The other engine maintenance


A lot has been written about maintaining a diesel engine. Topics such as fuel systems, cooling systems and changing the oil are all well covered in the maintenance manuals. When it comes to marine diesels, most books and manuals focus on the engine itself and only touch on all the hoses, wires and cables connected to the motor. Fuel tanks, fuel lines, electrical systems and controls all play a part in an engine’s reliability. Even the best-maintained engine can fail if the systems connected to it are not in good working order.

All these systems connected to your engine can, if not properly cared for, cause issues that are sometimes misdiagnosed as problems with the engine itself. Bad fuel lines are often misdiagnosed as clogged fuel filters or failing fuel pumps, poor electrical connections can result in slow starting, and clogged raw-water intakes can appear to be a bad raw-water impeller. This is why it is important to check not only the engine but everything connected to it.

For example, many voyagers stop at replacing fuel filters when doing maintenance on the fuel system. Any fuel system starts at the fuel tank and slowly moves the fuel to the engine through a series of tubes, hoses, valves and pumps. All of these parts are important and all need periodic checking and maintenance. Fuel tanks should be cleaned every few years, removing any water or sediment. Fuel lines and hoses should be checked for condition and age. Rubber fuel can deteriorate from the inside, causing blockages that cannot be seen.

Rust on this exhaust elbow indicates a weeping leak that needs repair.

Valves should be checked for operation and serviced if hard to turn. Make sure all fuel lines and hoses are properly secured and free of damage and chafing. For obvious reasons, make sure no electrical wires are secured to any fuel lines. Check all connections and hose clamps, and change out any suspect fittings. Do not forget to check the tank pick-up tube, as these can become clogged or restricted with time. Finally, make sure the tank vent lines and fitting are clear, as these can be a nice home to insects blocking the vent and create a vacuum in the tank as the motor draws fuel. A good low-resistance fuel flow from the tank to the motor is important to a healthy fuel system.

In order to burn that fuel, an engine will need to take in air for combustion and then let the burned exhaust gases safely out of the boat. Make sure all air intakes are free from obstructions and air filters are clean. Check hull vent openings, blowers and air hoses. Make sure there are no loops in air hoses that could fill with water and block the air flow. Exhaust hoses should be checked for general condition and for signs of leaks. Many rubber exhaust hoses can dry rot and crack like an old tire, which can result in failure.

Any mufflers and waterlocks should be checked for leaks, cracking and corrosion. Make sure all hoses and mufflers are also well secured to the vessel to prevent chafe damage — an exhaust hose can move due to fluctuating pressures in the hose. Check all hose connections, verifying that each connection has a minimum of two hose clamps. Check the condition of the exhaust through-hull fittings as well. These are typically hard to get to inside the boat and are often left uninspected for years. Failure of the through-hull fitting can result in flooding of the vessel.

These dry-rotted cooling hoses should be replaced before they fail.

The exhaust system also plays a part in the engine cooling. Once the raw water used to cool the motor has done its job, it is mixed with the exhaust gases to cool the exhaust before finally being sent overboard. This is another reason why a good exhaust system is important. The mixing elbow on the back of the motor is also an area of potential problems. Hot exhaust gases mixed with hot raw cooling water under high temperatures and pressure are a perfect mix for corrosion. Because of this, exhaust risers and elbows should be checked at least annually. Make sure there are no blockages where the water goes into the riser or elbow; this is common, particularly with cast-iron risers. On the other end of the cooling system is the raw-water intake. Good free-flow of raw cooling water will save frustration with impellers giving up too soon and heat exchangers working without a good flow of water. Part of any cooling system maintenance should start at the through-hull and work toward the engine. Make sure the intake is not clogged with marine growth and any strainers are clean. Check the hoses’ clamps and fitting for corrosion. Pay particular attention to any kinks or sharp bends in the hoses that could restrict water flow.

As a surveyor, I am often shocked at some of the wiring I see connected to engines. Electrical connections require special attention for several reasons. To start, some of these connections are high-amperage, requiring properly sized conductors and good solid connections to work properly. Starter motors may work with undersized conductors or poor connections but will suffer and fail prematurely if they do not get the correct current flow required.

Charging systems, often producing more than 100 amps, likewise will perform poorly if the conductors are undersized or connections are poor, leaving the owner wondering why their batteries are not charging properly. Starting and charging circuits are only part of the equation with many electrical connections for instrumentation and controls. Engine manufacturers will also often use multi-plug connectors for their wiring harnesses. All these connections need to be checked for tight corrosion-free connections. Engines vibrate and move more than almost any other equipment aboard. This vibration can cause connections to loosen, creating resistance and failures. It can also create chafing that can result in shorting or wire damage.

