keeping them running
Page 53
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by Tony Wilding
Ways of improving engine cooling characteristics are often in the news these days. It has always seemed strange to me to leave everything to a simple thermostat which does nothing more really than provide for quick warming up. Having the coolant going continuously through a radiator designed for the worst possible conditions —high ambient temperatures, following wind, etc—provides far too much cooling especially when outside temperatures are low so usually coolant enters the bottom of the engine far too cold.
There are various ways of improving the sitUation, one of them being by fitting a thermostatically controlled fan such as that made by Dynair Ltd, Nailsworth, Glos. When I tested a Bedford fitted with the Dynair fan drive last year I found that it made worthwhile differences to temperatures in the engine. When unladen the fan was needed hardly at all, the temperature gradient across the engine was reduced and the general temperature throughout the engine was kept closer to the optimum.
Now Dynair has extended the range of equipment it offers and can now supply kits for engines with fans up to 28in. diameter. And all versions of the equipment now -fail safe" so that in the event of failure in the air-operating system full drive to the fan comes in automatically
regardless of engine temperature.
Latest in the Dynair range is the P42 which has been approved by Rolls-Royce and has already been fitted by Seddon and Scammell to some heavy tractive units. The P42 will supplement the P25 which is suitable for use for fans up to 19.5in. diameter as employed by Bedford, Ford and Leyland and on Perkins engines.
Like the P25, the P42 is produced as a kit comprising a patented fan-drive hub with air-operated clutch and a temperature sensing control valve which regulates the air supply to the fan drive according to the temperature of the engine coolant. Shaft-drive versions of the equipment intended primarily for pay applications are also available. These are already offered as options on the Leyland Leopard and Panther and on AEC Swift and Sabre psv.
The "fail safe" feature comes from a change in the operating system, air pressure now being used to keep the clutch open and therefore the fan drive inoperative until the engine temperature exceeds the optimum operating temperature. Then the air supply is cut off, the drive engages and the fan is continuously driven until temperature falls to a predetermined level; like the maximum setting this is fixed according to engine requirements.