Cold weather can cause starting woes

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IOL mot pic jun22 car trouble If cold sensor is faulty, the ECU acts as if the engine is warm and the cold start is not activated.

Starting problems are a pain in the neck on any car, especially in the cold weather we have had of late.

We had a car which would fire but refuse to run. However, after several attempts it would run and if left idling for a while could be driven. But if the throttle was pressed while the engine was struggling, it would cut out.

The trouble was due to a faulty temperature sensor. This sensor can be easily checked with an ohmmeter.

The electronic-control unit relies on information from this sensor. When the engine is cold, the sensor sends the cold signal to the cold-start mechanism, but if the sensor is faulty, the ECU acts as if the engine is warm and the cold start is not activated.

A new temperature sensor was fitted and from then on starting was easy.

Following that, perhaps a few words on how the liquid cooling system operates and the need for antifreeze might be helpful.

Coolant circulates through the cylinder block, up through the head and back through the bypass to the water pump when the thermostat is closed.

When coolant temperature reaches thermostat operating temperature, coolant circulates from the water pump to the cylinder block and cylinder head then through the open thermostat to the radiator through which it passes and back to the water pump.

The liquid coolant absorbs heat while in the engine and transfers it to the radiator where the heat is dissipated in the air.

Water is great for the job, but has some shortcomings. Its boiling point is relatively low therefore it freezes easily. Also, water requires additives and inhibitors to prevent, or least retard, rust and scale from forming, and to keep the water pump seal lubricated.

We must bear in mind that these additives and inhibitors have a finite life and, for this reason, it is recommended that the antifreeze is renewed every 12 to 24 months.

A mixture of 50 percent undiluted ethylene glycol antifreeze and 50 percent water will provide freeze protection as low as minus-36 degrees C and has the previously mentioned inhibitors and additives. It has a higher boiling point than water, about 110 degrees C at 101.4 kilopascals atmospheric pressure.

Use only the mixture recommended by the manufacturer.

Too much ethylene glycol may cause antifreeze to thicken at low temperatures, thus inhibiting coolant circulation and possibly causing antifreeze in the engine to boil.

Pressurising the cooling system raises the boiling point of the coolant by about 1.8 degrees C for every 6.895 kilopascals (kPa). Pressurising reduces the tendency to boil.

For example, a 68.95kPa radiator pressure cap will increase the boiling point of a 50:50 solution from 110 to 128 degrees C.

The system becomes pressurised due to coolant expansion and the radiator pressure cap has a relief valve to limit pressure to a predetermined level.

When the engine is stopped and the coolant begins to cool down, a low pressure is created in the cooling system and coolant re-enters the reservoir through a vacuum valve in the pressure cap. This prevents radiator hoses from collapsing and allows the system to remain full at all times. - Star Motoring

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