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Mercury Mercruiser Inboard Maintenance
Mercury Mercruiser Inboard Maintenance

Mercury Mercruiser Inboard Maintenance

Inboard and outboard engine maintenance share the important similarity of requiring regular maintenance to ensure long engine life and maximum fun out on the water. However, inboard engines are enclosed within the hull of the vessel, as opposed to outboard motors that are mounted outside the hull, and require some different maintenance steps. This article walks you through the critical steps of Mercury Mercruiser inboard maintenance.

Mercury MerCruiser Alpha One Water Pump Impeller Repair Kit.jpg

Mercury Mercruiser Inboard Engine Components to Monitor & Maintain

Water Pump Impeller

Over time, the rubber impellers may dry, rust, and crack. A damaged water pump impeller can cause the engine to overheat and can cause very significant engine damage making it a problem that needs to be repaired immediately.

Most Popular Water Pump Repair Kits:

Mercury MerCruiser Alpha One Water Pump Impeller Repair Kit 817275Q05

Mercury MerCruiser Inboard & Bravo Sea Water Pump Impeller Kit

Fuel-Water Separating Filter

Fuel-water separating filters are important to remove debris from your fuel that can clog and damage your engine. Additionally, these filters are designed to remove excess water from your fuel. PartsVu offers the filters as well as a fuel-water separating filter kit that includes the filter wrench.

Featured Products:

Mercury Quicksilver Water Separating Fuel Filter

Mercury Quicksilver Water Separating Fuel Filter with Filter Wrench

Mercury Mercruiser Water Separating Fuel Filter Kits

Propeller Shaft

The prop shaft should turn without any resistance. If the propeller shaft is turning stiffly, there could be problems with the shaft, engine mounts, strut, or engine alignment.


Mercury Bravo 3 Aluminum Anode Kit

Whenever you have two different metals immersed in salt water, some amount of current flows between the two metals. The electrons that make up this current are supplied by one of the metals giving up bits of itself--in the form of metal ions--to the seawater. This is called galvanic corrosion and, left unchecked, it quickly destroys underwater metals. Anodes must be periodically replaced to prevent this damage.

Featured Product:

Mercury MerCruiser Bravo 3 Aluminum Anode Kit

Manifolds and Exhaust Riser

Check your inboard engine's exhaust risers and manifolds for leaks as leaking exhaust risers can allow water to enter the engine. Rust stains and corrosion on the exhaust risers and exhaust manifolds are also evidence of leaks. While the risers and manifolds permit a small amount of leakage due to their metal parts expanding and shrinking when they heat and cool, excessive leaks need to be investigated and exhaust risers and manifolds will need to be replaced periodically.

Engine Hoses

Hoses must be replaced right away when they start to crack as cracks lead to leaks and can cause severe engine damage.

Propeller Shaft Stuffing Box

Inspect the propeller shaft stuffing box for signs of leakage due to improper adjustment or wear and tear. Check the stuffing box while the boat is docked but still on the water.

Universal Joints, Shift cables, and Exhaust Bellows

Check the universal joint, shift cable and exhaust bellows on your outboard engine and replace as needed as u-joints and the rubber bellows that protect them are subject to wear and tear. Additionally, rubber bellows can also be damaged by debris in the water and animals. If damaged rubber bellows are not replaced, your boat can take on water and eventually sink.

Recommended Products:

Mercury Quicksilver Bellows Adhesive

Mercury Quicksilver MerCruiser Brave 1, 2, 3, Outdrive to Bell Housing Install Gasket Kit

Gimbal Bearings

Usually, a boat owner will suspect a gimbal bearing problem only after they have heard a "growling" noise from the transom or drive area. The growl will be more pronounced when the steering wheel is fully turned to one side or the other. Once this noise is heard immediate action must be taken to prevent further damage. Gimbal bearings usually don't just fail on their own. Water in the u-joint bellows or lack of lubrication are the two main causes of failure. Regular inspection and lubrication with Mercury Quicksilver 2-4-C 8oz Marine Grease Lubricant are great ways to prevent this failure and possible engine damage.

