The problem with freeing an engine with fuel is that it's expensive. At $25.00/gal for fuel, enough to immerse an engine is more than I would like to throw away. Anti freeze, on the other hand, is much cheaper, and it will not turn an engine dark gray if the temp is kept at 250 or below. And it can be used over and over. It will do the job and, contrary to what a lot of people say, it doesn't seem to affect rubber seals. Consider that fact that in a car water pump seals are running in hot anti freeze all the time and they are not damaged by it. I keep a pot of anti freeze at all times and when I pick up an old engine with lots of crud both on the inside and the outside, I simply pull the back plate, remove the glow plug and needle valve and dump the entire engine in the anti freeze. I let it heat for several hours, remove it and flush liberally with water, then blow it dry with compressed air. Some of the really crusty engines will require some light brushing with an old tooth brush after the engine comes out of the solution and then flushing with water again, but it gets both the inside and outside of an engine looking like new with very little effort.