a lower pressure than the Porsche's unit. The one in my Montero seems to be a good choice. Plus, one can be plucked easily from the boneyard since it is mounted under the left rear fender well.

Neil

[3D914]

I recently replaced the cracked plastic tube that resides on the the top of the tank. THat were my vapor leal was coming from. I also updated all hoses.

Now I get good pressure that is noticable when I stop to get gas. However, Is this pressure supposed to be maintained for some period of time?

If my car sits in the garage for a while and I check the cap - no more pressure. This concerns me since I have still beeen getting faint vapor smells - nothing like what it was before - but its still there.

Any ideas?

[Neil - Colorado]

Hi Gerard:

I'll update by explaining a modifiaction that I made since my last post. I had mentioned that Porsche probably should have provided a 2-way valve that releases at a lower pressure. Well, I replaced the Porsche-supplied valve with one that is standard to a first-generation Mitsubishi Montero. Owning one of these vehicles, I was able to compare the release pressures of the two valves. Also the Mitsu valve is easy access (and source from a junk yard). The photos below show the replacement of the Porsche valve (black) with the Mitsubishi valve (blue).

The Mitsubishi valve provides the same air space when filling the tank, yet does not allow such a high pressure build-up during driving or hot weather. When I remove the gas cap, I usually hear a slight release of pressure instead of the high pressure rush and creaking noises from the relaxing tank. With my current set-up I have absolutely no fume problems AT ALL.

To address your question concerning the release of pressure over time; in addition to the 2-way valve's pre-set pressure release mechanism, it has a tiny orifice in the diaphragm that allows pressure to release over time. So, even if all components are sealed tight, the pressure will eventually disipate.

Gerard, were you able pressure test your fuel tank while replacing the vapour lines?

Best regards,
Neil

[JonA]

A little piece of 100% cotton from an old tee shirt saturated and bonded with two part marine epoxy (West System). Worked for two years and maybe more, I sold the car. I cut an access panel in the bottom of the trunk to do the work and for periodic inspections.
Let us know about the plastic tanks, that's the best solution yet.

Jon

[3D914]

Neil,

The tank was pressure-tested when it was out. All was sound except for the plastic runner that sits on top. We simply replaced it with one continuous piece of hose from the tank to the filler neck.

The ball-valve appeared to function properly, but not sure about the pressure-relief valve you're describing.

I have yet to trace the tubing to the charcoal canister, so that will be my next task. I may find something there.

THanks,

[Neil - Colorado]

Gerard:
It sounds like you solved the difficult-to-access problem. At least you won't have to drop the tank again!

Jon:
I found that the later plastic tank is a no-go in our cars. The structural cross member does not allow the installation.

Having the tank soldered and reducing the pressure with the Mitsubishi valve has made all the difference. I haven't given the fume problem a thought in quite a while. Now, If I could solve the howling ring and pinion...

[3D914]

Neil,

Can you elaborate on the "howling ring & pinion"?

I noticed that since I re-installed the tranny that I'm getting a high-pitch noise in the back. It only makes noise during constant load, not during deceleration. I thought it might be a bearing, but I haven't pursued it yet.

[Neil - Colorado]

Hey Gerard:

I'll shoot you a Private Message on that topic.

Neil

[galwaytt]

sorry to drag this up again but...........what if you've got a 968 with the gas/petrol smell !!!

Being a RoW car, it doesn't have the charcoal canister, so that's out..........

any ideas?

[nynor]

i'll take it off of your hands and save you the problem of fixing it for $500.

but seriously, why wouldn't it have the charcoal canister?

[Schumi]

I believe I have this problem on my one '87 924S. Only the leak seems to come down the side of the tank on the passenger side, away from the exhaust. It only occurs when the tank is full. I have yet to see if this also happened to the tank on my other '87 924S but I may be pulling the transaxle early next spring and will drop the tank to inspect it when I do so.

[JonA]

One painful lesson that I learned from a problem with the gas tank on my boat, Methanol which supplements the gasoline in many states is a universal solvent. It will dissolve epoxy and probably some of the other goos used to patch your tank. Metal patches, soldered or brazed into place seem to be the only way to go if you are considering a repair.

Jon

[SolReaver]

Hey guys. great thread. It actually encouraged me to drop my gas tank while I was doing my clutch. I also have an 87 924S. I inspected the tank and found no cracks at all! not believing that something would go right with this car I pressure tested the tank. A-OK. Wow. So, I replaced the lines while I had the tank down. I figured 20 something years is good to get out of a set of lines.

As the tank was not broken, I decided not to fix it. I still have the snake nest open on the wheelwell and am looking for a 2 way to replace my 2 one-ways of which we have 50% function. If you can give me a year and perhaps a part # I could probably order it.

Again, thanks 4 the awesome info

[Rasta Monsta]

Originally Posted by Schumi

I believe I have this problem on my one '87 924S. Only the leak seems to come down the side of the tank on the passenger side, away from the exhaust. It only occurs when the tank is full. I have yet to see if this also happened to the tank on my other '87 924S but I may be pulling the transaxle early next spring and will drop the tank to inspect it when I do so.

Schumi, did you fix this? My S had the same problem, and it was the dumb-arse plastic tube ("fuel expansion chamber," around $80 here) that cracked and was leaking. Don't be shy about the job, I had the gearbox on the ground in an hour and the tank in another hour.

Any opinions about deleting this part, and replacing with hose, as the poster above did?

Also, any opinions about German style braid-covered hose vs. plain rubber for this application?

TIA


rasta

[Schumi]

Rasta-

I stopped noticing the problem a while back and only drive the car once a month nowadays.
I haven't filled the tank up more than 1/2 way in a long time since it doesn't get driven; no use letting a full tank of gas sit for a long time.

[John_AZ]

This is one of my most often "linked" sites for gas fumes. Very well done.

I just had my 1987 924S tank brazed/welded in April. My cost for a HD repair was $100. The shop owner was not convinced that just patching the cracks would prevent a new crack to develop and put a BIG patch over the entire area. Maybe overkill but it made sense to me. The frame is not very rigid. If you jack the car from one back wheel and try to open the rear hatch, The hatch pins bind on my car.

To weld the tank the fuel tank strainer is removed. My screen had cracks in the mesh and would allow setiment and stuff to get into the fuel pump.



I replaced the mesh screen from Pelican-$45

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=928-201-081-04-OEM&catalog_description=Fuel%20Tank%20Strainer%20%20

Other members have posted you can cut the tank to pump line and put in a Chevy inline filter.

I also repaired my dash fuel guage by cleaning the sending unit with these instructions.

http://www.924.org/techsection/technical.htm Yours may be different. Have a new fuel sending gasket.

No fumes, full tank of gas, no gas drips on the garage floor with a full tank. New hoses and clamps. Fresh rubber undercoationg all around.

John_AZ
1988 924S + 1987 924S

[Rasta Monsta]

Well, I think I decided to toss mine and update to plastic. I'll post a How-To at the 924 Board.

[Schumi]

Originally Posted by John_AZ

The frame is not very rigid. If you jack the car from one back wheel and try to open the rear hatch, The hatch pins bind on my car.

The reasoning behind this is that the suspension for the rear, being trailing arms, mounts way forward on the car under the back seats. This area is highly stressed and rigid. Everything after that can be wet noodles. It's not the best, but it makes for a light car.