Should your engine be on while washing it or not?

Shut off and warm. Cleaning the engine compartment is not that difficult and unless you are a perfectionist or plan to enter the vehicle in Concours d'Elegance competition, it does not require much elbow grease. First, warm up the engine for a few minutes. This will help soften the grease and crud. However, do not let the engine get hot. Never spray water on a hot engine since sudden temperature changes can cause serious damage. Also you can get serious burns from hot engine parts. Next, cover critical parts of engine with plastic bags and rubber band to protect them from water and other liquids. Either cover the air intake and filter or remove it and cover the opening. Protect electrical components like distributor, coil. alternator, and fuse box. Use rubber bands to seal the bags around the components. Check the oil filler cap, the power steering filler cap, oil dip stick, etc. to make sure they are tight. After everything is sealed up, spray the engine, accessories and surrounding components with a high quality non-petroleum-based degreaser that will not harm the paint. After letting the degreaser work for about five minutes, use a soft brush, a paint brush works well, to loosen up the crud. Respray with degreaser and rebrush if grease and grunge remains. When the entire engine and engine compartment looks pretty clean, rinse with lots of water from your garden hose. If you can, hook up to a hot water tap since hot water will do an even better job. Better yet, do the job at a do-it-yourself car wash which usually has higher pressure hot water and is set up to handle the dirty water in a more environmentally friendly way. Even though the degreaser may not contaminate the ground, the nasty stuff washed off can get into the groundwater supply and do harm. Many car washes have equipment specifically for cleaning engines. If you want to use a degreaser that you know is safe, I only use the facility to rinse with plain, hot water. Clean the engine first and wash the vehicle after cleaning the engine compartment making sure all overspray of the degreaser is removed. Since all degreasers will remove wax, plan on rewaxing after cleaning the engine compartment. Once the engine and compartment is clean, immediately remove all plastic bags and rubber bands. Dry standing water and aluminum parts with a soft cotton towel. Start the engine and let it to warm up to dry the rest of the engine as well as evaporate any moisture that may have collected in electric parts. If you do not start the engine immediately, often moisture will seep inside parts and it now will take a long time for things to dry out. If this occurs, use an ordinary hair dry to heat ignition systemparts like distributor and coil. Once everything is dry and has completely cooled, you may want to coat hoses, weatherstripping, shields, gaskets and other rubber parts with a rubber protectant. However, do not use it on rubber belts since it could cause them to slip.