Expansion tank interior paint

I would say no to coating the inside. The reason is that if and when there is a small defect in the coating, all the corrosion activity gets concentrated at that small point and it is like a drill going right throught the wall. Right now you have general corrosion spread over a larger surface area and it will take a lot longer to go through the tank. In addition, the new glycol/water mix will have corrosion inhibitors and those will at least slow the corrosion process so you can enjoy the tank for years to come.

 

A friend of mine had rust problems in the Gas Tank on his Harley,He bought a type of sealer which work very good.Check at a Motorcycle Shop or Auto Parts Store.If it can hold up to Gas it might work for you.Also make sure it can handle the temp of the Antifreeze.Just a thought hope this helps.

 

Por15 has a gas tank sealer product for motorcycles. Not sure how it would hold up due to the heat in the expansion tank. Perhaps you can call their tech line and advise of your finding?

 

+1

 

I must be dumb.


I cannot picture this in my head and I know a little bit about physics.


I cannot see this "consentration" or "drill" effect. It is either going to rust at its own pace or it is not. I can see the interior paint flaking as the rust works its magic and those flakes clogging up stiff, though.



What am I missing?

 

You can use a chemical called ''Frametaux'', to neutralize rust.

Install a bonding wire between the tank and the chassis (a ground) to prevent corrosion inside your expansion tank.

 

Can you elaberate Constance?

I'd do this.

There are available grounds very nearby the tank.

 

Consider taking it to a radiator shop. They can "boil" it out to clean the interior and then coat it with a "slosh" coating of epoxy that is good enough to hold up inside a gas tank. It should be fine with a water/anti-freeze mix. The cleaning and coating will prevent any futher rust. I've never had it done with an expansion tank, but I did have it done with a gas tank, and it held up well for over a dozen years.

 

I would not coat the inside. Why not just replace it when holed or weakened?

Mine has rusted out at the top on the ribs; I understand that's where most blow a hole eventually.

Big difference vs gas tank. Hot & under pressure...

 

Radiator shop job: $60

New tank: $900

You do the math!

 

$900?! Where are you buying from, Tiffany's?

 

As noted, any decent radiator shop worth your time could coat this internally and it will work fine to limit future corrosion. My old one had been repaired/welded up three times by previous owners along the bead roll on the top of the tank. And it was leaking again on the final bead roll. Not to mention you can tell it had been welded up. So rather than doing another weld job, I replaced it with an aluminum one from Superformance....for around $350 plus shipping today. Comes with a new cap. Paint it black. And fits fine...as original.

http://www.superformance.co.uk/a-308/cooling.htm

I am sure there are probably other options....don't know who has them for $900!

Best Regards,
John M

 

If it's generalized surface oxidation (chemical corrosion), a coating will stop it. If it's galvanic corrosion from dissimilar metals or voltage leak (usually an infinitesimal current flow), the effect will be concentrated along the path the electrons are taking; e.g. near the attachment points or maybe the thermoswitch; and isolation from the current source is the answer. You didn't describe the extend or severity of the "rust" but yours sounds like old fashioned rust.

 

i just replaced mine (hole on the ribs) with a superperformance aluminum tank. didnt paint, dont mind the raw alu. just felt like the right way to go for reliability and longevity.

fair bit of surface corrosion on the panels under the tank - some Por-15 time ahead of me.

 

+1 on Superformance aluminum tank. I purchased a couple of years ago, had it powder coated black to match the original, and it has worked well.

 

The coating would provide a barrier from the corrosive environment of the glycol/water mix. When you have a large exposed metal area, you tend to get what is called general corrosion. The general corrosion occurs on the surface of the metal and doesn't penetrate the metal very far. When there is a protective barrier like an epoxy coating, no contact with the water occurs and thus, no corrosion. However, when there is a small failure in the coating, the protective barrier allows the corrosion to occur at only that point. It is called localized corrosion and forms a pit in the metal. Localized corrosion often has an accelerated rate of attack on the metal because of the increase in concentration of ions in the pit. Inside the pit the corrosion rate is actually higher and it is like a little drill making a hole in the metal.

Clearer now?

 

I shopped for 2 months for a tank for my 3.2... if you find anything cheaper, let me know!

 

I don't know about your 3.2, but Superformance carry most. I'm sure you could get one made from scratch for even less, given the original as a pattern (and certainly not saying it's for a Ferrari).

http://www.superformance.co.uk/308_a.htm