I've done this loads of times, hateful stuf, I hate it, I hate it!
Best I've found is with a hot air gun and a scraper - that will get the bulk of it off. Then wipe with rags soaked in whatever you find cheapest - white spirit, petrol, paraffin, spirit wipe, so long as it's oil-based stuff, don't use celly thinners for example as it'll take the paint off too.
Then finally put a tray underneath to catch the excess, and "wash" it off using the spirit cleaner and a long-haired paintbrush.
When you've done that lot you'll never use the stuff again yourself, as it's such a pain to get off, and doesn't do a great job of rust prevention either IMHO - use stone-chip paint for that!
Why do people put this stuff in engine bays? Nuts!

Some people are like slinkies - they serve no useful purpose, but they still bring a smile to your face when you throw them downstairs.