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
