You'd be surprised how little cutting power you need from your cleaning solution if you just gets a good brush in there while you are cleaning the engine.

Use Eagle One aluminum wheel cleaner for coated aluminum surfaces, and use Eagle One chrome wheel cleaner for any strong bare metals, and bare aluminum, and of course, chrome.

Oven cleaner is a good cleaner for old engines composed COMPLETELY of steel and iron. if you have some old box that you just want to clean out good, that will do it. I would not use it on anything resembling a modern Mercedes. Oven cleaner will also take off most kinds of paint as well.

But my favorite of them all is the steam cleaner. It's safe, noncasutic, it isn't hazardous to breathe, and it's easy as all hell to use. It's frickin water people. Use it on anything.