Yanmar 2GM20

Yanmar 2GM20 seawater pump. Cooling seawater enters from the tube on the left.

The 2GM20 series uses either a direct seawater cooling system, or an indirect freshwater cooling system (specified by the suffix letter F i.e. 2GM20F). Seawater is pumped into the engine through a seawater pump (impeller type). In the engines equipped with a direct seawater cooling system, seawater is used to cool the internals of the engine directly. The engines equipped with a fresh water cooling system have an additional heat exchanger, where heat transfer occurs between the seawater and internal freshwater.

The impeller of the seawater pump can suffer from wear and tear, especially when run dry for some period of time, in which case it has to be replaced to avoid loss in the flow of cooling seawater, a potential source of engine overheating.

A particularly difficult problem in tropical waters is jellyfish. Their tentacles can be sucked into water intakes. In extremes, it is possible for the rubber exhaust hose to catch fire, the plastic silencer to melt and the head-gasket to fail. In colder waters, boats are far less likely to meet such problems. The solution is to have a large basket-type water strainer and overheat alarms (standard on most Yanmar engines)

The seawater pump is rotated by a short belt linked to the crankshaft.

Yanmar 2GM20 fuel filter.

An inline fuel filter is easily accessible from the front part of the engine. The filter retains solid particles and separates water from diesel (as water is heavier than diesel, it will settle at the bottom of the filter), just before the diesel fuel enters the highly sensitive high-pressure fuel pump. The water inside diesel fuel can lead to rusting of the internals of the engine, as well as lubrication problems. The filter element is made of fluted paper with metal end caps.

When the engine has to be bled because air has penetrated into the pipes (usually after running out of diesel), it will usually be necessary to bleed the diesel filter: the top vent is unscrewed so as to let the excess air escape, while diesel fuel is pumped into the fuel filter with the manual fuel lift pump (just behind the yellow dipstick). The vent can be screwed shut when diesel fuel starts to gush out of it.

A primary fuel filter is usually installed upstream of the engine, so as to filter out the larger particles and filter a larger quantity of water that might be present in the fuel.

Every time a filter is disassembled or changed, it will be necessary to bleed it so as to remove excess air, again by opening the top vent so as to let diesel chase all the air (diesel fills up the filter either through gravity -usually the case for the primary filter- or with the help of the fuel lift pump -usually the case for the engine fuel filter-) and diesel starts to gush out. The vent should then be screwed shut.