Dayum. You mean "engine shampoos" are legitimate?
My all-time favorite Car Talk episode was a guy who called in after taking his car to one of those "Quick Lube" places where they charge some insanely low price for the oil change and then find a lot of expensive things that need to be done. He said they sold him an "engine shampoo" and wanted to know if his friends who told him he'd been ripped off were right.
After they picked themselves up off the floor where they'd fallen down laughing, they asked if he'd gotten the conditioner, too. Bottom line: not necessary.
I've never washed an engine and don't believe I've ever had a mechanic do it, either. Now that I think of it, though, when I looked under the hood of the first car I ever bought (a 1973 Hornet, in 1975) at the dealership, it appeared nice and clean.