Eight Marine Engine Maintenance Tips

Get eight preventive maintenance tips from Cat marine engine experts. Let us help you keep your vessel’s engine running at peak performance.


1. Boat’s Battery

Batteries start engines and power radios, radar, lights, pumps and other electronics on the boat. To make sure your battery works properly, there are some basic steps you should follow.

  • Battery. Make sure it’s properly secured in the battery box, otherwise, in case of shock and vibration, the battery’s life can be decreased and lead to premature failure.
  • Battery surfaces. The battery’s hold-downs should be tight and free of corrosion. The battery’s top surface needs to be clean. Electrical connections must be kept corrosion-free and clean. To prevent algae growth, you can use cleaning spray.
  • Battery cable connections. Weekly checkups will help you to make sure all connections are tight and corrosion-free.
  • Cables. Check for cracks, breaks, and tears. Battery cables need to be kept clean and properly supported along their run; corroded wires need to be replaced. Clean the posts on a regular basis and coat with a corrosion retarder.
  • Starter connections. Connections between the battery and starter switch, as well as connections between the starter switch and the starter, need to be checked regularly. Check the tightness of the starter mounting bolts. When necessary, lubricate starter bushings and/or bearings.
  • Charging circuit connections. All connections between the battery, alternator, and regulator need to be inspected. Connections should be tight and corrosion-free, wiring should be checked for cracks, work spots, or general deterioration.
  • Electrolyte levels and state of charge. Batteries that have cell caps that can be opened should be checked monthly to identify the level of the electrolyte in each cell. When the electrolyte level is low, add distilled water. “Maintenance-free” types of batteries are built with sealed cell covers and contain sufficient fluid to last the lifetime of the battery. The only way to check the condition of these types of batteries is with a load test by using a specialized piece of testing equipment.
  • Track discharging levels. If the battery is used to run when the engine or generator is not operating, don’t discharge the battery below 12.2 volts. The battery should never be discharged below 11.8 volts. You can check battery voltage using a digital voltmeter. After using the battery recharge it promptly, leaving is in a semi-discharged stage will shorten its life.


2. Engine’s Cooling System

The first step in cooling system care is to make sure you are using the proper fluids. Distilled or deionized water should be used with an approved supplement coolant additive or rust inhibitor. Check low-silicate antifreeze specifications, it should meet one of the following requirements: GM6038-M or ASTM #D4985. The fluid in the jacket water cooling system should not consist of plain tap water or water that has been softened by a domestic water softener. It’s not recommended to use tap water for engine cooling system: it contains additives, contaminants, and other chemicals such as salt, chlorides, or sulfates.

Corrosion of the water-cooled side of cylinder liners can occur if supplemental cooling system conditioners are not used or are depleted. Jacket water systems should always be filled with a Caterpillar-approved coolant mixture, a 50-50 mixture of distilled water, and an approved glycol-based antifreeze that contains approved corrosion inhibitors or distilled water and an approved cooling system conditioner.

Here is the additional list of tips to include into your regular maintenance routine to keep your cooling system in good shape

  • Hoses need to be replaced approximately once every three years of engine operation.
  • When the fluid in the cooling system needs to be replaced, the inhibitor chemicals need to be replenished. Recommended intervals are listed in your owner’s manual.
  • Consider a coolant analysis program to evaluate the effectiveness of your coolant and also check for contaminants. Caterpillar offers S•O•S coolant analysis.
  • Clean the water pump drain vent and inspect the pump seal for leakage.
  • Inspect and maintain the seawater coolant system: clean the seawater strainer and check the pump impeller at least once a year. Also periodically clean the heat exchangers.
  • Inspect and replace zinc anodes in the seawater system. This procedure is recommended to be done periodically.
  • Check coolant level before starting the engine.
  • Check that the engine room ventilation system is adequate.


