Pre-spray the whole engine bay area with either a diluted all purpose cleaner or a designated engine cleaner degreaser and allow to dwell.
Work in the cleaner with a soft bristled detailing brush. Pay attention to the actual engine block itself, working the cleaner into any rocker cover details and around any oily or greasy areas.
Use a clean soft bristled detailing brush to clean the actual underside of the bonnet or hood, working around the catch area and other panels if necessary.
Rinse off the engine bay at low pressure ensuring no water is driven into sensitive areas.
Using a clean dry microfibre towel begin to dry the engine bay. Spend some time ensuring all moisture is removed and that all areas are covered. Once the engine bay area is dry move onto drying the underside of the bonnet or hood.
Once all areas are sufficiently dry you can remove the protective shrink wrap or cling film you applied earlier on.
Spray a designated dressing protectant product onto the main plastic areas of the engine bay then work in with a microfibre or sponge applicator pad. Use a clean soft bristled detailing brush to work the dressing into awkward areas.
Apply the product directly onto the applicator pad and work into rubber hoses and piping. If necessary, buff off dressed areas with a clean dry microfibre towel to remove any excess product.
Polish any metal or chrome areas. Clean up the area with a fine wire wool first if necessary, then apply polish using a microfibre or sponge applicator pad.
Finally, buff off any residue with a clean dry microfibre towel.