Galvanized Fuel Tank

[412s2]

Is there any reason why fuel tanks on cars aren’t galvanized? I once had an 8 year old Audi 100 quattro that had spent most of its life on the Shetland Isles getting blasted by sea water, the galvanized body shell actually stood up to this punishment extremely well, but anything that wasn’t galvanized had suffered badly; it was a pig to work on, everything was solid with corrosion. I always wondered why Audi didn’t galvanize the metal fuel tank strapped to the bottom of the car, it only seemed to be coated in a thin covering of black paint and yet was exposed to the worst of the filth thrown up from the road, eventually it started leaking out of several rusty pin holes. Very annoying!!

Anyway, I have the fuel tank out of the 412 Variant as I was welding a little bit of the bulkhead, the tank looks to be in very good condition, should I get it hot dip galvanized?

Galvanized Audis and 50 year old Massey-Ferguson tractors are the only metal things that seem to survive long term in the Highlands of Scotland!

[412s2]

I have been having an interesting e-mail discussion with Albert in Quebec on this. Albert told me that the reason fuel tanks are not galvanized is because the fuel reacts with the zinc and gets burned in the combustion process creating a toxic pollution problem!! He also told me that corrosion of metal fuel tanks in the past wasn’t such a problem because of the greater amount of lead in petrol at that time, some of it would bond to the sides of the tank and create a sacrificial barrier protecting the steel. This could explain why the tank in my Type 4A Audi 100 rotted so fast, it had only ever ran on unleaded fuel.

http://en.wikipedia.org/wiki/Galvanic_series

Albert also told me that petrol is a good electrolyte, which is why we don’t have copper fuel pipes fitted to our cars; it would cause the steel fuel tanks to sacrificially corrode and protect the copper pipes! I told him that is was not uncommon in the UK to find cars retrofitted with copper fuel pipes. I did a quick search on the internet and found one MOT (the annual UK vehicle safety/roadworthiness inspection) tester that said he would pass a car fitted with copper fuel pipes. http://forum.triumphdolomite.co.uk/view ... =5&t=12420

This then got me thinking about copper brake pipes, I can remember reading on this forum a while back about Kieron’s BMW brake modifications and someone was surprised at his use of copper tubing for the brake pipes. It seems that North Americans don’t use this, while it is the standard replacement tubing for brake pipes in the UK (along with Copper Nickel Alloy). I have never seen a car fitted from the factory with copper brake pipes though, only coated steel. Is there a reason for this? How good an electrolyte is brake fluid? Could it cause a problem in brake calipers and cylinders or is the flow rate not great enough?

[albert]

412s,,i geeve you ,, one suggestion for to see the différence wy the majority of the brake line are made with the steell pipe,, if you cut one section on the steel pipe ,,if you put this small section 4-5'' long in the front of a big light or the big sun light,,, inside of the steel pipe you can see a strait line,,longitudinalll,,,, and now doo the samething with the cupper pipe ,, the construction is différent ,,if you look inside of the cupper pipe you can see a kind of twits like a screw,,if you use this cupper pipe for the brake ,,with the hight pressure on the oil brake ,,the cupper pipe take a kind of expention like a spring ,, and you d,t have that with the steel pipe, if you push a very very hight pressure on the steel ppipe they open on the longitudinal of the pipe like 3'' long on 5'' total,,there is the major reason they d,t use the cupper pipe for the brake,, for the chimic réaction with the oil brake and the cupper,,i know the oil brake can dilute the cupper,, and many more thing,,albert

[albert]

one more thing,,412s,, d,t doo an error with cupper pipe,, sometime you can see a pipe with cupper or galvanise plating,outside ,if you look inside it is a steel,,

[raygreenwood]

Solid copper is far too weak for brake lines. Copper is used in very humid and salty areas to protect against corrosion (England). But copper plate only. Actually fuel is not really a good electrolyte at all. It has no electrolytic properties. That is not really the function that keeps rust away.
A full fuel tank keeps oxygen away from metal. In areas that are simultaneously cold and humid...and have varible temps...waier condenses out of air like mad inside of fuel tanks. Thats what causes the rot. Its heavier than fuel and stays in the botom. The recirculating nature of the fuel ring insures that it just keeps collecting unless you use an alcohol or acetone based additive to absorb and burn the water. Thi s one of the two reasons why most cars have plastic fuel tanks now.