Featured Products:

Mercury MerCruiser Bravo & Alpha Transom Assembly Gimbal Bearing Kit

Mercury Quicksilver 2-4-C 8 oz Marine Grease Lubricant

Mercury Grease Gun

Mercury High-Performance Extreme Grease

*Stock Up and Save* - Mercury Quicksilver 2-4-C 3 oz Grease Gun Cartridges Multipack

Engine Oil - Mercury Precision Lubricants

FC W 25 W 40 Mercury Engine Oil.jpg

Boating is not often thought of as a harsh environment, but in fact, it is one of the most demanding environments in which an engine can operate. Marine engines can and are often used for extended periods at wide-open throttle (up to 6400 rpm on some models), in harsh saltwater, and intense UV sunlight. Then, marine engines sit in storage over the off-season, in many cases without any use. Focusing on these demands, all Mercury Marine Precision Oils and Lubricants are specially engineered for the unique needs of marine engines and rigorously tested to meet our high standards, protecting your outboard and providing many years of engine life.

Featured Products:

FC-W 4-Stroke (25W-40) Oil

Synthetic Blend 4-Stroke (25W-40) Outboard Oil

4-Stroke (10W-30) Outboard Oil

High Performance Gear Lube

Mercury High-Performance Gear Lube is engineered to provide maximum protection for sterndrive and outboard lower units. Exclusive formula is engineered to provide extended gear life in extreme conditions including high-speed and high-horsepower applications. Extensively tested to provide excellent protection against corrosion and excessive wear. Specifically formulated to help prevent failures due to water entering the gear housing. Extreme pressure synthetic additives protect gears from metal to metal contact. Since no industry-wide standards exist concerning marine gear oils, it is essential to use products such as Mercury High-Performance Gear Lube which has been specifically designed and tested for marine applications.

Featured Product:

Mercury MerCruiser Bravo Drive High Performance Gear Lube Kit

The Good Old-Fashioned Smell Test

Open the engine compartment and check for smells that can indicate that there is a leak somewhere. If you smell fuel, there is a leak in the engine which is likely around fuel lines, fuel filters, carburetors, and fuel tank fittings. If you smell fuel immediately contact a qualified marine repair shop to inspect your engine. Also, simple and regular fuel maintenance will add years to your engine's life and will improve your engine's performance.

Mercury MerCruiser Bravo Drive High Performance Gear Lube Oil Kit.jpg

Featured Products:

Mercury Precision Care Quickare

Mercury Precision Care Quickleen

Mercury Precision Care Quickstor

Want to learn more about Mercury's 3-step fuel treatment system? Click here to watch video, These simple and regular checks will keep your inboard engine in great shape for years to come.

As always, PartsVu recommends utilizing your local boat dealer if you need assistance. As always, make sure you have the right Mercruiser parts before doing anything. For other kits, like our Mercury Oil change kits, keep shopping with PartsVu. For full maintenance, check out our Mercury Outboard Maintenance Kits to keep your boat running smoothly.



thank you for the comment. I am happy to assist. I ran your serial number 0M336761. This shows the manufacturing date of 01/10/2002. Please let me know if we can further assist.


DRV: 0M407578 5121300LS MERCRUISER ALPHA 1.62:1

Mario Alvarez,

Will not accept returns. Say electronic parts were taken out. The only electronic part is a kill switch that I did not take out of the plastic. Please have a tactical visor to advise your warehouse man in Naples. This is not electronic throttle. It was supposed to be a dual action throttle and shift cable.

James McDonald,

Hello Per,

Based on the serial number you provided, this is the information I was able to obtain:

DRV: 0M407578 5121300LS MERCRUISER ALPHA 1.62:1
Manufacture Date: 01/10/2002
Comments: 4.3L ALPHA MPI DRAIN


Mario Alvarez,

I have a mercruiser V6 220hk 4.3l.
Serialnummer M336761. What year? I have no paper on the engine.

Best regards Per from sweden


I have a merc 5.7 w/a bravo3 out drive. On the top of the engine is a housing for3 fuses 20 amp mini. The middle fuse is always blowing. And it turns off all my gages and the fuel pump. Any suggestions on what to replace. Very frustrating.

Tomas Pino,

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