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Gas fumes? Tank leaks? Read this.

Hi folks,

I'm creating this post to shed some light on a common problem that I have found with the steel 924 / 944 fuel tanks. Hopefully, it will help some others.

I have an '87 924S that I purchase a number of years ago. From the time I got it home I noticed a strong fuel odor in the cabin. I took the standard approach by replacing all of the vent and fill lines that I could access. I checked the vent lines to, and the function of, the charcoal canister. Then I carefully sealed the interior filler neck cover. This did not solve the problem.

I put up with the problem for a few more years, until my wife refused to ride in the car with me due to the fumes! At this point, I decided to drop the transaxle and remove the tank for closer inspection.

The top of the tank has a number of formed features for strength and clearance of vent lines. There is a central formed feature that looks like a dimple, formed deeper than the others. There are two sharp radii bends on the edge of this deeply drawn feature which are the source of the problem.

During manufacture, the steel is stressed excessively at this location. After a number of years of expansion and relaxation of the tank due to vapor pressure, small cracks develop. Fuel and vapor then leak from these cracks. Just a note - I'm a mechanical engineer, and I design stamped / formed steel components.

See attached photos.

From what I have found, this is a common problem. I have purchased and returned three used tanks with the identical problem. Yesterday, I pulled another tank (#4) from an early 944 with the same cracks and fuel stains. I have sent a complete report with photos to Porsche. Porsche showed no interest.

I have had no success with the traditional repair methods due to the location of the failures and flexing of the tank. My remaining options are to solder with shaped copper patches, or to convert to a later model plastic tank. One good thing is, from lots of experience, I can drop the exhaust, transaxle and tank in under an hour!

Thanks, Neil


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Old 11-14-2005, 12:21 PM
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That's pretty neat! Too bad you didn't get a reply from Porsche AG, but they don't seem to be the best for customer service.
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Old 11-14-2005, 01:11 PM
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that would probably be why mine poured gas all over the muffler when i filled it up the other day.....thanx for the info...
Old 11-14-2005, 02:32 PM
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this might explain why, if i fill my tank all the way, i'd smell gas in my '83.
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Old 11-14-2005, 02:37 PM
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Neil, you made mention of plastic tank from later years. What year and model? Direct replacement? Any info would help. My wife refuse to ride in my 87 951. Thanks.
James
Old 11-15-2005, 11:52 AM
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Why can't you put a gob of gasket sealer over it?
Old 11-15-2005, 12:24 PM
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long ago I had a '69 mustang with a gas leak from the tank bottom (easy access at least!)...I cleaned the area and glob'd a tube of silicon sealer onto a pie plate and squished it against the tank. worked fine for years !
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Old 11-15-2005, 12:37 PM
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That's what I'm going to try....can't lose anything but the time to try it....
Old 11-15-2005, 12:40 PM
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Hey guys:

These are the repair techniques I attempted on the original tank:

1. Drilled a small hole at the end of each crack to halt further propagation. Opened the crack with a fine Dremel bit so sealant could mushroom into opening (instead of just sitting on surface). Thoroughly sanded surface and cleaned with acetone.

2. Applied JB Weld.
Result after assembly: JB Weld cracked - tank leaked.

3. Purchased two-part Permatex Fuel Tank Sealant (comes in a stick). Cleaned and prepared tank as before. Applied per instructions. Applied some air to tank to simulate flex from vapor pressure.
Result: Sealant bond with surface cracked before installation.

4. Purchased Permatex epoxy resin / fiberglass tank patch kit. Installed nicely, passed pressure test, allows some flexing. I thought this was it!
Result after assembly: Fumes in car. Applying air pressure to filler neck results in hiss from top of tank. I am assuming this patch failed too.

During this time I was trying to source a good tank, and found all to have the same cracks.

This is why I am investigating a solder repair or switch to the plastic tank.
Jimmyvirus: I am researching the swap right now, but it looks like I can use the 85.5 an newer 944 tank in place of the steel unit. I will need to acquire all the associated vent lines, filler neck, and mounting straps to make it happen. If anyone knows otherwise - let me know

Cheers, Neil
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Old 11-15-2005, 07:07 PM
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Did you ever try silastic,or something that is more flexible?
Old 11-15-2005, 08:46 PM
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Thanks Neil. I'll keep an eye out for your post of successful swap.
James
Old 11-15-2005, 09:36 PM
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I have exactly the same situation in my 87-924S. Havn't spent any time on the tank yet. Just everything alse. Will be looking at the tank the winter. Anyone know if my tank is metle or plastic???
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Old 11-16-2005, 06:34 AM
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that sucks.
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Old 11-16-2005, 12:20 PM
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Konan:
As I found, JB Weld & Permatex-in-a-stick were not flexible enough. I tested the fiberglas-reinforced Permatex material on some sheetmetal first. Results were good when bending the test piece. I plan on dropping the trans and tank on Saturday morninig to check the latest failure mode. I'll make sure I report my findings.

Thanks James.

hpaulb:
Your tank is steel like mine. 1983 to 1985.5 944's had steel, later 944's had plastic. However, our 924S models ('86 thru '88) had steel.

Neil
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Old 11-16-2005, 06:48 PM
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I would try copper sheet soldered to the tank--- if there is room enough.
Jeff
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Old 11-17-2005, 07:10 PM
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Hi Neil,

Great post, I will link to this thread from my wasserpumper site. This is an informative thread, great photos, good handle on the issues, and big safety implications too. Well done.

P
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Old 11-17-2005, 08:03 PM
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Re: Gas fumes? Tank leaks? Read this.

Quote:
Originally posted by Neil - Colorado
Just a note - I'm a mechanical engineer, and I design stamped / formed steel components.
Neil, I'd like to talk to you about some metal stamping projects that I've been stumbling over for a couple years.

CHeck your PM's please.
Old 11-18-2005, 01:17 PM
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So are the 85.5+ tanks are all plastic?

On a side note, I have the tank from an 83 sitting out back by the garage, I will inspect it for those cracks. You mentioned that they were present on all of the tanks you checked.
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Old 11-19-2005, 05:27 PM
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Thanks P!
It seems that a lot of people have problems with fumes or leaking. I hope this helps some of them.

Zero10:
All the info that I have shows that 85.5 and newer are plastic. Take a look at ***********'s parts diagrams for the 944. They show the two tanks and their respective model years.

Mr. Wilk:
I have had no luck finding someone who would weld the tank in the Denver area. If someone can suggest a place, that would be great!

I removed the tank again this morning. A small part of the fiberglass Permatex separated from the steel.

I have come across a possible problem with the steel to plastic tank swap. In my early-style car, there is a crossmember that is integral to the chassis, from which the transaxle is suspended by two mounts (see photo). From the very few diagrams that I have seen, it appears that the later cars use a removable crossmember, from which the transaxle is suspended by a single, central mount. Can someone tell me if this is the case?

The leading edge of the tanks protrude between the crossmember and the trunk floor in both early and late cars. Due to the possible differences in the space available between the crossmember and trunk floor, I'm not sure if the two tanks are interchangeable. It appears that the later plastic tank is thicker at the leading edge than is the steel tank. Any info on this would be graetly appriciated!

Thanks! Neil
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Old 11-19-2005, 06:27 PM
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Excellent post and information. I second the idea of getting it welded while it's out of the car. Or replacing the tank with a new one - spare parts for these cars are anything but rare these days. I'd probably look at methods of strengthening a "new" (used) tank though to proactively prevent failure in this location. Perhaps better tank vents? Reinforcement?

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Old 11-19-2005, 06:59 PM
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