Maybe you could have problems on an older car but if you unplug the coil on a recent car you will see some quite good sealing and like I said, I wouldn’t dwell on anything really. I’m not telling people to wash their engines, only that I do and I’ve never had any problems. I probably wouldn’t wash a hot engine but warm does help dry it quicker and I do sometimes go round with the compressed air blow gun and knock the standing water off any little reservoirs. As an example of what can be done, I bought this 9 year old Yaris for my daughter and it had been used like most people use a car - as a means of getting from A to B. We started by washing the outside (BTW, thats my immaculate 2016.5 that got stolen in the background).;
The rear bumper went to the paint shop for a small repair and that is a good opportunity to clean behind;
With the front seats out, you can see the grubby carpets;
The carpets are backed with plastic and moulded to shape. You can get them out but everything including the console and rear seats have to come first so best is to leave them in and get them wet;
There was a time when the trim would fall off a door card but these modern door liners are so well made, they can stand a good wetting;
The seats too only come really clean when water and suds become the medium to carry the dirt out so again, bath time!;
Then a powerful vacuum to pull the bulk of the moisture out;
and then after the carpet gets the same treatment, things start to look much better;
......and with the seats back in, it starts to look somewhat better;
The engine was absolutely black with dust and spilled oil. It will never come perfect as the aluminium has oxidised a bit but again, with no protection what ever, a soak with TFR the pressure washed;
At the end, it was quite presentable for my daughter.