I have come to the conclusion that it just isn't safe to clean our engines...
That's it... They are made of bare aluminum and washing w/ any kind of solvent may lead to etching, dulling and so on...
Read on~

I just spent three hours at Advanced Auto, O

 

since i have cleaned many engine bays, including those with aluminum, i can give you my thoughts-
but you pretty much hit on the idea- use a non-acid based cleaner.
p21s is one example, which you mentioned...
and the method is just about as important as the products used-
you need the engine to be warm but not too warm- i start the car and drive it down the block and back at the most. bring it back, open the hood, assemble the products and go at the cleaning-
btw, here is a good thread on the "how to" side of the job:
https://www.s2ki.com/forums/index.php?showtopic=278999

 

Excellent post and excellent use of