A poorly supported air vent hose.

A routine inspection of all electrical connections and wires connected to and around the motor will help avoid problems. Starting loads are high, and the starter cables should be checked both at the engine end and at the battery post. Battery explosions are often the result of poor connections at the battery causing heat and sparks that can ignite battery gases. Poor connections here can cause overloading of the starter, reducing its life and making the engines harder to start. Check connections on the alternator as well, as these are also high-load connections subject to loosening from vibration. While at it, do not forget to check the ground wires to the engine block. The main ground should be attached as close to the starter as practical. It is not enough to just visually inspect these connections; rather, a wrench should be used to verify the tightness of the fittings.

A quick inspection should also be made of all other wires attached to the motor. Make sure they’re tight and no corrosion is evident. Check that all wires are secured to the motor near the connection to reduce loads on the connections from the weight of the wires and vibration. All wires and harnesses should be routed so as to prevent contact with vibrating, moving or hot parts of the motor. If necessary, add chafe protection to any conductors to prevent damage. Once again, make sure wires are not secured to fuel lines — a conductor heated by a short could burn through a fuel hose with some not-so-pleasant results.

Another important part of any motor installation is the controls that actuate the throttle, shift, and in some installations the engine shutdown or emergency shutdown. Many modern engines now use electronic controls, but most older and even some newer motors use the tried-and-true push/pull cable connections. These tend to be very reliable but do require periodic inspections to ensure they will operate when needed most. Let’s face it: Shift cables generally fail while docking, a time when they are needed most. Start by checking the cable attachment at the engine, and make sure the clamps securing the cable to the engine are tight and secure. Again, vibration can cause these attachments to loosen over time. Follow the cable along its run through the boat to the helm. Inspect the cable outer jacket for cracking or rust weeping through; these are signs it is due for replacement. Make sure the cables are not chafing on any motor or boat parts. Pay particular attention to cables passing close to hot exhaust pipes, as this can cause melting of the plastic cover. Do not overlook the control heads at the helm — these should be inspected and lubricated periodically as well. Make sure the levers operate smoothly and are positioned correctly. Also, with the engine stop engaged, check that the neutral safety is operating to prevent the engine from starting in gear.

A broken clamp for a shift control cable.

Don’t forget to check the propeller shafts and stuffing boxes. The days of the old flax-type stuffing box are giving way to modern dripless seals. These new seals do keep your boat drier and require less maintenance, but they still need attention. Dirt and oil are not friends of these newer seals, which are still installed on a flexible hose to the shaft long. Make sure the area around the seals is clean and free from dirt, oil and corrosion. Look for cracks around the seal housing or in the seal itself, check all hose clamps for rust and corrosion. Make sure no hoses or wires are near the seal or shaft.

Check the engine shaft coupling as well. Look for signs of rusting or loose bolts. Inspect the shaft to see if there is evidence of it slipping back in the coupling. Using a wrench, check the tightness of set screws and bolts. I also like to put the engine in gear while at idle to see if there is any wobble or run out when the shaft is turning slowly, a good way to see if the coupling may need realignment.

Engine mounts do not last forever, and problems with the mounts can translate into problems with vibration that could cause damage to shaft seals by allowing excessive movement. Motor mounts are easily checked while underway. Bring the boat to a full stop and while an observer is in the engine compartment, have the operator place the gear in reverse and give a short burst of hard reverse. Watch for any movement of the engine mounts. Look to see if the engine pulls back or torques to the side. Also watch for any bouncing or movement up and down as the throttle is applied. For twin-screw boats, do one engine at a time. Some movement is normal, but anything more than a little may be an indication the mounts are at the end of their life. Also check for excessive rusting or corrosion, particularly on any mounts under water pumps that may have leaked. Rusting can weaken the mounts and make alignment difficult.

A shaft seal with broken and missing hose clamps. Note that the hose is beginning to slide off the seal.

Finally, if the engine compartment has an automatic fire suppression system, give that a quick look over. Check the overall condition and make sure the gauge is still in the green. Check any wires or manual releases as well. I once surveyed a 16-year-old boat that still had the safety pin in place from the factory.

Most of these suggestions really only take a few minutes to do but can save you from expensive repairs or failures that affect the safety of your vessel.

Wayne Canning is a marine writer, photographer and surveyor. His website is

By Ocean Navigator