I don't know if mine had special grunge on it but it LAUGHED at conventional cleaners (Gunk, Purple Stuff, etc.). I remembered that an old friend had recommended Easy-Off oven cleaner - not the environmentally friendly stuff but the old-fashioned formula (probably not available in CA). I suspect that the main ingredient is lye but I don't actually know that.

Anyhow, I did mine with the engine out of the car. Scrape off the part you can get to then squirt the Easy-Off on and let it sit in the shade for as long as the label directions suggest (I think it was 15 minutes). I hit it with the pressure washer and let it dry completely. I had to repeat the process to get everything off.

Even after this when I pulled the pan and cam cover I had to take them to the auto machine shop for a hot tanking before the powder coater could bead blast it and do his magic.

Like I said, mine may have had more - um - dedicated - goo than most but it was a STINKER to clean.

If you use oven cleaner with the engine in the car - PROTECT YOUR PAINT!!!! It WILL mess it up. I'd use plastic sheeting over the fenders and grille. Like others have said, be sure to plug the intake and protect the alternator (or at least avoid it).

That's my experience.......

Dan