MerCruiser 4.3

Each day, before starting

• Check the crankcase oil level
• Check the sterndrive gear lube level
• Check the trim pump oil level
• Check the power-assisted steering pump or compact hydraulic steering fluid level, depending on your steering system

Each day, after use

• If operating in salt, brackish or polluted water, flush the seawater section of the cooling system after each use

Weekly

• Check the water inlets for debris or marine growth
• Check and clean the seawater strainer, if equipped
• Check the coolant level
• Inspect the sterndrive anodes and replace if 50% eroded

Every two months or 50 hours, whichever comes first

• Lubricate the propeller shaft and retorque the nut (freshwater-only use may extend this to every four months)
• If operating in salt, brackish or polluted water, apply Corrosion Guard to the power package
• Check the battery connections and electrolyte level
• Check that gauges and wiring connections are secure, and clean the gauges

Once, after the initial 20-hour break-in period

• Change the engine oil and filter
• Change the sterndrive gear lube
• Touch up the paint on the power package

Every 100 hours or annually, whichever occurs first

• Change the engine oil and filter
• Change the sterndrive gear lube
• Replace the water-separating fuel filter element
• Retorque the connection of the gimbal ring to the steering shaft to specification
• Check the steering system and remote control for loose, missing or damaged parts; lubricate the cables and linkages
• Check the continuity circuit for loose or damaged connections, and test the MerCathode unit output on Bravo models
• Clean the flame arrestor, the IAC muffler (MPI engines) and the crankcase ventilation hoses; inspect the PCV valve if equipped (on V6 models the PCV valve is a non-serviceable internal part of the valve cover assembly)
• Inspect the condition and tension of the belts
• Check the coolant level and antifreeze concentration for adequate freeze protection
• On driveshaft extension models, lubricate the driveshaft U-joints and the tailstock input and output bearings
• Touch up the paint on the power package

Every 200 hours or 3 years, whichever comes first

• Inspect the U-joints, the splines and the bellows, and check the clamps
• Check the engine alignment
• Lubricate the U-joint splines and cross bearing, if equipped with a grease fitting
• Lubricate the gimbal bearing and the engine coupler

Every 300 hours or 3 years, whichever comes first

• Check the engine mount for tightness and retorque if necessary
• Check the distributor cap, if equipped
• Check the electrical system for loose, damaged or corroded fasteners
• Check the cooling and exhaust system hose clamps for tightness, and inspect both systems for damage or leaks
• Disassemble and inspect the seawater pump, replacing worn components
• Clean the seawater section of the closed cooling system; clean, inspect and test the pressure cap
• Inspect the exhaust system components and verify that the flapper valves are not missing or worn, if equipped

Every 5 years (every 2 years if extended-life coolant is not used)

• Replace the coolant

The 100-hour cadence is not the diesel 250-hour cadence

Owners moving from a marine diesel — or reading a generic maintenance article — routinely stretch the oil change on these engines. Mercury's schedule is 100 hours or annually, whichever comes first, and for most recreational boats the annual half of that is what actually fires: a boat used thirty hours a season still needs an annual oil and filter change. The drive lube is on the same 100-hour or annual cycle, and it is the one people forget because nothing about the engine reminds them.

Drive items and engine items are on different clocks

The bellows, U-joints, gimbal bearing, engine coupler and engine alignment sit in a 200-hour or three-year bucket that has nothing to do with the engine service, and the seawater pump lives in a separate 300-hour bucket. Because these are drive jobs rather than engine jobs, they are easy to skip entirely for years. A split bellows sinks boats; the gimbal bearing and coupler are labour-intensive to reach once the drive is off, so they are worth doing together while it is out.

Where the raw-water pump lives depends on your drive

On an Alpha the raw-water pump is inside the sterndrive, so servicing the impeller means dropping the drive. On a Bravo the seawater pump is mounted on the engine and the drive is not involved. This changes what the job costs, who does it, and which parts you order — and it is the single most common source of ordering the wrong impeller for these engines.

Anode guidance has moved on from the old zinc rule

The familiar advice is magnesium for fresh water, zinc for salt. Mercury no longer publishes zinc drive anode kits at all — their current range is magnesium for freshwater use and aluminium rated for both fresh and salt, and their aluminium anodes are described as superior to zinc. If you are replacing anodes on a drive today, the practical choice is magnesium or aluminium, matched to your drive family. Individual zinc pieces still exist for some fittings, but they are not the drive kit.

Mercury serves the correct Operation, Maintenance & Installation manual against your engine serial number. Because these engines span many model years and two drive families, pull the manual for YOUR serial rather than relying on a generic revision.

Mercury lists the engines this filter does not fit — check the exclusions against your engine.