I'm not a fan of driving water under force into anything in the engine bay. Too many plugs, gaskets, and joints in there that aren't supposed to be wet.

My SDL's engine was seriously grimy from years of leaking valve cover gasket (was still the factory one when I got the car). That stuff was like tar. I used a product called "Oil Eater" that I got off Amazon for cheap and its worked better than any other degreaser I've ever used.

Spray it on full strength with a pump up sprayer and wait about 5 mins then rinse off. Be prepared for a horror show under the car, I wouldn't do it on the driveway. It took 2 applications on my car and it was spotless. Big bonus point - it won't discolor aluminum like the purple cleaners or Easy-Off will.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]