Engine Cooling System

(Notes taken from Op Notes 2012)

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Description: The boat has a complex cooling system. Firstly an internal fresh water system provides cooling for the engine. This system may require occasional topping up with clean fresh water via the radiator cap clearly visible below the cockpit hatch. Water (in the fresh water cooling system) is heated by the engine, regulated by the thermostat and pumped, firstly to the calorifier where heat is transferred to the domestic hot water. The coolant is then piped to a heat exchanger (which is attached to the engine  - see manual photos), where any residual heat of the coolant is dissipated before being returned to the cylinder block.

 

The Calorifier: (through which the engine’s fresh cooling water is circulated), is located behind the hatch at the rear of the aft cabin. A single isolation valve is located in the engine compartment. The calorifier is fitted with a pressure relief valve and a 240-volt immersion heater the switch for which is located near the battery controls. Two valves adjacent the calorifier can isolate the cockpit shower.

 

The Heat Exchanger: (Renewed in Jan 97) is cooled by raw sea water drawn from the coolant seacock (below aft cabin berth) and pumped through the heat exchanger before being discharged at the transom. The heat exchanger also incorporates an oil cooler.

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Raw Water Pump: raw water is circulated by a pump mounted on the timing gear cover (rear of the engine) and is driven at half speed from the fuel pump gear. The raw water pump will, from time to time, require renewal of the impeller (Spare on board – Bosun’s Locker). Pump Jabsco 3270-200 Old Impeller reference number was  1210-0001. Code change to 3085-001. Alternative: CEF 500 107 GT.  Agent Cleghorn Waring & Co (Pumps) Ltd. Tel: 01462 480380. Fax 01462 482422. Email mail@cleghorn.co.uk.

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The Fresh Water Pump: and the alternator are belt driven from the crankshaft pulley. A fresh water pump and a spare drive belt are on board. Both water pumps are fully described in the Perkins manual.

 

Some likely causes of engine overheating:

1. Loss or restricted flow of the Fresh water coolant:  Loose jubilee clips, split water hoses,         leaking water pump, broken drive belt, low water level, dirt/ sludge causing partial blockage              of the water ways, faulty thermostat or faulty water filler cap.

2. Loss or restricted flow (check flow at the stern pump out) of the Raw water coolant:               Blocked strainer (external hull fitting), closed Seacock, loose jubilee clips, split water hoses,         dirt or sludge causing partial blockage of the heat exchanger, worn raw water pump impeller.

3. Blown cylinder head gasket. Initially this may be difficult to diagnose. Often, but not always,      causes water contamination of the engine oil, indicated by globules of water on the dipstick.             A blown gasket often causes the loss of fresh water coolant and/or a build up of steam          pressure causing swollen hoses. Perhaps slowly at first but the water loss and/or steam         pressure may quickly increase. Slow running (less than 1500 revs) for a couple of hours with               a blown cylinder head gasket is unlikely to cause serious damage providing engine temperature          is monitored and overheating can be controlled.

 

Engines, which suffer overheating, are quickly subjected to the following symptoms and damage:

An increase in temperature within the range of the temperature gauge. Further increase in temperature beyond the range of the gauge with a simultaneous steam pressure built up. This will quickly rupture hoses and/ or blow core plugs resulting in the total loss of fresh water coolant. Further rapid increase in temperature causing piston seizure followed immediately with catastrophic damage - Broken Pistons/ rings and/ or  crankshaft and/ or connecting rods, ruptured cylinder walls and mangled valve assemblies.