In the Know

Cat Marine Tips & Advice Part I

The Cat Marine Resource Center is a great resource for helping you maintain your Cat marine equipment. Caterpillar Marine Manager, David O. Ahrens has answered ten common questions. In this two part Q and A series, David will provide you with preventive maintenance tips ranging from reducing white smoke at start-up to preventing galvanic and stray current corrosion.

Q: When should I use antifreeze?

A: Antifreeze is used to protect the engine coolant from freezing. In areas of the world where the temperature drops below 32 degrees F (0 degrees C), at least a 50 percent glycol concentration (antifreeze) is needed to avoid cracked blocks.

Antifreeze also raises the boiling point of water. As such, a minimum of 30 percent glycol concentration is recommended in warm climates for protection against engine overheating.

All modern diesel engines also require rust inhibitors. Otherwise, the cooling system will rust and lose efficiency and the engine will overheat. In addition, minute holes can form on the cooling water side of the cylinder liner, which will eventually cause water to leak into the combustion chamber and ultimately destroy the engine.

Some brands of antifreeze contain rust inhibitors, although rust inhibitors can also be purchased separately. Be aware that as antifreeze ages, it may still protect coolant from freezing or boiling but the rust inhibitor chemicals may deteriorate. A simple litmus paper test is available to check the proper strength of the rust inhibitors. As a rule of thumb, check your cooling system fluids after every 250 hours of operation.

Q: How should I care for my boat’s battery? 

A: Batteries are required to do more and more on modern boats, including starting engines and powering radios, radar, lights, pumps and other electronics. Batteries have a finite life, which depends in part on the quality built in by the manufacturer. Regardless of the type of battery in your boat, there are some basic steps you can take to keep it working properly.

  • Make sure the battery is securely mounted. Batteries must be securely held in the battery box. Shock and vibration can seriously decrease battery life and lead to premature failure. Hold-downs should also be tight and free of corrosion.
  • Clean battery surfaces. Keep the top surface of the battery clean, as dirt can conduct electricity and silently rob your battery of stored energy. The electrical connections must be kept clean and corrosion-free. Use grease or a cleaning spray to prevent algae growth.
  • Check battery cable connections weekly. Make sure all connections are tight and free of corrosion. When accessories are added to a boat, additional wires should never be connected directly to the battery. Connections must be made to the power panel, through fuses or circuit breakers properly sized for the type of wire used to carry power.
  • Visually inspect all cables. Battery cables must be kept clean and properly supported along their run to the power panel. Look for cracks, breaks, tears or other damage to the cables. Check end connections for gaps between the connectors and coating. If you notice corrosion on the wires in the cable, replace the cable. Clean the posts regularly and coat with a corrosion retarder.
  • Inspect all starter connections. Regularly check the connections between the battery and starter switch, and between the starter switch and the starter itself. Check the starter mounting bolts for tightness. Lubricate starter bushings and/or bearings when necessary.
  • Check charging circuit connections. Inspect all connections between the battery, regulator and alternator. Make sure connections are tight and corrosion-free. Inspect the wiring for cracks, worn spots or general deterioration.
  • Check electrolyte levels and state of charge. If your battery has cell caps that can be opened, check the level of the electrolyte in each cell monthly. If the level is low, add distilled water. Some batteries (such as “maintenance free” types) are built with sealed cell covers and sufficient fluid to last the lifetime of the battery. The only way to check the condition of these sealed batteries is with a load test, carried out with a specialized piece of test equipment.
  • Track discharging levels. If you are using the battery to run things when the engine or generator is not operating, don’t discharge the battery below 12.2 volts. Never discharge a battery below 11.8 volts. Use a digital voltmeter to check battery voltage. Recharge the battery promptly after using it, as leaving it in a semi-discharged state will shorten its life.

Battery fluid is diluted sulfuric acid, so remember to always use caution when working with batteries. Wear protective goggles and try not to splash acid on clothing, the top of the battery or nearby surfaces. If any acid is spilled, replace the battery cell covers and wash the top of the battery with plenty of fresh water. Periodically clean the top, using a mixture of water and bicarbonate of soda to neutralize any acid residue. Dry the battery top after cleaning it.

