Parts Cleaning

[jimbbski]

What's the best way to clean the scale out of the water passages in aluminum rotor housings or engine blocks? Someone else recommended oven cleaner (basically a stong base like lye) but that it turns the aluminum a dark gray. I need something that will not eat at the aluminum or chrome.

As you have found out oven cleaner is not for use on aluminum. Most anything else it works fine. What I have used on aluminum is the paste type paint removers. It will take off carbon and soften old or hard grundge. The sort of stuff that normal mineral sprits don't work well on or takes a very long time to remove, and only it you keep it "wet" or soak it. On larger parts that may not be an option. I often cover the part with the remover on it with plastic wrap to keep it from drying out while it works. Follow the directions on the can of remover to clean off the part.
On water passages a mild acid may clean that deposts. The acid to use is the type contained in the rust removal product called "Naval Jelly".
What is contains is Phosphoric acid. You can buy it in liquid form by the gallon at most home improvement stores. Usually less then $15 a gallon. You then mix it 1 part acid to 4-5 parts water. You will find it in the paint section usually labeled as concrete cleaner/rust remover and sometimes as aluminum cleaner. Do not confuse this with Muriatic Acid. That is not what I'm talking about. Muriatic acid will eat up aluminum, even in weak solutions, howeve is does make a good rust remover. Body shops sell a solution labeled as"Metal Prep". It is used to clean bare steel pyror to painting, I believe it contains the same Phosphoric acid.