Maintaining an inboard boat engine is much like keeping a car engine shining. Part of the maintenance process is cleaning the engine bay to remove grease and grime buildup. Keeping the engine clean makes it run cooler and extends the life of gaskets, hoses and parts that are susceptible to corrosion. Just like a car engine, cleaning an inboard boat engine takes time and hard work.
Pull the boat out of the water and tow it to a location where chemical runoff from the cleaning process won't pollute the waterways.
Place a large bucket or barrel below the water exit points in the engine bay to catch the water and chemicals used in the cleaning process. Open or remove the inboard engine cover to make room to work. Bring all of the supplies onboard and place them within easy reach while you're working in the bay.
Cover the fuse box, distributor cap, ignition and any other electronic parts. Use old grocery bags secured with a rubber band to minimize water and chemical exposure.
Spray on the degreaser and let it sit per the manufacturer's instructions. Use a screwdriver to remove heavy dirt and grime deposits while the degreaser does its job.
Hose down the engine bay with water to remove the initial coat of buildup. Use a metal brush against metal areas and a soft toothbrush around gaskets and hoses. Remove the chunks and blobs that have fallen to the bay floor with a shop vacuum.
Put another coat of degreaser over the engine and wait for it to soak in. Use the brushes on the engine to remove the remaining oil and gunk and vacuum the floor out again.
Use engine polish to shine and protect the engine. The engine polish also creates a thin coating to help make the next cleanup easier.