Carburettor non electronics engines, pressure wash is mainly good. The wash should not be pointed directly into bearings, seals. Oil sludge collects dust /obstructs cooling causing untimely engine/tranny wear. My cleanup: hot engine, first sprayin dissolvent onto just about every place(diesel fuel or whatever non too aggressive solvent) after 15 min, before it dries, the wash.
The alt benefits from special wash:
http://www.cardomain.com/ride/748507/23
Low voltage signal paths in computer controlled vehicles cant tolerate 'any' water (luckily most bits are well shielded). Pressure wash is precipe for incredible pain - still has to be done sometimes. As water gets into components which may never become dry, resistance changes via water can cause intermittent problems for next 6mths depending on ambient temp humidity plus variety of variables. I washed my engine 4 yrs ago, check out the TPS circus...
http://www.cardomain.com/ride/748507/6
As my 80k engine doesn't leak at all (yes, cam/crank o-rings replaced), I dont wash it with water but use pressurized air, rags to clean. Maybe sometime in future it has to be washed, I am afraid. Then I'll try to shield any electrical components (not alt), try not to point the pressure into x components (next to impossible). My son has to wash his awfully dirty engine once a year at my garage (yes, eurobean Citroen, leaking like all healthy GM's) - and so far has successfully driven home with the clean engine
Maybe he is lucky (with a citroen!?) or I am unlucky. One has to try.