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1973 911-T (CIS) Fuel Tank Exposed

After having my fuel tank purged by the local rad shop, I decided to replace it with either a new plastic tank or a fuel cell. In order to have a better idea as to the havoc thirty years of service inflicted on it's innards, I had the old tank sliced open along it's seam. The attached photo shows both halves with the lid removed from the plastic fuel pick-up canister.
There was still (after cleaning) rust particles and debris remaining in the bottom of the canister.

More detailed photos will be posted soon.

These may be of interest to those 911 owners experiencing fuel delivery problems.

Paulo



Old 09-07-2003, 03:24 PM
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Did the tank *leak*?
If not, it looks like you cut up a tank in fairly decent condition. Your pictures show a bit of surface rust that could have been easily dealt with, using a product like POR15 tank sealer.
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Old 09-07-2003, 03:32 PM
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That tank looks to be in fine condition.....what do you think they have fuel filters for? Sorry I think you trashed a perfectly good fuel tank..

IMHO as some like to say
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Old 09-07-2003, 03:57 PM
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I have a question about the design of this tank if anyone can answer. The bubble under the spare tire? How does gas get in there? I'm no super genius or anything (as I claim in my name) but if the car is sitting still while your filling it up and that bubble is full of air wouldn't the air just stay in there? And if it does, why would they design it so it could never be completely full?
And Doug, I was told you can't use the por15 in our tanks because of the plastic. It won't adhear to the plastic so you'll end up with some hardend por15 floating around the tank. Its hearsay, but I didn't use it because of that. I used the POR15 Marine Clean cleaner though. It seemed to work well.
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Old 09-07-2003, 05:11 PM
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Here are two additional photos of my tanks internals. The first picture is a close-up of the pick-up canister showing the central ring opening(where the screen protrudes into the canister). A slot around the circumference of the ring is the source from which fuel is sucked into the large diameter fuel delivery line. The smaller diameter line on the right is the fuel return and it returns fuel into the semi-circular channel where it flows back into the "ring" area of the canister. The second picture shows the very small orifice in the bottom of the dividing baffle from which fuel flows into the canister side of the tank.

Doug: The tank did not leak, however, I did not want to use a 30 year old fuel tank (with some rust and debris) to feed fuel to a new motor with electronic fuel injection. Also, I think tank sealers are a questionable patch that may cause additional problems like blocking that very small opening in the baffle.

Tim: The tank wasn't in fine condition and I didn't want to jeopardize the operation of a new motor (and considerable expense) by using it. My main purpose in trashing this tank was to post photos of it on this board so other members could see what is inside and make more informed decisions as to what to do with theirs. I would not have sold the tank to anyone (it has minimal value) so it was sacrificed for the greater good.

Mike: Good question about the design of the tank. I have no theories! Considerable fuel capacity was sacrificed for the spare.

Paulo


Old 09-07-2003, 07:10 PM
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Oops..., here is the second photo of my exposed fuel tank.

Finally getting up to speed on posts.

Paulo

Old 09-07-2003, 07:14 PM
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Thanks for the pictures! I have wondered what the inside of my gas tank looks like.

-Rob
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Old 09-08-2003, 09:54 AM
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Nice work Paulo! Good or bad tank..it's always good to have folks willing to make the sacrifice so that we all learn! The close ups make the tank look pretty bad.

As for that air in the spare bulge...who cares! with ~22 gallons capacity...do you really need more? It surely does trap air, which is why the capacity fluctuates a bit...faults mileage calc too..
Old 09-08-2003, 10:03 AM
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Thanks Rob and Souk for your comments.
My fuel tank is (was!) a stock 62-liter (16.4 US gallon) item. The 22 gallon capacity that you mention Souk, is the later model 85-liter version.
Will attempt to post remaining photos tonight.

Paulo
Old 09-08-2003, 12:51 PM
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Thanks Paulo, we murder to dissect! Although this may have been more of an autopsy. All in the name of science! Is the inside of that tank galvanized?

Souk, thanks for the info, I'm just curious. I think the parts of the inside of the tank that are exposed to air more often are more likely to rust. So having the empty bubble would be a possible liability. When I had mine out last week someone had mentioned that the top of his tank had lots of rust where the bottom looked pretty clean. Its just a theory... That wasn't the case with mine, the top of mine looked clean. But it ain't easy to see everything through those holes in the top and bottom.
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Old 09-08-2003, 04:24 PM
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Here are two additional photos of my dissected fuel tank. I cannot say for certain, but I don't believe the inside surface of the tank is galvanized.
I have not researched what options are available to early 911 owners regarding replacement fuel tanks. Performance Products advertises a 1965-1973 911/912 Reproduction Tank (made of galvanized steel) for $299.95(US); although it is not applicable to 911-T CIS models. Stoddard's 1997 catalog priced OEM tanks for 1973 models at $ 1,469.14(US). The later 1974-1989 tanks were piced at $ 982.16(US). FVD-USA in their 2001 catalog had early (repro. or OEM?) 62-liter steel tanks at $625.00(US) and the later 85-liter steel tanks at $770.00(US).
I have heard that the factory is considering having a supply of 928 plastic tanks made. I haven't checked with my dealer to see if any OEM 911 tanks are in inventory and their related pricing.
Maintaining 911s is not an inexpensive undertaking. There are some areas where money is well spent and having clean fuel delivered to the engine is one to say nothing of the safety issues.
I will probably buy a fuel cell because my car will be entered in tarmac rallies. If not for this I would try to find a plastic 110-liter RSR tank which would end rust concerns for the life of the car.


Old 09-09-2003, 09:20 AM
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Where are the pictures?
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Old 07-26-2006, 09:26 AM
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I took out my 1973.5T fuel tank this past spring, emptied it, and brought it in to a radiator repair shop where it was "boiled " in a mild caustic solution. They had to drill a few drain holes beyond the other drain area for good flow thru circlulation and drainage. They welded up the holes afterward. Then they coated the inside with "redkote" which is an industrial and military coating that seals tanks. Bullet proof they say.

I then replaced the ilarge nternal fuel filter that screws in through the bottom , removed the remainder of that tenacious exterior coating, sanded it down, applied a cover of POR15 (silver) and recoated with Wurth after that. Looks brand new on the outside. So far I have had no issues on fuel line or filter blockages or acceleration problems. I think the $200 investment was well worth the effort. The last time I called my local Porsche dealer a factory OEM replacement was $850 and that included my PCA 15% discount!!

Unfortunately, I do not know of any reproductions of the 73.5T tank, or ones in great shape, which would be as rare as a t-Rex skull!!

Appreciate the photos......very educational on the inside stuff.

Looks to me like you can salvage the thing by re-welding.

Bob
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Old 07-26-2006, 09:47 AM
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Paolo...
After looking again at your photos, the repair to remove or seal the rust is very easy. Check out POR 15, which will permenantly seal everything as many will attest. I would have that rust sand blasted out and then coated. A good shop could weld that back together for a very good refit. I think you shopuld try that first before laying out the cash for another tank. Your is very nice actually, for 30+ years of use. You'll save hundreds here....

Use a coating of POR15 on the outside as wel or prime with rust preventative and coat with Wurth, which gives you that pebble, rubber like coating appearance. They sell by the can (four - six cans needed).
Replacement filter with new gasket is $30 at the dealer. Add new hoses while the tank is out and your on your way.

Good luck

Bob
Old 07-26-2006, 09:55 AM
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Hmm, these tanks have an external filter that screws into the canister?

I guess that is how they differ from the earlier tanks with the finger screens?
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Old 07-26-2006, 10:04 AM
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Paulo - BIG kudos on the extra effort made on behalf of us on the board. I don't think anyone means to criticize you or your concerns for your new engine. Believe me, if I'd just dropped thousands on one I'd be very concerned too.

But maybe as Bob points out there is a real silver lining to this. Your shop cut this thing so professionally that you can media blast it clean as a whistle, coat it (making sure no ports are blocked), re-weld it and then you will KNOW ABSOLUTELY your tank is original, perfectly clean in & out as well as coated so rust issues will never be a problem again. All that and a hell of a lot cheaper than a new tank. You have an opportunity to have something none of us have!

Any way you decide to go, thanks for posting the pictures and good luck. Hey, let us know what you end up doing. Dan
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Old 07-26-2006, 10:18 AM
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Quote:
Originally posted by Mike Kast
I have a question about the design of this tank if anyone can answer. The bubble under the spare tire? How does gas get in there? I'm no super genius or anything (as I claim in my name) but if the car is sitting still while your filling it up and that bubble is full of air wouldn't the air just stay in there? And if it does, why would they design it so it could never be completely full?
When the gas is stored underground and is pumped into the tank at 100 deg F it expands quit a bit. I think that air filled dome is there to accommodate expansion.
Old 07-26-2006, 10:20 AM
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Great pics!

John, Grady has posted a diagram like pic of the fuel filter in (some as I recall) of these tanks on another thread.

Where did the filter go in the pics above? I thought it went in horizontally somewhere (?) Or did it screw in vertically in the center of the spiral piece?

And where did you get a plastic tank?
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Old 07-26-2006, 10:44 AM
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So thats what is in there...
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Old 07-26-2006, 11:08 AM
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I agree with paulo, though I think saving the tank is a good idea. My '73 had constant running problems associated with the carb jets (Webers). I would clean them and they would clog again in short time...a real nuisance for track work. I spent money on the finest filters, only to have the problem re-occur. Finally got PO'd and replaced the tank with a Fuel Safe, which was safety related, as well as problem solving. Voila, no more problems! I had my mechanic toss the tank as I didn't want to deal with it and he didn't want it either. Best $650 I spent (this cell was removed from a heavily damaged track car, rear only).
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Old 07-26-2006, 11:35 AM
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