On a 126 car, I lay an old sheet along the back in the section between the battery and fuse box. No sense in getting this wet. I believe you could do something similar with some of the 124 cars as well.
I live about 150 yds. from a car wash, so I don't have to worry much about washing too hot of an engine. You can crack the exh. manifold if you spray it when it's too hot.
I spray it first with the detailing rinse water, then spray with the engine cleaner. After that, I switch back to rinsing with the detailing rinse water.
I think what sometimes causes trouble is careless use of the full-power cycle. This setting may knock crucial ign./elect. stuff loose.
My 2 cents.