Caterpillar Marine Manager, David O. Ahrens of the Cat Marine Resource Center has answered ten common questions. In part two of 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: What causes pitting in cylinder liners?
A: Pitting in cylinder liners is a direct result of cavitation erosion. This type of erosion develops from normal mechanical and chemical processes that take place during engine operation.
Cavitation of the cylinder wall begins when air bubbles remove the wall’s oxide film, which protects the metal from coming into contact with oxygen and corroding. Flexing of the cylinder wall (after fuel combustion) causes the cylinder liner to vibrate, and creates vapor bubbles in the coolant. These vapor bubbles form on the outside of the cylinder wall and explode inward, or implode, resulting in tiny pits on the cylinder wall’s protective oxide layer. When vapor bubbles continue to implode, enough energy is released to physically attack the cylinder wall and remove the oxide film. Corrosion and pitting then take place at a high rate.
If a pit breaks through the cylinder wall, coolant can leak into the cylinder and contaminate the lube oil. A sludge forms that can interfere in ring and bearing functions. Wear rates increase significantly and engine seizure may result.
The best way to prevent cavitation from occurring is to follow your engine manufacturer’s recommendations on additive replacement. When using a standard heavy duty coolant, SCA (Supplemental Coolant Additive) should be added every 250 hours to help replenish the eroding oxide film. Caterpillar has recently introduced an Extended Life Coolant (ELC), which provides a substantial amount of protection and lasts longer than standard heavy duty coolants. ELC eliminates the need for multiple additive replacements – requiring only one addition of extender at 3,000 hours.
If you modify your cooling system, remember to keep the pressure cap furnished with the expansion tank. Removing this cap allows a lower operating pressure inside the engine. That will cause more vapor bubbles to form, resulting in cavitation.
Q: I understand the value of preventive maintenance, but is there any way to simplify when engine maintenance should be performed?
A: Items in your maintenance schedule fall into one of three categories...preventive maintenance items, revolution-sensitive items and load-sensitive items. Preventive maintenance items should be performed at the hours indicated on the schedule. If not, engine life and performance will be adversely affected. The maintenance intervals for revolution-sensitive items are based on hours of operation. The faster and longer the engine runs, the faster the components wear. The load on the engine during operation does not affect these items. Obviously, load-sensitive items are affected by engine load. The best indicator for determining service intervals for load-sensitive items is total fuel consumed, which will vary as the load on the engine varies. In general, the lower the load, the longer the engine life. If revolution-sensitive components are serviced at the proper interval, the risk of a failure is minimized for most users. If you decide to exceed the indicated intervals in the schedules, you assume a higher risk of component failure and unnecessary expense.
As mentioned, the wear rate of load-sensitive items is a function of fuel consumed. An engine operating at 100 percent load takes less time to consume the same amount of fuel as an engine operating at 50 percent load. It follows that it takes less time for an engine operating at 100 percent load to wear the same amount as an engine operating at 50 percent load. Of course, engine load will fluctuate, making it difficult to determine the exact hour interval for servicing. It's therefore important to keep accurate fuel consumption records to properly maintain load-sensitive items.
Here's a list of items that require regular preventive maintenance:
- Water pumps
- Fuel transfer pumps
- Oil pumps
- Cylinder liners
- Cylinder heads
- Connecting rods
- Piston rings
- Main and connecting rod bearings
- Valve train components
Q: What are some of the things I should look for in my engine that signal the need for attention?
A: Ten good reasons to get help for your engine:
- Black smoke under load - dirty air cleaner, turbocharger problems, overload, overfueling
- White smoke - leaking head gasket, cracked head, block or line, bad injector(s)
- Unusual noise - bearings, wrist pins, turbocharger or injectors
- Lack of power - dirty air cleaner, dirty fuel filter, governor out of adjustment, injectors malfunctioning, bad fuel
- High oil consumption - worn rings or liners, worn valve guides, worn bearings, worn turbocharger seals
- Increased fuel consumption - leak in fuel system, dirty air cleaners, poor operation
- Increased oil level - coolant leak
- Overheating - cooling system problems, worn belts, plugged hoses, low coolant level, damaged or malfunctioning temperature regulator
- Hard starting - worn injector pump, low cranking speed, poor quality fuel, plugged fuel line or filter
- Trash in the oil filter - excessive bearing wear, damaged internal parts, coolant or fuel leaks into the crankcase, extended oil drain interval, improper oil, additives
Q: What is the difference between an engine part rebuilt in a local shop and a part remanufactured by an engine manufacturer?
