Some of the many things that should be checked are:

• Thermostats
• Lubrication system
• Poppet valve
• Fuel System

Every 100 hour service must include the replacement of the raw water pump impellor. Its function is drawing sea water into the engine for cooling purposes and maintaining its normal operating temperature. The blades of the rubber (or in some cases nitrile) impellors, being compressed for a long duration of time, cause a “set” of the impellor blades, thereby causing the pump to develop less volume and/or pressure needed to circulate cooling water through the engine. Sometimes this “set,” depending on its severity, can cause either a low speed or a high speed overheat. The impellors also become dry rotted and may disintegrate causing the engine to overheat. Water pump impellor replacement is a MUST every year to assure that no internal/expensive damage happens to the engine.

Your 100 hour service continues in the cooling system with the replacement of the thermostat(s). This not always done in an inboard engine, but most definitely should be done to an outboard that is continually run in salt water. Thermostats, on an outboard engine, serve two purposes. The first is the most obvious use, to maintain the engines normal operating temperature by opening and closing, allowing water to flow through it at the manufacturers designated temperature. The second function is to restrict the water flow so that the water will flow to the top of the power head, and so that the water will fill every available cavity in the water passages of the engine, thus cooling all of the metal surfaces in the water passages. The reason the thermostats need to be replaced or checked is that corrosion tends to create a blockage of water flow through the thermostat housing. Even if you flush the engine with fresh water after each use corrosion still develops within the cylinder head and housing. The thermostats may be in good operating order, but they still may be corroded and less effective at performing their function. Thermostats are rather inexpensive items and it is therefore good insurance to replace them once per year, whether you think they need it or not.

Similar to the function of the thermostat is a cooling system component called the poppet valve. While the thermostats restrict the water at low engine speed, the poppet valve restricts water at high speed allowing the water level to be maintained all the way to the top of the outboard power head. The movement of the valve, open and closed, is done with a spring and rubber diaphragm. Corrosion usually develops around the rubber diaphragm causing it to leek or to become deteriorated which will in turn result in a possible high speed overheat. Once again, it is cheap insurance to replace this valve once a year. This concludes the cooling system aspect of the 100 hour service.

Lubrication

It is also important each year to service the gear case. This entails draining the gear lube and examining the condition of the oil. If the oil comes out black or its original color, this would be normal. If you see excessive metal in the oil, there is excessive wear on the gears which would require disassembly and further examination. If the oil comes out milky or very little comes out at all, then the seals on the drive shaft, shift shaft, and propeller shaft and or the seal surfaces may be worn. If this is the case, a technician then performs a positive pressure test or a negative test (vacuum test) to determine where the leak is occurring. If a leak is detected, it is usually wise to reseal the entire unit. In the oil looks normal, the unit should be filled with fresh oil as per the manufacturer’s specifications. Next the prop shaft is greased so that it may be removed and replaced easily in the future.

If the engine is a four stroke outboard, then the crank case oil and filter must be changed. It is always best to use manufacturers (oem) parts for this service. Note: Engine manufacturers vary the specifications and types of oils to be used. It is important for the technician to refer to the owner’s/repair manual when performing this task.

For two strokes, the engine oil is either premixed or injected by a pump on the power head. TCW3 two cycle oil is used on most two cycle outboard engines; however, direct fuel injection or DFI requires special oils that reduce carbon build-up around the injectors. Knowledge of manufacturer’s specifications are required on all DFI engines.

There is an inline oil filter that must be replaced to ensure the proper flow of oil to the oil pump. The technician should also check the levels in the tanks and make sure they are full or topped-off and check hoses of the oiling system and replace them as necessary if dry rot is detected.

Fuel System:

Fuel filters must be removed and a fuel sample be taken to determine the condition of fuel in the tank. Often times water and other contaminates are found in the fuel. The fuel filter should be replaced each year. Excessive contaminates are cause for additional service to fuel tank i.e. polishing fuel, cleaning tank, etc.

Next your fuel line/primer bulb is examined to determine if there is dry rot. Fuel lines and primer bulbs are replaced as needed. All fuel filters will be replaced including the ones found on the power head.

Compression & Spark Test

Spark plugs are removed and examined for excessive wear and excessive carbon buildup and/or piston material. Each cylinder is tested for the amount of compression it is able to produce. Also a spark test is performed to assure proper function of the ignition system.

Electrical System

All electrical connectors at batteries are examined for corrosion and proper tension. Batteries are tested for proper electrolyte level and load. Complete check of the running system i.e. running lights, bilge pumps, other pumps and electronics are checked as well.

Once done, the annual service will not only enable you to have fuel efficiency, but will give you the confidence that your boat is operating properly ultimately giving you hours of safe, fun boating. Preventative maintenance can ensure that your boat always performs its best which will make your boating experience more pleasurable.