I just swapped out my DexCool for Prestone on my 98 LeSabre. As I have seen on many of these cars, the inside of the plastic overflow tank was coated in some kind of rusty-looking gunk leftover from the DexCool.

I wanted to get that junk out of there, so I removed the tank for cleaning. Lacking a bendable bottle brush to scrub that crap out, I tried "swishing" all kinds of cleaning solutions in the tank: Simple Green, vinegar, bleach, baking soda, ammonia, rust remover, mineral spirits, carb cleaner...none of that worked. Someone in another post mentioned brake cleaner, but I didn't have any on hand.

Finally I tried a concentrated solution of Oxi-Clean...the gunk disappeared almost instantly.

Just a tip for any who don't like gunked-up overflow tanks.

Awesome to have a better way. thanks

(checks bucket next to washer...yep..oxyclean)

simple green and a rag stuffed in there worked great for me

Yes that'* what I do every year.
stuff a cleaning rag inside with some simple green and holding the bottle closed shake it around and do the dance.

It works for a lot of stuff.



good for cleaning an engine too.

Billy Mays pulls through again!!! Thanks for the tip!
Isnt' Dex bio-based? Could that explain why Oxi-clean can take care of it so easily?

the brown residue is NOT from the dexcool itself. In the last ten years GM started using coolant sealant tablets to help prevent minor coolant leaks, and to close off leaks that do form and are minor. The coolant tablets leave a brown residue like you're describing and many GM dealers have stopped using them because customers confuse the residue from the tablets with rust. To avoid the hassle of customer'* being pissed off after a coolant flush, many have just stopped using the sealant tablets all together.

Thanks for the info.

I knew it wasn't rust, because neither sulfonic acid (rust remover) nor vinegar did a thing to it. All I knew was I wanted that junk gone, and Oxi-Clean worked.

Wait, let me say it like Billy Mays...

OXI-CLEAN WORKED!!!!!!!

I use rock salt extra coarse with a little water and shake violently. Works like a charm.

So if I understand that, it means that GM tried to correct a design deficiency by adding the sealing tabs but due to ignorance have discontinued in spite of the leak risk.
Bad GM again.