How To Clean, Whiten, and Restore a Coolant Overflow Tank

Here’s a tutorial video showing how to clean and whiten (remove the yellow color) coolant expansion or overflow tanks.

The coolant overflow tank was sitting in this car for far too long and it was simply horrible with a ton of 30-year-old sludge, dirt, and discoloration. Good quality replacement coolant tanks for this car, an ’87 Toyota MR2 don’t exist, and used ones are usually in similar condition.

After researching how to clean an overflow tank and get it looking like new again.

Cleaning the inside was fairly easy with some common household items; some rice, bleach, a dishwashing tab, and a lot of shaking gave results that are were better than expected.

The outside was scrubbed with a dishwashing pad and a bleach and water mixture. Again, the results were decent and 30 years’ worth of dirt was gone in mere minutes.

The tank is clean, but still yellow…

What was annoying me most of all and where it was the hardest to get the results was the yellowness of the coolant tank.

Scrubbing is dead useless here — the yellowness you see on coolant tanks is the result of a chemical reaction. The only solution is to whiten/bleach out the ugly yellow color out of the coolant expansion tank. However, this is a lot easier said than done.

Initial research led to a solution called Retrobright (aka Retr0bright), a chemical mixture used to remove yellowing from acrylonitrile butadiene styrene (ABS) plastic computer and electronics cases, including computers by Commodore and Apple in the 1980s and 1990s, and various video game consoles and cartridges.

A batch was mixed, but the results were extremely poor. However, this little experiment led to the key ingredient to getting my coolant expansion tank white again — hydrogen peroxide.

The product with the highest concentration of hydrogen peroxide I could find was in hair-care products for bleaching your hair. On the same aisle, I found another product that promised to add an extra kick of aggressiveness into my bleaching formula, it was called bleaching powder and when mixed with the hydrogen cream it promised extra bleaching power.

I stocked up and got to work. Results finally started to appear. After several bleaching sessions with the inside and outside of the coolant tank covered in the bleaching solution, I managed to get most of the yellow color out…

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