With proper care, most moderate quality batteries used on commercial boats can be expected to last at least three years, while premium quality batteries can last for more than seven years. There are no bargain batteries. Finally, make a note of the date on which your battery was installed and post it near the battery where it can be seen each time you check the battery. Time flies and what you may think of as a relatively new battery may be years older than you thought. 

Q: How should I care for my engine’s cooling system?

A: The first step for cooling system care is making sure you’re using the proper fluids. Either distilled or deionized water should be used with an approved antifreeze and an approved supplemental coolant additive or rust inhibitor. (Fishermen in warmer climates don’t need to use antifreeze but must still use the coolant conditioners.) Use a low-silicate antifreeze that meets one of the following specifications: GM 6038-M or ASTM #D4985. The fluid in the jacket water cooling system should not consist of plain tap water or water which has been “softened” by a domestic water softener. Tap water is not recommended for engine cooling systems because of additives, contaminants and other chemicals (such as salt, chlorides, sulfates, etc.) found in the water.

Corrosion of the water-cooled side of cylinder liners can occur when 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 base antifreeze containing approved corrosion inhibitors or distilled water, plus an approved cooling system conditioner.

Here are some additional tips to incorporate into your regular maintenance schedule to keep your cooling system in good shape:

  • Replace hoses approximately every three years of engine operation
  • Replace the fluid in the cooling system or replenish the inhibitor chemicals at intervals listed in your owner’s manual. Although the glycol in the antifreeze mixture does not wear out, the corrosion inhibitors lose their effectiveness over time. You can eliminate the need for multiple additive replacements by using the new Cat® _Extended Life Coolant, which requires only one addition of “extender” at 3,000 hours or three years
  • Consider a coolant analysis program, such as the SOS coolant analysis offered by Caterpillar Inc., to evaluate the effectiveness of your coolant and check for contaminants
  • Clean the water pump drain vent and inspect for leakage of the pump seal
  • Inspect and maintain the sea water coolant system. Clean the sea water strainer, check the pump impeller at least annually (or monthly for rubber impeller pumps) and periodically clean the heat exchangers
  • Periodically inspect and replace zinc anodes used in the seawater system
  • Check coolant level before starting the engine
  • Ensure that the engine room ventilation system is adequate

In addition, the filler cap on pressurized cooling systems includes a valve that permits the system to operate at above atmospheric pressure. Pressurizing the jacket cooling system increases the boiling point of the coolant, increasing the efficiency of the cooling system. Fluid level in this type of system is normally checked when the engine is cool.

Proper engine cooling system operation is best achieved by always performing all required inspections and checks. It may take some extra work, but it’s better than having to deal with an overheated engine. 

Q:  What can I do to prevent galvanic and stray current corrosion?

A: Corrosion due to electrical activity can be very destructive and costly. Let’s review the basics so that this silent destroyer doesn’t hurt you!

Galvanic Corrosion

All hulls which operate in water will be subject to some galvanic corrosion. Place two different metals in sea water, connect them with a wire and current will flow from one to another. The bad news is when the current flows, metal particles from the basic metal will deposit themselves on the noble (more corrosion resistant) metal. Eventually the basic metal will corrode away.

The following items can minimize the problems caused by galvanic corrosion:

  • Use similar metals wherever possible
  • Make the smaller, more expensive parts (such as propellers, rudders and seacocks) from a more noble metal (graphite, platinum, titanium, stainless steel and copper nickel compounds) than the larger, less expensive items
  • Insulate dissimar metals with a gasket or flexible compound to avoic contact (or “electrical conductivity”) between them
  • Bond similar metals to a “common” ground
  • Avoid the use of graphite grease. Instead, use a lithium or moly based grease, which are advertised as being “non-conductive.”
  • Provide sacrificial anodes! Since it’s almost impossible to prevent all galvanic action, a sacrificial anode made of zinc is the most common solution. The zinc is placed in strategic locations where it can be monitored. It’s relatively cheap to replace the zinc as it deposits itself on the larger surfaces.

