Re: Cleaning Out XJ6 Fuel Tank Rust

In alt.autos.jaguar OmberJag <[email protected]> wrote:
> In alt.autos.jaguar Abandoned Trolley <[email protected]> wrote:
>> On 16/05/2026 02:32, OmberJag wrote:
>>> I've got one of the rusty, gunky, fuel tanks out of my 1983 SIII
>>> XJ6 that I'm trying to get back on the road. The car runs from the
>>> other tank, but the pre-pump filter I fitted blocks up with rust
>>> after a few minutes running, so I've got to to clean that tank
>>> later as well. There aren't any businesses advertising fuel tank
>>> repairs anywhere nearby that I can find, so cleaning them will need
>>> to be a DIY job.
>>> 
>>> For removing the rust I can get some Sulfamic Acid for free (mixed
>>> with Sodium Bisulfate). Phosphoric Acid seems more commonly used,
>>> but Sulfamic Acid manufacturer websites say it works for rust
>>> removal too (10-20% concentration). First I'll spin the tank on a
>>> cement mixer with a chain inside to break off the big flakes of
>>> rust, of which there look to be plenty.

I couldn't find a way to mount it on my cement mixer, so I used a
reel for winding up wire instead and turned it by hand for 15-30min
each day for a few days.

>> If the flakes of rust are THAT big then its a surprise that the tank 
>> doesnt leak
> 
> After the rust is removed, I'm worried it might. I've poked around
> suspicious spots on the outside and it seems OK, but apparantly you
> can get tiny pin-holes that are otherwise plugged up by the rust.

No sign of leaks yet but trying to wash the rusty sludge out turned
out to be a major effort which took days with filling/draining and
spraying water, trying to dry out, sloshing lacquer thinner around,
blowing out with compressed air. By the time I got the sludge
mostly washed out, the moisture (in spite of my drying efforts) had
caused surface rust to return to most of the areas which had been
clear. It seems like starting again with the derusting at that
point would turn into a lifelong occupation so I'm going to refit
the tank and hope that once sealed up properly it won't keep
rusting enough to make the larger rust flakes which clog up the
fuel pump. I assume the acid turns into a similar sludge?

> Or the gunk. I spent some hours today painfully trying to scrape
> out the thick sticky black gunk that I thought I'd already drained
> out after softening it with laquer thinners, but there was plenty
> left disguised as metal by a layer of rust dust.

In addition to the rusty sludge it turns out I missed plenty more
of that black gunk which was in a big mat mixed with rust after
derusting and I had to spend more hours picking bits out the drain
hole with a wire. I think I'll have nightmares about black gunk.
Trouble was it looks just like the metal of the tank once there's
a layer of rust dust stuck to it.

> After more research I think I'll go for the washing soda and
> battery charger "electrolytic" rust removal method. The acid would
> eat away some of the metal too, which might leave a surface more
> prone to rusting again. Or so I gather...

The method does work fairly well and is very cheap. I read 10g
washing soda per litre of water, but the conductivity was so high
with 200L in the tank that I had the fuel tank in that it was
maxing out the current from my battery charger, so I had to connect
a high-wattage 1ohm resistor in series to avoid overloading. I left
it for a couple of days and it seemed to work. It worked well at
breaking off rust flakes with the bubbles, but that was pretty
frustrating to have the tank full of flakes of rust again after so
long spinning it with the chain then blowing it out thoroughly with
compressed air. Maybe all that preparation is a bit pointless?
Converting the surface rust to the black derusted finish worked
better on the side facing up than the side facing down (with the
tank laying flat). I couldn't turn it over though since the rounded
side of the tank would trap an air bubble.

The main issue is that final step of cleaning off the gunk, which
is trivial for the solid parts cleaned in the online guides, but
for a tank you can't get your hand inside to scrub out manually,
it's surprisingly difficult. Lots of brown stuff washes out, but
still leaves plenty stuck to the sides which you see when you
scrape something over them. I don't know if there's a better liquid
than water or lacquer thinner for washing it out? I guess if I
could bake it dry, but I only have a little electric heater I can
poke in, then blow it out with compressed air, and I'm not sure if
the prolonged warmth and damp air actually encourages re-rusting
before it dries (and you can't really tell when it's dry inside
anyway). Of course it doesn't help that the weather is also damp
here in Australia at the moment.

Overall I think my experience makes a good case for buying the
repro tanks. But since I've got things set up and learnt some
lessons I might still give the other fuel tank a try.

-- 
OmberJag's Jags:
1990 4L Jaguar XJ40
1986 3.6L Jaguar XJ40 (parts car)
1983 4.2L Jaguar XJ6 SIII