I am replacing the water pump, flushing the coolant system on my 2000 Blazer LS. So i thought i would clean the expansion tank as well since the tank was so dirty and had a lot of dark brown/black rust water spots and "what i think is" Dex Cool residue

First i tried vinegar, orange acid, baking soda, coffee, and different combinations of this products mixed together with without getting the tank clean

Since none of the products above worked when i tried to clean the expansion tank i was thinking of buying a new tank since the one in my car looked so bad.

I decided to give it one more try using kerosene and that really worked well

So if any here is going to clean the expansion tank i suggest to use kerosene to clean both the inside and outside

I did not take any pictures of the tank before i cleaned it but here is a couple of pictures after i spent an hour cleaning the tank

 

Looks good

 

The insides are so hard to clean because of the many baffles inside. If someone had an old one they could cut in half, you would see the many baffles. They are hard to clean with just detergent and water pressure from a hose. The brown sludge seems to stain the white plastic.

 

We have cleaned plastic humidifier tanks here at work that have turned red on the inside (iron deposits?) with Alka Seltzer tablets. It cleans them pretty good, almost looking like new again.

 

Yea looks good. That dex cool **** really got me in the wallet, couple years after a got my 99 the heater wasn't working and I look in the radiator and saw that dex cool **** all sludge up. Took to a shop they had to replace the radiator and flush the hell out of the entire system. After that the guy said I could run the green prestone from now on. All these years and miles later haven't had a problem since.