but it really depends on how dirty your engine bay it, if its really sludged up then steam isn't gonna shift it, just good old elbow grease 
If it is really stodged up, then a steam cleaner is the
very thing that you want. NOT a cold water pressure washer, but a steam cleaner - cuts right through it leaving it 'squeeky clean' if that is what you are after.
That said, a plain old pressure washer will cut through the muck and leave an oily surface and dirty oily marks - which can be a good thing; the steam cleaner does get it very clean, but then it is so clean that it will start to rust....
I gave up using gunk years ago, pointless stuff. Get a pressure washer of somewort on it. Leave the engine runing and the heat from the engine will dry it out. Worst the generally happens (as long as you are being careful) is that you may need to dry the cap and the leads off.
Edited by sixwheeler, 24 February 2009 - 04:30 PM.