I use a lot of the Advance Auto brand "heavy duty degreaser" Smells about like diesel fuel, but it works pretty good for cleaning up engines. If you can hook up a hot water hose with a high pressure nozzle, that will also help things along.
I've also got some car wash brushes I picked up at some box store- one's a stiff bristle that's good for scrubbing down the fins.
I recommend the elbow grease method- even if you were to blast it afterward, you would want all the grime you can get off of it.
Alternate method would be to take it to your local car wash and go to town on it. That's a pretty cheap way to get a hot water pressure washer.
