Heavy corrosion, gas tank, what's the cause?

[gary505]

I removed a gas tank from a 1999 Chevy s-10, 4.3, with 93K miles.
Tank, filler neck and entire tank had very heavy corrosion, fuel pump pressure was low and fluctuating, filter had ruptured from rust.
Fuel was Shell and Town and Country, local farm store brand, no additives or E-85 were used, as per owner, if you can believe them?
It had heavy, even corrosion thru the entire tank,even filler neck and vent tube. The trouble just developed over 2-3 weeks, no driveability problems before this. The pump with it's 75 micron OEM screen would not have lasted very long under these conditions.Attached picture of filler neck and vent tube. Full even rust on ALL surfaces.
Was this a plating problem from the factory or was something in the fuel that ate the tank up, ideas????
I flushed lines, replaced tank and pump assembly and filter, used new fuel, so far no problems.

 

[Tmoose]

I think the rusting was going on long before the driveablity problems finally surfaced.

I'd look at another tank from a vehicle of similar age in the area. If it looks a lot better I'd suspect some fuel chemistry experiments had occured a few times in the last 15 years.

 

[MikeHalloran]

Speaking of owner behavior, habitually filling a tank partway, a few dollars at a time, is usually alleged to allow more corrosion than always filling the tank.






Mike Halloran
Pembroke Pines, FL, USA

 

[RossABQ]

I just looked down my 98 S-10's filler with a borescope; nothing but clean shiny metal as far down as I could see. It has been run on E-10 most of its life. Is this particular S-10 a Flex-Fuel model? Lots of problems with those, but corrosion like that isn't one of them AFAIK. I believe their tanks are different materials than the base models.

 

[BrianPetersen]

Most likely, a fuel tank sealing issue has allowed moisture-laden air in and out of the tank. If the vehicle is exposed to large temperature fluctuations and a humid climate, that's not going to help. Geographically speaking, where are you?

 

[gary505]

The 1999 s-10 is a standard model ,no flex fuel and it did not have any evap codes stored or current. It is in central Kentucky. Truck was originally from Florida, but owner has had it for 5 years up here with no problems. I would say salt water might have been the cause of the problem, but it is not likely that the pump would have lasted any time under the severe conditions, without causing any drivability problems or codes.
I have replaced over 300 fuel pumps thru the years and have never seen corrosion to this extent in any vehicle.
Any metallurgists out there?????
I have more pictures and fuel filter contamination pictures, if interested.

 

[RossABQ]

Could it be a hurricane victim?

 

[drwebb]

Serious vapor phase corrosion there- I suspect that's key. Lots of tanks rust (fixing a pin hole leak on my old MC this weekend), but not usually ABOVE the fuel line. I have seen chlorinated solvents in enclosed humid spaces attack steel (presumably from hydrolysis-generated HCl), but any that got into the fuel I believe should have wiped out the 02 sensor. Just a brainstorm . . .

 

[tbuelna]

Looking at that photo, there is some serious corrosion. It does not look like corrosion that would result just from humidity/moisture/condensation of the air trapped in the fuel tank. That extreme type of corrosion would only come from some aggressive chemical contaminant present in the fuel.

 

[gary505]

drwebb and tbuelna Both of your suggestions seem possible.From my practical experience this has to be something more than the usual moisture/rust problem.
It looks like vapor was responsible for causing some of this since the tank was covered with rust very even throughout.
Years ago we tracked down, no start cold, on Ford fuel injectors. Turns out the customer was buying fuel at only one station and we sent the injectors to be analyzed. They found that they were not using enough anti-corrosive additive and they were not mixing it correctly in the tank trucks, they we just pouring in 5 gallons after truck was filled and they needed to have it injected into filler stream for through mixing.
Wish I could track down the cause of this problem too.
Gary Wonder if GM would comment on this problem if I sent pictures???

 

[allencr]

Magnetic?
Mine looked exactly the same and rust was the first thought, but the metal was really corrosion free, untouched, just a little stained.
The 1/4 tank of 2+year old gasohol had left a really nasty smelly smegma everywhere inside. The fuel line & injectors were OK, so I think it was the fuel plus fresh air combo that did it, helped from opening the tank to siphon a few times.

 

[tbuelna]

The picture provided looks like where the sending unit/fuel pump is mounted. While there is substantial corrosion on the inside surfaces of the tank, there is no significant corrosion on the outside surfaces of the tank. Water would not produce this kind of corrosion unless the entire tank was filled with water for an extended period of time. Is it possible that the vehicle was submerged in water at some time? Or was the vehicle (or its fuel tank) stored for an extended period where water could fill the tank?