Oil tank corrosion?

evan9eleven · evan9eleven's Garage

So, I replaced my oil level sender a few months back as winter was setting in, and am just now getting around to repairing the wiring to it, along with installing a new rubber boot over the connection. Before I replaced the sender last fall I used some degreaser on the oil tank to clean it up so no dirt would end up in the tank.

When I looked at the tank tonight I noticed rust on the nuts for the sender, no big deal, but there appear to be a few rust spots on the tank too-- along with some glistening droplets of something. OIL! Wet droplets. As though oil is weeping through the tank walls. This can't be, right? Mine is a nearly rust-free car, so its not seen winters and salt so I'm puzzled. The car hasn't been run in two months. Pics for reference:

chris_seven · 02-02-2015, 09:14 AM

If it looks like a duck, walks like a duck and quacks then it is quite likely to be a duck

If it is oil then the only place it can from will be inside the tank, just be bold and remove the sealant and check it out.

JohnJL · 02-02-2015, 10:07 AM

The tanks are coated with copper in an attempt to delay corrosion, but it still happens. Water accumulates in the tank from the hot-cold cycle condensation (ever see the yucky yellow mayo/foam inside your oil cap?) Some degreasers are also caustic so can cause or make a problem worse. Ever leave some bolts in a degreaser vat for a few months? They corrode...

Mark Salvetti · 02-02-2015, 10:36 AM

What's odd is those leaks (if that's what they are) seem to be pretty high up on the tank wall. What does the bottom of the tank look like? If it was condensation inside the tank that caused this, wouldn't you expect the worst damage at the lowest point?

Mark

pors1968 · pors1968's Garage

It might be some degreaser Under coating but it look it been corroded with dirt road.Top must be worst.

Gav · 02-02-2015, 04:03 PM

Is it definitely oil?
Perhaps the degreaser has reacted with the body deadner?

safe · safe's Garage

They seldom rust from the outside. If they leak there is a lot of rust on the inside.

Start looking for a replacement tank.

evan9eleven · evan9eleven's Garage

I was afraid of that. I'll inspect more closely when I have the car in the air this weekend and report back, but the substance sure seems to be oil. What would allow the inside of an oil tank to rust first is an obvious question... humid climate and not being run for months on end in winter is my best guess.

Porboynz · Porboynz's Garage

I will place my money on it being the under seal bleeding or some thing other than internal rust. Reasoning that rust would be at the top of the tank.

porschetub · porschetub's Garage

Quote:

Originally Posted by safe

They seldom rust from the outside. If they leak there is a lot of rust on the inside.

Start looking for a replacement tank.

I have one like that and only recovered the console,it had been brazed,soldered and then covered in sealer ,the inside cleaned up nice till i found the outside was like a battle ground.
Hated the dishonest seller for a while,till I found the console as in perfect condition and now worth good money

safe · safe's Garage

Quote:

Originally Posted by Porboynz

I will place my money on it being the under seal bleeding or some thing other than internal rust. Reasoning that rust would be at the top of the tank.

Well, I assume that evan9eleven is correct in that it is oil, but the area might need a cleanup to confirm.
It is a little strange cause I thought that an 81 would have a stainless oil tank. On the other hand they can corrode too.

evan9eleven · evan9eleven's Garage

Quote:

Originally Posted by safe

Well, I assume that evan9eleven is correct in that it is oil, but the area might need a cleanup to confirm.
It is a little strange cause I thought that an 81 would have a stainless oil tank. On the other hand they can corrode too.

After doing some reading I see that the later tanks are often mentioned as being stainless. Yes, stainless can corrode if subjected to road salt and other nasty stuff... but it takes some doing so I'm even more surprised if my tank has rusted through. I also read that the vapors in our oil tanks contain a lot of byproducts of combustion that are corrosive too, but again I would expect to see this effect more at the top of the tank. I'll definitely have a closer look ths weekend.