The Zep purple stuff from Home Depot (1 gal. Industrial Purple Degreaser-ZU0856128 at The Home Depot) worked great on my Jetski engine compartment. I'd try not to get too much on the exterior paint- and wear gloves- it's pretty strong!
Maybe kerosene? Is it to remove undercoat? Just my 2 cents: use as little as possible (or none), and don't hose it off, just use rags, to avoid poluting nearby streams.