Your engine manufacturer installs zinc rods in the engine’s sea water cooling system. When the new engine goes into service, the zincs should be inspected hourly. As the zinc rods corrode away, a white crust of oxides and salts form on the surface, which will flake off when tapped. Later, as you gain experience, the inspections can be lengthened to daily or weekly until you determine the proper service interval. If the zinc remains clean and like new, it’s not protecting like it should.

Stray Current Corrosion

Galvanic activity usually progresses slowly, sometimes taking months or years before serious corrosion is apparent. The voltage difference between the two metals may be only millivolts (1/1000ths of a volt). Stray currents, on the other hand, can be thousands of times greater and can destroy expensive components in hours.

Here are some things that may cause problems:

  • Poor insulation, especially in damp areas of the boat
  • Undersized wiring, which causes excessive voltage drops. The electricity then tries to find a better flow path
  • Cheap appliances which leak electricity
  • Radio grounds with different voltages than the battery ground
  • Lack of a common ground point
  • Tying the AC systems neutral to the boat’s ground system without an isolation transformer
  • Defective shore power wiring can cause problems between two boats electrically tied together at a marina

To prevent stray current corrosion, the following practices are recommended:

  • Wire the boat like your house, not your car. Modern homes have three wires to every outlet. One from the electricity source, a return line to the electricity source and a ground wire. (Your car has only one wire that goes from the battery to the appliance. The car’s chassis is used as the return line. There is no path to ground because of the rubber tires.)
  • Use two wire marine appliances, not single wire automotive appliances (e.g., engine alternators and starters, bilge pumps, etc.). Make sure both the electrical supply wire and the return wire are large enough. Devices that work well on land may be unsuitable in a marine environment.
  • Use a common ground for all systems. Use a keel bolt to an external ground plate, not the engine block
  • 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 not in use
  • Check your boat with a Voltmeter. Look for voltage readings where there should be none.

Finally, if you don’t have a lot of marine experience, call a pro. Some corrosion problems can be quite subtle and hard to figure out. It pays to hire an expert. It’s much cheaper than replacing expensive components.

Q: What’s involved with scheduled oil sampling? 

A: There are two ways to take a Scheduled Oil Sample (S.O.S.) - by using an oil valve probe or by vacuum extraction when the engine is at normal operating temperature. After it’s taken, the sample is placed in a carefully labeled bottle and sent to the dealer’s S.O.S. lab. There it is checked for water, glycol, fuel and trace elements, such as sodium, silicon, chromium, aluminum and iron. If the sample indicates potentially troublesome elements or fluids, your dealer will contact you to discuss corrective measures. Take oil samples regularly, so that a change in magnitude of one or more of the elements can be observed, the correct diagnosis made and remedial measures taken. The goal is to identify potential problems early and avoid major engine failures.

Q: How often should I change my oil and oil filter?

A: That depends on your engine and how you use it. The Operation and Maintenance Manual for your engine will usually include a “standard” oil change interval based on fuel used or hours of operation. This interval may be lengthened if your engine has a larger-than-standard oil capacity or shortened if your engine is operated under conditions that tend to cause oil degradation. Factors that may shorten the interval include operating with a high load factor (80 to 100 percent), operating with jacket water temperature under 175° F, when humidity is over 85 percent or when using improper fuel or poor maintenance techniques. Fuel consumption is an indication of load factor. The engine manufacturer may recommend oil changes after a given number of gallons of fuel used, especially for applications with high load factors. Any time that oil change/maintenance intervals are extended, samples should be taken to verify that the extended intervals are justified. 

Get more Cat Marine tips and advice in Part II

San Diego - Marine Engine
Dan Hixon

General Service Manager

858.376.6822 office

858.663.4652 mobile

San Diego - Parts

Bob Hutter 

General Parts Manager

858.674.7100 office

Hawaii - Marine Engine

Doug Kaauwai
Heavy & Hydraulic Service Manager
808.676.0306 office
808.265.1863 mobile

Hawaii - Parts

Lisa Kong

Corporate General Parts Manager

808.676.0256 office

808.368.5477 mobile