YES! Acid into water, NOT water into acid. The reaction between the two can be exothermic (gives off heat) enough to cause the water hitting the acid to flash boil and blow the mix into your face. I use muriatic in concrete work and to adjust pH in swimming pools. Home depot. I would use it at no more than 3:1 dilution. Have some baking soda around to neutralize the acid.

Radiator shops use a strong alkali solution to clean radiators. Lye is a strong alkali. It also eats eyes up...

well I tried several things,
lye
***** n span
foamy coil cleaner ( a product sold in refrigeration supply house. It is an alkali cleaner and strong stuff.)

After each soak I checked to see what came out. Believe it or not, the ***** n span seemed to work best. Each time it would loosen some rust colored junk

This was an aluminum plastic for a small car... not even an
factory part. It was the only one I could find in the yard.

I will try lemon juice next ...to get the soap smell out.

okay for some reason the second product is a cuss word!
A household cleaner:

S P I C n span

I did the muriatic acid and wow does it work good. My radiator looks new on the inside now.

I filled the rad i would say 1/3 with water and then with muriatic acid and let sit for 15min. then I flushed really well with a water hose and shaking as best I could. Then repeat. The acid does a number on the paint on the outside though so i just repainted it with some black high temp paint.

I will post back and let everyone know how it works out for me.

I can chime in with a bit of scientific background here. I worked in a test lab last summer and did a lot of work with corrosion. For rate tests we needed to mix up a solution that would eat away the corroded material but not the base metal. So if you ever want to clean rust off of your steel, mix up some Hydrochloric acid with stannous choloride and antimony trioxide- 100ml, 5g, and 5g. That will eat iron oxide but not iron/steel.

Guess what we used for copper? 1:1 HCL and water. It will consume copper oxides but not copper. So mix up HCL (aka muriatic) into water and use there. 1:1 is probably a bit strong for radiator cleaning- when I dropped a copper test coupon into a dish of 1:1 HCL:water, it became clean bright copper within about 2-3 seconds. You probably are more patient than that, right? You'll do fine with a weaker solution.

Keep shaking & hosing it out, till you see NOTHING comming out but water.

Ed

Hey Ned, Was your testing work done at IMR?

Did you work with aluminum too?

For those who used water diluted HCl, what did you do with the 'dirty' acid water solution? I assume this is not something that should be drained onto the ground, lawn, or sinks/sewers right? Here in the bay area, many of our drains go directly to the bay so we have to be extra cautious with what we allow to drain there.

I had some gardening lime that I used to neutralize it. Once the fizzing stopped I poured it down the storm drain. Just go to your home store and buy some lime and add it to the used up water/acid. I had a 10 gallon bucket of water/acid mix of which was only about 1/2 gallon of acid. Most of the water came from when I flushed the radiator out. I used probably 3 cups of lime.. not sure exactly since I did not pay that much attention.

I just did a search on how to dispose of it and found that suggestion.

Yes, I worked at IMR. I had an internship there for the summer of 2008. I did do some work on Al, but mostly steel and Nickel superalloys. The corrosion work I did was all steel and copper, though. I'm not sure what solution one would use for an Al radiator. Al is different from steel and copper in that pure aluminum is very susceptible to oxidization- what prevents it from flaking away like steel does when it rusts is that the density of aluminum oxide is not very dissimilar from Aluminum, so it doesn't heave up and flake off like iron oxide does. So the aluminum oxide forms a protective barrier.(For more reading, google Pilling-Bedsworth ratio) Some things will penetrate this aluminum oxide barrier, though- mercury and gallium, both of which are severely restricted for air transportation. If they came into contact with the aluminum airframe, severe damage could result as the aluminum oxidized away with no protective layer.