Main Engine

Air Filters

Air Filters are fitted to Diesel engines to stop air-borne contaminants from being sucked into the engine during combustion.

There are three main filters in general use, off-the-shelf disposable elements. The washable foam element. And the steel cartridge to be cleaned in oil. There are many more variants of the above. After removing the filter, give the air filter box a good clean with a dry clean cloth.

Main Engine Coolant Tanks

There are several different designs of main engine coolant cooling tanks. The cooling tank can be designed to fit over a part of the underwater section of the boat interior. The hot coolant transfers its heat through the hull to the cooler water outside.

The other method is cooling tubes running along outside the bottom of the boat hull. Then there is the matrix system of coolant pipes in a box section. This tank is filled the same way as any engine cooling system through the filler cap on top of the main engine; some systems have a coolant header tank complete with sight glass.

Main Enginer Drive Belts

Check drive belts regularly. Check belts are at the correct tension, with 'V' belts by pushing the belt in the middle of the longest span, no more than about half an inch or 12 mm.

With wide flat belts, twist the middle of the longest span to 90 degrees; any further, and it needs tightening. Check behind the pulleys looking for belt dust indicating belt wear. Have spare drive belts available in the spare parts locker.

Main Engine ECU (Electronic Control Unit)

An ECU, through its sensors on the engine, can make decisions independently to increase  performance and reduce emissions by regulating and altering the fuel, air, and injection timing. Check in the manual for the location of sensors and to periodically inspect them.

Main Engine Fuel Tanks

Fuel tanks can be manufactured from steel, aluminium, plastic or stainless steel. A DC electric level sender can check tank levels, a sight glass showing the actual level or a piece of hardwood that fits down the filler pipe to the tank bottom. All three systems work very well. The fuel tank layout on a boat is different from boat to boat. Some boats will have one tank; others will have two tanks (port & starboard) linked by a balancing line; with this system, the main engine fuel return must go to the tank from which the fuel supply is taken.

Periodically check the air vent gauzes are in place and not blocked. Check the deck filling caps are clean and 'O' rings in place. Ensure filler caps are tight (the main source of water entering the tank if caps are not tight).

Some tanks will have a drain cock fitted at the lowest point. This drain cock is ideal for draining off water and sediment periodically.

The main engine fuel supply shut-off cock, close to the tank and before the primary filter. This shut-off cock can be linked to an emergency shut-off system on the upper deck, a requirement for commercial operators. The fuel return line from the engine to the tank does not have a valve fitted. Keep a fuel filling log up to date with dates and locations of filling etc.

Main Engine Gearbox

The dipstick on your gearbox is sometimes difficult to read because of the clearness of the oil. Try filing the flat edge of the dipstick with a course file. Following your maintenance routine,  change the oil in the gearbox, and inspect the gearbox linkage.

Main Engine Lubricating Oil Filter

An oil and filter change is carried out per your maintenance plan, and extra oil is kept onboard for daily filling or an oil change. Spare filters should be available in the spare parts locker.

There are three ways to drain oil on the main engine. One by using the pump at the side of the engine. The second is by unscrewing the sump drain plug under the engine, which is virtually impossible. Thirdly, a vacuum pump down the dipstick tube.

Remember to have rags available, a cartridge removal tool and a plastic bag to put around the filter cartridge when unscrewing it; when replacing the filter cartridge, smear a drop of fresh oil around the cartridge seal.

Main Engine Raw Water Pump

Draws cooling water from outside the boat sends it through a heat exchanger to cool the engine coolant.  A spare impeller should be readily available aboard. Have the removal kit available or your preferred tools to remove the impeller.

Main Engine Spares

The main engine and associated equipment on the Primary Engine System should have a spare parts inventory list - and spare parts to be kept in dedicated and easy to get at lockers.

Main Engine Stern Glands

Various stern gland arrangements ensure the boat is dry as the propeller shaft exits the boat. The Traditional system of greased packing around the prop shaft held in place by a collar, with securing nuts that allow a drip or two of water, is still used today. The stern gland greaser is an integral part of the gland system and should be turned daily when cruising.

Modern types of stern glands are the 'Lip Seal' and 'Face Seal'; these seals are known as dripless seals; and some have to be squeezed to release the air trapped in the seal, especially if the boat has been out of the water or is on a drying berth before running the engine and turning the prop.

These seals occasionally need a little grease squeezed under the seals, check your manual.

Main Engine Control Cables

Check control cables are not too finely bent or caught on a sharp object. Check connections to the helm, main engine, and oil sliders as necessary.

Main Engine ECU - Get me home mode

If the ECU picks up a problem, it could reset engine speed to 'get me home' speed which is slow. Check this speed occasionally; manually setting the ECU to 'get me home mode' may feel it is too slow in an emergency, especially in bad weather conditions. Check the manual on overriding the ECU and tweak the speed..

Main Engine - Engine Mounts

Check Engine Mounts are clear of any debris, and the nitrile/rubber insert is clean and free of splashed liquid.

Main Engine Exhaust (wet & dry)

There are two types of exhaust systems in the boating world; the first one is the dry system, where cooling water does not mix with the exhaust, the same as a car. The second one is the wet exhaust, where the raw water after engine cooling exits with the exhaust.

Check exhaust systems looking for rust etc.; remove the first bend and check the inside, this is the first bend on a wet exhaust system and is liable to rust.

Main Engine Fuel Lines

Check fuel lines from the main engine to the tank, especially flexible ones that go over engine beds; check for rubbing on the underside of the fuel line. If there is evidence of wear, support the fuel line by using a short length of clear plastic flexible pipe cut down the length and placed over the fuel line. The fuel line sits in the tube protected from the engine bed etc.

Main Engine Hydraulic Oil System

The main engine hydraulic pump supplies pressure to operate the bow and stern thrusters, various winches and hydraulic lifts from a pump at the front of the main engine. The header tank is generally close by in the engine room, with a filter assembly that needs changing when maintenance is due. Spare filters and hydraulic oil are to be kept in the spare parts locker.

Main Engine Instrument Panel

Periodically check all connections on the panel and the main engine. At the end of the season, spray WD40 around the back of the panel.

Main Engine Hydraulic Oil System

The main engine hydraulic pump supplies pressure to operate the bow and stern thrusters, various winches and hydraulic lifts from a pump at the front of the main engine. The header tank is generally close by in the engine room, with a filter assembly that needs changing when maintenance is due. Spare filters and hydraulic oil are to be kept in the spare parts locker.

Main Engine Lubricating Oil Testing

There are several methods to test the oil in your engine. One method is to buy a packet of test papers that indicate water etc., in the oil sample, but this is not very successful. Imardex-marine can carry out oil sampling; contact us on the email contact at the bottom of the page.

Main Engine Thermostat

Thermostats are temperature-regulated valves fitted on the cooling system to open and shut allowing an internal combustion engine to warm up quickly. On initial start up the thermostat is shut as the engine warms up it slowly opens allowing cooling water to continue around the system and through the heat exchanger.

Air Filters

Air Filters are fitted to Diesel engines to stop air-borne contaminants from being sucked into the engine during combustion.

There are three main filters in general use, off-the-shelf disposable elements. The washable foam element. And the steel cartridge to be cleaned in oil. There are many more variants of the above. After removing the filter, give the air filter box a good clean with a dry clean cloth.