3. Prevention Galvanic and Stray Current Corrosion

To minimize the problems caused by galvanic corrosion, follow these recommendations:

  • Use similar metals wherever possible.
  • The following metals are recommended for smaller, more expensive parts, such as propellers, rudders, and seacocks: graphite, platinum, titanium, stainless steel, and copper nickel compounds.
  • Insulate dissimilar metals with a gasket or flexible compound to avoid contact between them.
  • Bond similar metals to a common ground.
  • Avoid using graphite grease; instead use non-conductive grease: lithium or moly based.
  • Provide sacrificial anodes. The most common solution for galvanic corrosion prevention is a sacrificial anode made of zinc.

Galvanic activity usually progresses slowly, unlike stray currents, which can destroy expensive components in hours.

To prevent stray current corrosions, you can follow these practices:

  • It’s recommended to have three wires to every outlet on the boat: one from the electricity source, a return line to the electricity source, and a ground wire.
  • Use two-wire marine appliances. Make sure both the electrical supply wire and the return wire are large enough. Not all the devices that work well on land may be suitable for a marine environment.
  • Use a common ground for all systems.
  • Use a Type-B isolation transformer to tie the neutral side of the AC system to the boat’s common ground.
  • Install an isolation switch to disconnect your battery when it’s not used.
  • Check your boat with a voltmeter. Look for voltage readings where there should be none.


4. Pitting in Cylinder Liners

Pitting in cylinder liners is directly related to cavitation erosion, which develops from normal mechanical and chemical processes that happen when an engine operates.

The best way to prevent cavitation is to follow your engine manufacturer’s recommendations on additive replacement. When a standard heavy duty coolant is used, SCA (Supplemental Coolant Additive) should be added every 250 hours—it will help to replenish the eroding oxide film.


5. Simplified Preventive Maintenance

Preventive maintenance includes three categories: preventive maintenance items, revolution-sensitive items, and load-sensitive items.

Preventive maintenance items should be performed at the hours that are indicated on the schedule. Otherwise, engine life and performance will be affected.

The maintenance intervals for revolution-sensitive items are usually based on hours of operation. If an engine runs faster and longer, these components will wear out faster. Revolution-sensitive items include: water pumps, alternators, fuel transfer pumps, and oil pumps.

Load-sensitive items are affected by engine load. The best indicator for determining service intervals for load-sensitive items is to look at the total fuel consumed. Generally, the lower the load, the longer the engine life. Load-sensitive items include: cylinder liners and heads, connecting rods, pistons and piston rings, main and connecting rod bearings, and valve train components.


6. Replacing an Engine’s Thermostat

An engine thermostat regulates jacket water temperature. It keeps the engine running at a normal operating temperature, which is usually around 185 degrees F.

To get the most out of your engine, make sure you change your thermostats annually as a part of your routine maintenance. If thermostats are running below 185 degrees Fahrenheit, it’s time to change your thermostats. Advantages of regular thermostat updated include increased fuel efficiency, longer life between overhauls, and as a result, increased engine performance.


7. Adjusting the Valves on a New Engine

Engine valve lash should be adjusted at the first oil change on a new engine. On all Cat marine engines, the first oil change is typically recommended at 250, 500, and 1000 hours.

A valve lash adjustment is critical due to the key role valves of a diesel engine play in the combustion process. The intake valves control the flow of air entering the cylinder, and the exhaust valve controls the flow of exhaust gases exiting the cylinder. Inlet and exhaust valves must close and seal completely during the combustion process.


8. Scheduled Oil, Coolant, and Fuel Sampling

There are two ways to take a Scheduled Oil Sample (S•O•S): by using an oil valve probe or by using a vacuum extraction pump when the engine is at normal operating temperature. Usually, oil is checked for water, glycol, fuel, and trace elements such as sodium, silicon, chromium, aluminum, and iron. Take oil samples regularly, so that a change in elements can be observed and remedial measures could be taken. The goal is to identify potential problems earlier and prevent major engine failures.