In the fall months with alternating freezing and non freezing days with humidity....keep your tank full and once a month add an alcohol additive. Galvanizing is unnecessary. Ray

[412s2]

Hi Ray, it’s funny how you think of England as a humid and salty place, it’s were I go if I want a decent old car because it is so much drier there! I suppose everything is relative! Where I live on the north west coast of Scotland it is quite unusual to find cars over 10 years old and most of them are either German or Swedish, anything else dissolves!

We do actually use solid copper pipes as the standard replacement brake pipe in the UK.

http://www.demon-tweeks.co.uk/products/ ... =S/CHCP316

It is made to BS2871 and that means not less than 99.85% copper. Brake lines are inspected every year on cars over 3 years old in the UK, I would say that most cars that require a replacement brake line are fitted with BS2871 copper pipes. From my experience you can use it only once though because after it has been on the car for a couple of years, it is impossible to remove the unions from it without damaging the pipe. The alternative, which is slightly harder to find at your local auto store is copper nickel alloy pipe (90% Copper, 10% Nickel), it is more expensive (therefore not as popular when fixing up a daily driver) and it’s what I use on my car. It is slightly more golden in colour that the pure copper pipe; looking at the colour of the pipes on Kieron’s car, I would guess his are pure copper.

http://www.shoptalkforums.com/viewtopic ... 2&t=127231

Further reading: http://www.copper.org/applications/auto ... _tube.html

I’ve read a bit about copper acting as a catalyst in the oxidation of petrol on some US based car forums, but this might be hearsay as I haven’t found a reliable source to confirm this. Using copper pipe as fuel pipe seems to be quite popular in the UK, especially with people restoring older classic cars. Thankfully the steel ones on my 412 still look great

[albert]

NEIL,,here we have the most hard winther in the word,, we have many salt on the road,, plus we have a weather with 30 deg, différence in one night,,and very humid , and here we have many car more of 10 years,, what we do,, we shoot every year a spécific oil for the rust prooff,,onder the car and inside of the doors,, albert

[412s2]

Hi Albert, I am always interested to hear good ways of slowing down the corrosion process!

I would wager that the extreme cold temperatures that you get in Canada actually slows down the way the salt reacts with the metal of the car. Where I live it rarely gets down to 0C in the winter (we have palm trees growing in my village, at 58 degrees north!) but they still have to salt the roads. In the north west Highlands we have an average rainfall of around 3000mm (3 metres/120 inches!), so for much of the year anything lying outside is damp and never really gets a chance to completely dry out.

http://en.wikipedia.org/wiki/Scotland#Climate

http://fr.wikipedia.org/wiki/Géographie ... sse#Climat Pour Albert

[albert]

NEIL,,here we have a spécialist shop for rust protection,,if you d,t have this spécialist in your contry,, wash your car ,,in the fenders and onder the car with hot wather and spray the oil with the zink in the oil ,,you can find that in the car shop,,albert

[raygreenwood]

I learn something every day! Solid copper! I figured it would have problems with flare unions. Is the wall section thicker than steel?

Yes...in places with lots of road salt, you are actully well off when it remains freeezing for most of the time . Its the combination of road salt, and alternate warm wet periods that do the most damage....kind of like where I live now. Ray

[wildthings]

There are certain places where a galvanized or zinc plated tank might help. Any tank that can catch water and debris on top of it is a candidate for getting rust holes in the top. Also a lot of tanks can sit on wet areas or rust out along support straps. Several ACVW tanks are in one or the other of these categories.

Interesting on using copper for brake and fuel lines in the UK. I would have thought it lacked the strength and rigidity to do the job. When I have seen it used for fuel lines it has always been well kinked and down right nasty looking. As far as I know US spec brake line is zinc plated inside and out, and when I have used it for fuel lines it has worked fine.

[Lars S]

Over here, where we have salt on the roads six monts of the year , all aftermarket brake lines seems to be of Copper/Nickel (Cu/Ni) type. They look like copper, are easy to bend and do not corrode despite the environment.


