[SupergasDil]

What's the best way to clean an engine compartment that has been greasy and oily for 54 years to the point that it's ready for primer ?

I've already cleaned the big stuff off.

[Toms bird]

I've used kerosene to start using a spray bottle to apply, then spray foam engine cleaners and power wash off. Now your ready to start wiping down with wax and grease remover before you sand. I'll use comet or ajax type cleaners with red scruff pads once I sand it using a small 3" da pad that fits my sander. Then wipe down again with wax and grease remover. You can't get it to clean, but I tend to go overboard.

[360Rocket]

I have a 5 gallon drum of brake cleaner and I use it in a brake cleaner spray bottle that I can charge with my air compressor. Its refillable and works like a champ!

http://www.eastwood.com/sure-shot-sp...FZQjgQodFosJ8w

[Bobalong]

What comes to mind is oven cleaner. Someone mentioned kerosene. Make sure it's kerosene OR easier to find is charcoal lighter fluid, preferably a name brand. The cheap ones smell like diesel fuel.
Brake cleaner . . . . . .and the best for last but the most expensive is statting fluid. That is the most awesome degreaser in the world. Remember not to blow yourself up with a cigarette, or dropped old school light bulb.

[ponchjoe]

I buy a big roll of thin plastic, remove the hood, cover the whole car, cut out the area and tape it to the fenders, cowl/lower windshield and front end. Remove the big chunks, spray it down with full strength Purple Power, pressure wash it off and repeat if necessary. Brake clean and a lot of rags and gloves for areas not cleaned with pressure washer. Wax and grease remover (real stuff not the citrus based junk) red scuff pad, wax and grease remove again and repeat as necessary. Typically the frame crossmember under the engine requires a lot of manual labor.

[mtnbktrek]

Wab makes this stuff called "the bomb" it is a grease remover I use it on our heavy equipment and tri axles. I spray area then use hot water pressure washer it completely removes everything you can spray primer and paint right after it dries. It is amazing and actually works great.
We have a cook brothers truck shop that carries it. They make a heavy duty degreaser but it will etch aluminum quick so I recommend using the stuff that says the bomb on it.