I'd be careful using an automatic wash to flush the chassis in the rust belt. They are notorious for recycling the soapy wash fluid, resulting in a salty brine. This would be the equivalent of efficiently forcing seawater into all the nooks and crannies of your vehicle! I heard the rinse water is fresh though.

My tip: If you live in the rust belt, buy yourself a pair of rubber gloves and keep the garden hose indoors. Anytime the outside temperature is above 32° you can wash your car and flush the salt. I've been doing this for 30 years and saved a lot of money in that time. I get strange stares from neighbors who watch me washing my cars and snow is piled high around the driveway. But this is when cars most need to be washed. Surprisingly, hands don't get that cold with rubber gloves on. Further tip... if you're washing the car late in the day and it's barely above freezing, the doors will surely freeze shut unless you keep the doors ajar for 10-20 minutes after washing. This'll allow most of the water to run off rather than wick into the door seals and freeze.

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95 E320 Cabriolet, 169K