Simple Green does work, but needs agitation to be effective. It also needs to be rinsed with water, so this time of year that might be challenging. If you leave it on the car, it will etch and discolor aluminum.

I use the foamy engine degreaser from the auto part store. Collected as much as I could in my oil catch pan and dropped it off on one of those household hazardous roundup days.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles