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Old 11-24-2019, 12:14 PM
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funola funola is offline
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Join Date: May 2005
Location: NYC
Posts: 8,243
I have cleaned a W123 tank before and have cut one open to look inside. W123 tanks are quality tanks made from good metals with some kind of Terne coating inside and out that's resistant to rust.

Here are some recommendations if you are going to clean one:

1. Make sure the vents are not blocked first. Unblock it if it is blocked . Do not use any kind of tank sealers unless you are able to keep the serpentine tank vent tubes from being closed off by the tank sealer.

2. Take the tank out. Mount it to a long pole as if you are doing a pig roast. Support it on 2 forked tree branches driven into the ground. Attach a crank so you can turn it.

3. Put in a few hand full of round beach pebbles or ball bearings that's slightly larger than the vent opening, together with a gallon of good degreaser + hot water (follow recommended product mix ratio), close off tank openings and crank away. It helps to have a borescope so you can look inside for a before and after. Repeat as necessary.

If after the de-greasing, and you still see rust, repeat step 3 with phosphoric acid solution.

Rinse well with water then final rinse with hot water. Dry it off quickly with compressed air, or a leaf blower.
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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