/Lars S

[412s2]

I’ve seen the copper and copper/nickel pipe sold with 0.71 and 0.9mm wall section thickness.

What kind of zinc impregnated oil do they spay the underneath of your car with in Canada Albert? It sounds interesting, do you find it to be very effective? I’ve never heard of such a thing before.

I am always a bit paranoid about locking moisture between any underbody coatings and the body of the car. When I got my 944, I jacked it up and jet washed the underneath of it, left it a couple of days to dry then backed it up into the garage. It sat in there while I did the work on it over the winter (hopefully drying out completely in the process!), before I put it back on the road in the spring I coated the underneath of it with a combination of Dinitrol 3125 (a soft waxy film that is meant to be good at creeping into nooks and crannies) and 4941 (A more durable hard wax). It appears to be holding up well. I have several tins of these products to coat the 412 Variant with before I put it back on the road.

As far as my fuel tank goes, I gave it a closer look yesterday, there is a bit of surface corrosion on the inside of the tank so I am thinking of using this method to fix it up: http://www.frost.co.uk/how_do_i_explained.asp?hdID=32 I have a friend that restored an old motorcycle tank using POR15 and was very pleased with the results.

[raygreenwood]

Before you get too hung up on some of those products you might want to read some of my posts under the "rust" sticky on the bodywork forum.

Those are good products but can be greatly limited in effect if you have lots of scabby rust in the tank. Those products do not work well if rust is over about .002" thick (common). One of the best ways to absoluetly get rid of all of the rust in the tank is to use either a 50/50 water and muriatic acid mix (common swimming pool acid)...or you can use it stronger if you would like. Acid literally disolves all rust of any thickness right down to bare metal....all of it. No slight patches of anything left.

One of the active ingredients in the metal prep section of POR-15 is phosphorci acid. Phosphoric acid is hands down the very best rust and surface prep treatment and primer. It converts rust to iron phosphate. All converted areas will NOT rust again. However...it is a low solution strength acid. It cannot get through more than maybe .001" thick rust depending on its porosity. Any rust left underneath any coating will continue to rust though more slowly.
The Iron phosphate is a superb primer for any paint and coating. Better even than zinc diphosphate. The metal prep in POR-15 and other similar products depends on the layer of iron phosphate coating being there so it can bond to it. But....iron phospahte plates poorly to clean unrusted metal.

The best way to use these products is to totally derust your tank so there is no rust whatsoever. Then wet the steel with water and let it sit for a day. This promotes a very thin quick flash rusting on all surfaces. If the rust is not fully coating the inside....wet it again and let it sit. This does not take long. After acid washing the surface is so well degreased that flash rusting starts in minutes.

Then use a phosphoric acid product like Ospho (available at most hardware stores). Slosh it around and get everything coated. Let it sit for 24 hours. If you can still see any non- bluish black areas...slosh around some more and let it dry for a day. Then drain...and solvent wash...then use a fuel tanking coating epoxy. Ray

[412s2]

Hi Ray, thanks for all the advice Muriatic acid is not that easy to come across here in the UK. I’ve read your “rust” sticky in the Bodywork Forum in the past, it really does sound like the way to deal with rust. When I was at my local hardware store (a 5 hour round trip unfortunately) I asked them if they had any muriatic acid for swimming pools and they just stared at me blankly; private swimming pools aren’t exactly common in Scotland. I’ve since found out that another name for muriatic acid is hydrochloric acid, this is classed as a poison in the UK and is therefore very hard to get a hold of unless you can prove you work in forestry, agriculture, horticulture and the like...

I did a quick search for a UK based swimming pool chemical specialist in the UK, to see what they offer for reducing the pH of swimming pools, they sell Sodium Bisulphate (AKA sodium hydrogen sulfate, NaHSO4)! http://www.swimmingpoolchemicals.co.uk/ ... 1604dql001 I read in Wikipedia that it is used in metal finishing, do you have any experience with it?

I haven't been able to find Ospho in the UK either, but I'm guessing it is very similar to the POR-15 metal prep stuff, phosphoric acid?

Thanks again It's all very interesting!