Are you cleaning the whole engine bay? The best stuff to use all over is TFR (Traffic film remover) You can either buy 5 litres or 25 litres that will dilute to 25 or 100 litres (it will last ages).
I use it on bodywork, wheels (its not aciddic so wont harm), door shuts, engines anything really. Just spray on using a 5 litres pump spray, leave to soak or brush in and rinse.
:wink: