Hi there folks, I have used this product (OIL EATER) and am amazed with the results. I stuck a dirty head in a bucket of this stuff and left it over night and it came out quite clean. Perfect for cleaning very dirty engines..In my opinion , it is the best degreaser I have ever used. Costco used to sell it...may have some in a Costco near you. Here is the link.
http://www.oileater.com/CleanerDegreaser.html

 

Awesome. WE also have some Zep 50 Engine Degreaser that works well also. WE just let the engine idle up to operating temps, spray it down VERY liberally, let it sit 5-10 minutes, and hose that bad boy off....It'll make a leaking 25 yr old diesel mercedes motor look like it just rolled out of a showroom.

 

Zep makes good stuff. We use Zep Big Orange the same way at work, and it also makes old junk look like new!

 

Castrol's Super Clean works very well for cleaning engine bays. I use it on my tires too to really make them look nice...