Martha Stewart writes....
"Is there any practical reason to clean the outside of the engine?"
Yes, a clean engine is a happy engine.
I know a guy who runs his own trucking biz with some Kenworths
and pressure washes his engines regularly so he can catch
any leakage needing repair, right away.
Two main reasons I like to keep my engines clean:
* You see leaks or anything loose or out of place, more easily.
* Nice to work on clean stuff, sockets go on nicely on clean bolt heads
etc. Its a luxury to work on clean stuff but you can have that luxury
with your own stuff if you clean it once in awhile.
I have always washed my daily drivers' engine regularly for years
at car washes, for the same reasons above.
If you like mechanical stuff, dont you want to open the hood of your
rides and see all the details of the mechanicals, rather
than just a big black oily dusty mess?