A general Mercruiser service schedule is based on engine hours or annually, whichever comes first. The schedule can vary by engine model and operating conditions, such as use in saltwater. 

Initial 20-hour service
This service is typically performed on new engines after the first 20 hours of operation. 

• Inspect the engine and accessories for damage.
• Drain and refill the gear housing with appropriate gear lube.
• Change the crankcase oil and filter.
• Lubricate all grease fittings, splines, and couplings.
• Check all fluid levels and belts. 
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Annual or 100-hour service
This service is recommended once per year or every 100 hours of use, whichever occurs first. 

• Change engine oil and replace the oil filter.
• Drain and replace gearcase lubricant.
• Replace the fuel filter or fuel/water separator.
• Lubricate all grease points, including the engine coupler and drive splines.
• Inspect and test spark plugs, replacing as needed.
• Check all hoses, lines, and electrical connections for damage, leaks, or corrosion.
• Inspect the condition and tension of belts.
• Check the battery and its terminals.
• Inspect corrosion control anodes, checking more frequently in saltwater. 

Extended service intervals

• Every 200 hours or 3 years: Complete drive service, including lubricating U-joints and splines, checking bellows, and inspecting engine alignment.
• Every 300 hours or 3 years: Check engine mounts, inspect cooling and exhaust systems, and replace the seawater pump impeller. An impeller replacement every 100 hours or 2–3 seasons is also recommended, especially in saltwater.
• Every 5 years: Replace the coolant or antifreeze. 

Important maintenance tips

• Harsh conditions: If you operate in saltwater or high-performance conditions, you may need to service your engine and replace the impeller more frequently.
• Check gear lube for water: When draining the gearcase lubricant, check for a milky color, which indicates water has entered the gear case and requires further inspection.