Fuel Tank Repair

[wbrian63]

Can a rusty W116 tank be sent out to be internally coated to encapsulate the rust?

There's the fuel return pot at the bottom, plus some sort of a baffle tank at the top that I'm concerned will give issues for the coating process.

What's the general concensus?

[CraigS]

I don't think I would waste my money. I had a pretty rusty tank and it would cut out going around corners because the line coming into the pot at the bottom was blocked with rust, and there is really no way to clean it. It is not fun when going around a roundabout and losing your brakes and steering !

[KenM]

The agent for POR15 here markets a kit they make for fuel tank cleaning and sealing, it contains cleaning solution, prep solution and sealer. Seems feasible, although it would certainly all depend on how well

you were able to get to all corners of the tank. The tank has to be out of the car for this to be successful.

[wbrian63]

I've read some posting about the POR15 kit, and with any kit of that sort, the key is getting the surface of the tank properly keyed to allow for as-designed bonding.

What I read over and over again was people that had problems with the coating bonding to the tank properly, and eventually (or quickly, depending on the author) delaminating and causing as much trouble as the rust that was supposed to be removed/encapsulated.

I remember a kit that you could buy that came with a length of chain. You put the chain in the tank along with some chemicals and rolled the tank around to allow the chain to dislodge the rust. No way I would do that with a W116 tank - would most likely destroy the return pot, and that's a disaster in the making when the tank volume drops low enough for the gas to rush away from the exit bung on a turn (which doesn't take long on a 6.9).

Because of the bottom-drain design of these tanks, we're really at the mercy of gravity.

There is no question in my mind that there is ZERO way to guarantee that the surface of the tank will be properly scoured of all loose rust when areas of the tank are blocked from any sort of mechanical interaction. The return pot at the bottom, and the baffle at the top will block any mechanical attempts to touch the surface of the tank where they are present.

No way I'm going to go through all the effort to fix the fuel system in #521 and put a rusty tank back in the car.

There's an eBay auction up right now for a "excellent condition" tank from an Arizona car for $175. That's a reasonable sum, but then there's the $95 the seller wants for shipping, and the possibility of damage during transit. A single drop is all it would take to ruin the tank.

What to do, what to do...

[KenM]

Or there's one on ebay.de for 900 euro, reconditioned not new.

What about a couple of inspection/access holes in your tank? If you suspect it's not worthy then there's not much to lose. If it turns out to be good, you would have proper access to do a thorough treat and

paint job and you would be able to patch and seal it properly afterwards.

[NormW116]

I had a problem with my tank recently. The car had not been used in years and there was lots of black tar gunk in the bottom of it as well as rust. It took me ages to decide what to do with it but in the end I decided against the POR15 kit as I worried the paint would just flake off, or perhaps block the return pipe, etc. Anyway, in the end I used caustic soda to get rid of the tar and then a rust remover from Bilt Hamber called Deox-c, and that really did a great job. Ok, it doesnt have any paint over the metal but I'm just going to keep it filled with fuel and hope for the best!

I couldn't find anyone locally who would refurb it professionally for me.

It would be great if someone would make an aftermarket fuel tank for our cars out of plastic. Most new cars come with plastic tanks and you'd never have rust problems again!

[Squiggle Dog]

I wonder if these could be hot tanked like a rusty car body to bring them down to clean metal.

[oversize]

The main issues here are flaking rust and sediment which can be fixed by removing the tank and giving it a good clean with a hot pressure washer.  Then you need to get it dry.....

Then you have to deal with the fuel going off (approx. 3 months) and becoming acidic, plus moisture in the tank.  Keep using the fuel and put in a bottle of metho every so often to keep the water at bay.

Does anyone know if the inside of the tanks were originally treated, or just bare metal?

[s class]

I have dealt with a lot of W116/107/123, and the tanks appear to me to be zinc plated inside (at least for these South African built cars).  Most tanks I see are as-new inside.  The only ones that I have rust problems with are usually ones that have previously been subjected to 'professional' cleaning processes.  I always end up replacing them.  At least, here in in-land South Africa, good rust free tanks are relatively easy to come by. 

[ptashek]

The tank in my 350SE looks like new inside, and it also appears to be zinc plated gold on the inside, including the filler pipe. Maybe this was a Europe/SA thing?

Also, in Europe at least, a W116 tank in good nick costs upwards of 600EUR...
Crazy money.

[wbrian63]

I asked Tom Hanson, of the Mercedes Benz Classic Center in California how much a new tank costs, assuming one is available.

Sit down and consider they are still available - $2470.00US. With MB Club discount, I could have it at my door for $1975.00.

I asked if it came with a car attached...

[NormW116]

I thinks its more of a problem with cars that have sat for a long time, particularly with little petrol in the tank. I'm always reading how fuel tanks should be full when storing a car over winter for example. I think there is some sort of stabilizer you can buy to stop the fuel going "off", but no idea if it's any good.

[arcijack]

i cleaned my tank out with a 50/50 acid mix, the tank looked new, i used a product called red kote and its been almost 3 years, absolutely no issues, tank looks just as good as the day the car was bought, the car sat for 16 years, and it had everything imagianable in it, trust me if done correctly , you will have no issues, the key is sealing off the lines so the coating can't migrate to lines

[arcijack]

if that don't work i know a gentelman here in Mississippi who can cut it open and restore the tank better than factory and i promise yopu it will never rust again, i state my life on it. he is a genius