Maintaining a clean engine is an important aspect of keeping its various systems running properly at all times. Different systems have different requirements for maintenance and, in order to ensure that they run properly, keeping things clean will ensure they continue running right.

Weekly

Warm the engine for 1 to 2 minutes so that debris can be loosened. Brush away loose debris and dirt from all surfaces with a paintbrush with stiff bristles or with a cleaning brush with plastic bristles. Brushing grime and debris away on a weekly basis will prevent buildup that can cause further harm to the engine.

Monthly

Clean the engine compartment more thoroughly on a monthly basis. Remove both the negative and positive terminal cables on the battery in the engine. If there are any exposed electrical components, they should be covered thoroughly using plastic wrap or a plastic bag. Cover the air intake and carburetor with heavy plastic or aluminum foil. Mix a grease-cutting type of dish soap with water and scrub the engine with a brush before rinsing using a garden hose. Cleaning grease and other debris this way once a month will slow down the build up over time.

Annually

Annually, take the time to perform a more serious cleaning of the engine compartment of the vehicle. Consult the vehicle's service manual for insight into what materials will best suit the cleaning of the elements of the engine. Some metal parts that are coated with a heavy grease may best benefit from the use of mineral spirits or a similar solvent. Most auto supply stores will stock a heavy engine degreaser that will be effective.

Source:

Proper Auto Care