With all the mini computers in cars its common knowledge not to hose off the engine. One drop of water can short out a $400 to $1200 mini computer.
But using the undercarriage wash option at automatic car washes does the same thing. Its even worse because the pressure is a lot higher than a garden hose.
Car washes have high pressure jets that spray up under the car. The jets blast water all over motor up to the bottom of the hood. Just raise your hood after you go though a wash to see the proof.
The argument is that if the car is in good shape that wont happen. BS: there is no perfect car and any car can have a crack or gap in a wire or seal.
After every snow people line up at car washes to rinse off the salt and road grime from under their car. They may as well get garden hose and blast their engine.
I know its a trade off: salt under car vs car dying on road, calling tow truck, and some mechanic telling you that the computer is not working and that the bill will be over 1,000.