A: When a part is repaired or rebuilt by a local repair shop, it means the part is restored by refinishing worn surfaces and installing new components such as seals or bearings. A remanufactured part, however, is a part returned to the original engine manufacturer. In the case of Caterpillar, the part is cleaned and disassembled. All worn parts are replaced with new, genuine Cat parts. The part is then tested to make sure it meets original specification requirements.
When comparing a remanufactured part with a locally rebuilt part, ask yourself these questions:
Will the part contain all the necessary technical improvements incorporated since the engine’s original production? One can be assured that a remanufactured part will contain any critical improvements and meet the latest factory specifications.
What kind of warranty will I get? Caterpillar offers the same warranty for a remanufactured part as it does for a new part. Local rebuilders may only offer a limited, locally-honored warranty.
Q: How quickly do I need the part? Time is money. Turnaround from a rebuilder may not be as fast as purchasing a new or remanufactured part from the factory.
A: How extensively will the part be tested? Caterpillar tests every remanufactured part to ensure it meets performance specifications. All worn components are replaced with new ones, and the result is a part that is as good as new. Rebuilders may have testing capabilities, but results vary based on the equipment used and the person conducting the test.
What about cost? Remanufactured parts offer excellent value. Reuse of the basic structure, together with efficient production machinery and processes, make it possible for Cat remanufactured parts to be sold at a price 20 to 60 percent less than the cost of a new production part.
Q: Does Caterpillar recommend using fuel additives?
A: There are many aftermarket additives available for neutralizing undesirable fuel properties or improving ignition quality. But, the performance of these additives vary. The fuel in your tank may have already been treated with additives when it was transported through the pipelines, and additional additives may not be compatible with the fuel. As such, Caterpillar generally discourages the use of fuel additives for No. 1 and No. 2 diesel fuel, with two exceptions: First, if the fuel’s cetane number is below 40, use a cetane improver for direct injection engines. Second, if microorganisms are present in the fuel, use a biocide to eliminate them.
Recently, low fuel lubricity (the lubricating quality of fuel) has been associated with low sulfur fuel. The process used to remove sulfur from fuel – called hydro-treatment – also eliminates certain materials and compounds which are known to improve the lubricity of fuel. The engine fuel system is less tolerant of water and dirt contamination with fuel that’s low in lubricity. Fuel not meeting the minimum lubricity specifications requires additives. However, you should be cautious about using fuel lubricity additives, as some can form deposits in the fuel injection system. If low lubricity is an issue, consult your fuel supplier for proper recommendations regarding fuel lubricity additives.
Q: What is Caterpillar doing to its marine engines to help reduce white smoke at start-up?
A: White smoke, which is basically unburned fuel, is often noticed at engine start-up for several reasons. First, fuel is not burned efficiently when the engine runs at idle or at low engine speed without load, which are normal start-up conditions. Cold ambient air temperatures and cold engine coolant temperatures also contribute to inefficient combustion. Another major factor is retarded timing, which means the fuel is injected after the optimum time for complete combustion. (Retarded timing is used to help improve starting capabilities, decrease noise or lower engine emissions.)
Caterpillar has made several improvements to its engines to reduce white smoke at start-up. Various attachments are available to shorten the time it takes for the engine to reach operating temperature by heating the coolant or the inlet air. These include jacket water or block heaters, and inlet air heaters. Attachments vary among different engine models.
Caterpillar has also made iron modifications to help reduce white smoke. Using different pistons to increase the compression ratio or altering the opening and closing of valves can reduce white smoke, too. For example, the 3208 marine engine rated 435 bhp (326 bkW) has a camshaft that closes the inlet valves earlier. This makes start-up more efficient, reducing smoke.
White smoke is typically not as much of a problem with electronically governed engines as it is with mechanically governed engines. This is because fuel injection timing is controlled by software rather than mechanical devices. All Cat electronic engines feature a Cold Start Strategy that is activated when the coolant temperature falls below a certain point. This strategy can advance the fuel injection timing even when the rpm is low, or make the engine run on a portion of the cylinders until the engine is warm. For example, the 3406E marine engine uses only three of the six cylinders during cold mode operation.
Finally, refer to your engine’s operating and maintenance manual for the recommended fuel and lube oil for the ambient conditions in which the vessel operates.
Q: I’m storing my boat for a few months over the winter. What diesel engine maintenance procedures do you recommend?
A: If your engine will be stored less than six months, protect your investment by following these short-term storage procedures:
- Change the oil. Drain the oil out of the sump, replace it with the appropriate diesel engine oil and change the filters. Start your engine and operate it long enough to pump fresh oil throughout the engine, approximately five to ten minutes. Using the right type of oil and changing the oil and filter at the proper intervals helps prevent sticking piston rings, piston seizure, accelerated wear of the in-cylinder components and bearings. Refer to the owner’s manual for the correct procedure, viscosity and amount.
- Drain water and sediment from your fuel filter/water separator – and from the fuel tanks, if possible. Replace the filter. Consider using a biocide in the main fuel tanks to prevent the growth of bacteria. Follow the biocide manufacturer’s instructions carefully. Too much biocide can harm the fuel system.
- Drain water and sediment from the bottom of the fuel injection pump housing, if applicable.
- Remove and replace the secondary fuel filter on the engine. Replace it with a manufacturer-recommended fuel filter.
- Top off the fuel tanks with clean, fresh diesel fuel. Use the priming pump to completely fill the primary fuel filter/water separator, secondary fuel filter and fuel injection pump housing with clean, treated diesel fuel.
- Check the freeze protection of the coolant mixture. Make sure the freezing point of the coolant is lower than the expected low temperature your engine will experience during storage. Verify that the coolant conditioner percentage is between 3 and 6 percent. Drain and flush the cooling system every two years when using a low silicate antifreeze. If you use Cat Extended Life Coolant (ELC) and a mid-life extender, drain and flush the system every six years. Change the water temperature thermostat when flushing the system or if the engine has been operating below 180oF.
- Drain the engine’s sea water system. Remove and inspect the zinc rods in the cooling system and replace them, if necessary. Flush the sea water system with clean, fresh water and allow the water to drain from all compartments. If your boat uses a water lift muffler, flush the sea water system only when the engine is running, otherwise, water could enter the engine and cause severe damage.
- Inspect the sea water pump impeller. Replace the pump cover gasket and impeller if it shows signs of damage or excessive wear. At this time, also inspect the sea water pump drive belt for damage or wear. Replace the belt if necessary.
- Inspect and replace all rubber hoses as necessary. Replace all rubber hoses every two years. This can be performed during the cooling system flushing procedure (i.e. hoses from through-hull fitting to sea strainer, sea strainer to sea water pump inlet, marine gear outlet to the wet exhaust discharge fitting and any other cooling system hoses).
- Lubricate all fittings on the engine. Refer to your owner’s manual for the proper procedures.
- Drain the oil from the marine gear and clean the filter/screen according to the manufacturer’s recommendation. Check the gear oil level with the engine running. Fill with the appropriate oil. Do not overfill the gear, but make sure there is sufficient oil for starting.
- Remove batteries from the boat during the storage period. Fill the batteries with distilled water and fully charge them. Clean the battery and cable connections, and apply a light coating of multipurpose grease to prevent battery connections from corroding. Store the batteries in a cool, dry location during the storage period.
- Remove the air cleaner filter element. Clean or replace the filter element as necessary. The crankcase breathers should also be cleaned at this time. If your boat is equipped with a closed-crankcase system, check all hoses and fittings and service per the manufacturer’s recommendations.
- Use an appropriate cleaning solvent to remove all oil and dirt from the engine. Be careful not to allow the solvent or water to enter the intake system through the air cleaner. Allow the engine to dry and touch-up your engine and marine gear with paint as necessary.
Q: Why do I need to replace my engine’s thermostat?
A: An engine’s thermostat (or “temperature regulator”) regulates the jacket water temperature to keep the engine running at a normal operating temperature, usually around 185 degrees F.
If the jacket water becomes too hot, the thermostat “opens” to allow cold water in from either the keel cooler or heat exchanger. When the jacket water returns to a normal operating temperature, the thermostat “closes” to keep the cold water out. An old or deteriorating thermostat, however, may not recognize when to close off the cold water and subsequently overcool the engine. Overcooling can damage an engine as much as overheating because the parts don’t expand properly, and the engine is allowed to run under any load at substandard temperatures.
The biggest problem associated with running too cool is excessive carbon buildup around valve guides and behind piston rings. Other problems include combustion contaminants in the oil and the presence of sulfuric acid, which can attack the rings and
To get the most out of your engine, change your thermostats annually as part of your routine maintenance schedule. You can also determine thermostat wear by monitoring the coolant temperature under load. If it’s running below 185 degrees F, change your thermostats. (Caterpillar engines usually have two or four thermostats per engine. If one fails, change all of them.) The advantages to a regular thermostat changeout is increased fuel efficiency, longer life between overhauls and increased engine performance.
Q: What do you think about the use of synthetic oils in marine applications?
A: Synthetic base stock oils generally outperform non-synthetic oils in two areas: improved oil viscosity in low operating temperatures and improved resistance to oxidation in high operating or ambient temperatures. Oxidation occurs when oil molecules combine with oxygen. Heat from the engine acts as a catalyst for oxidation, causing the oil to thicken, lose its lubrication characteristics and its ability to resist wear and corrosion.
Some synthetic oils have a characteristic that enhances the useful service life of the oil, which can help lengthen oil service intervals. Caterpillar doesn’t recommend automatically extending oil change intervals for any oil, including synthetic base stock oils. Oil change intervals should only be adjusted through an oil analysis program that includes oil condition and wear metals analysis, trend analysis, fuel consumption and oil consumption. The extra benefits found in synthetic oils are reflected in the price -- synthetic oils are typically two to four times more expensive than non-synthetic oils.
Q: When do I need to adjust the valves on my new engine?
A: Engine valve lash should be adjusted at the first oil change on a new engine. On Caterpillar® Marine Engines, the first oil change is typically recommended at 250, 500 or 1000 hours.
A valve lash adjustment is critical because the valves of a diesel engine play a key role in the combustion process. Specifically, the intake valves control the flow of air entering the cylinder, while the exhaust valve controls the flow of exhaust gases exiting the cylinder. Both inlet and exhaust valves must close and seal completely during the combustion process.
Technically, the valve itself is not adjusted, but rather the valve mechanism, i.e., the lifter, push rod and rocker arm assembly. The valve mechanism is adjusted to provide a specific lash (or looseness) necessary to regulate the opening and closing of the valve. If the lash is too loose, the opening and closing of the valve becomes very abrupt which will eventually lead to damage to the valve and/or valve mechanism. If the lash is too tight, the valve cannot close and seal properly in the cylinder head and exhaust gases will leak past the valve. With incorrect lash adjustment, the engine may not operate at full power, fuel consumption may be high and the exhaust smoke and exhaust temperature may be excessive. If left uncorrected for an extended period of time, a catastrophic failure of the valve and engine is likely to occur.
Valve lash adjustment is a relatively uncomplicated procedure. Valve lash should be checked and adjusted as needed as a normal maintenance process every 1,000 to 3,000 hours after the initial adjustment. Consult your Operation and Maintenance Guide for the correct interval and procedure to adjust the valve lash for your engine.
Q: How Does Cat Electric Offer Extended Life for my engine?
A: Read the brochure for more information.
For more tips and advice read Part I.
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