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Many Freeman engines are directly cooled, i.e. the water flows from the sea cock, around the exhaust manifold and out of the exhaust.

Whilst indirectly cooled engines virtually always have a thermostat within the system, this is not the case with direct cooled engines, particularly the earlier models.

For WaterMota petrol engines only fit a very low temperature thermostat (up to 75 degrees), normal thermostats found in most cars break at a too higher temperature. The sudden contrast in temperature between the cold river water and the temperature at which the thermostat breaks can seriously damage the engine.

Therefore on an engine that has not previously been fitted with a thermostat it is important not only to fit the correct thermostat, but also to ensure that there is a bypass and that it is operational. For WaterMota engines the bypass and thermostat setup is shown in the engine handbook.

The reasoning is quite simple, a car has a circulating pump, a boat has a full pressure pump. The pressure pump sucks the water constantly from the river and passes it through the exhaust out of the boat. When the thermostat is closed, while the engine heats the water, unless there is a bypass the constantly running pump builds up pressure and something has to give!

There is a lot of discussion about relief holes in thermostats, basically the WaterMota Sea Panther and some Perkins engines were designed to require a relief hole or valve in the thermostat. The WaterMota Sea Tiger and Sea Wolf engines were not.

Whilst drilling a relief hole in the thermostat may help the immediate problem, it may be treating the symptom rather than the cause! Often it is really the lack of, or the improper functioning of, the bypass valve that is really the problem. Also look for a build up of calcium in the head as this can also restrict the true water flow.

An additional hole in the thermostat will probably not cause any further problem but has it really solved the original problem?

All of the above assumes that if you do have a problem with the water cooling you have previously checked the standard routine items such as the water pump impeller, sea cock filter and that you have looked for restrictions, blockages or even air leaks in to the system.

The Freeman Owners Helpline (01491 652085) is available to Club Members after 4pm to discuss individual problems if required.