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Preparing Your Fleet Vehicles for Hot-weather Driving

As temperatures increase during summer months, the demand placed on motor vehicles (and their engines in particular) increases significantly with the risk of engine failure elevating.
Preparing your fleet vehicles for hot-weather driving

As temperatures increase during summer months, the demand placed on motor vehicles (and their engines in particular) increases significantly with the risk of engine failure elevating. Engines rely on mechanical tolerances to produce power, oil to keep the contact surfaces separated, and coolant flowing through the engine to the radiator for cooling. Should any one of these critical elements fail, then engine failure is imminent.

Mechanical tolerances

Signs of worn engine components can normally be heard in the form of knocking, grinding or squealing noises as a result of metal components colliding or rubbing. By design, no rotating metallic parts are designed to collide or rub together. Therefore, when sounds like these are present, it is time to have your engine checked by a mechanic.


There are many different types of engine oil. Choosing the correct oil will depend on the engine type and ambient temperatures.

Gasoline engines can subject the engine oil to temperatures of up to 160°C. Choosing the right oil depends on the cold start temperatures as the correct oil will be able to sufficiently lubricate the engine at an ambient temperature as well as when the engine reaches normal operating temperature. The method for selecting the correct oil is to refer to the viscosity rating on the packaging and ensure that the oil operating temperature range is within the ambient temperature range.

Diesel engines rely on the compression of diesel fuel and oxygen to a point where the pressure is so great that combustion occurs, leading to the engine oil being exposed to temperatures of up to 315°C. In addition to this, the diesel fuel is not as pure as gasoline and contains more contaminates. Diesel engine oil is designed to deal with the higher compression and generally contain more detergents to assist in removing impurities left behind from the diesel fuel.

Cooling system


Healthy coolant will be free from minerals, non-acidic, and contain anti-iodizing agents to prevent corrosion as well as other agents to lower the freezing temperature. Coolant degrades over time and may require replacement. Follow the owner's manual for recommendations on how frequently the coolant should be changed. Never mix different types of coolants as this can lead to chemical reactions and damage to the cooling system.

Cooling systems rely on pressure to increase the boiling temperature of the coolant. The higher the pressure, the higher the temperature before the coolant starts to boil. For this reason, the radiator or coolant reservoir should never be opened while the engine is hot, as the pressurized coolant can cause serious burns.

Should a leak develop in the cooling system, this presents two issues. The first is that the loss of coolant will introduce air in to the cooling system, which acts as an insulator and prevents heat from being transferred to the radiator. Secondly, the leak will lead to a loss in pressure, causing the boiling point to lower and further complications to develop.

Your mechanic can conduct a cooling system pressure test to ensure that there are no leaks and that the system can hold pressure.

Water pump

The water pump is vital for pumping the coolant around the engine and into the radiator for cooling. Water pumps are normally powered by a belt driven from the engine's crankshaft. For this reason, all belts should be checked for condition to ensure they are free of cracks and tight enough to not slip. Noisy or leaking water pumps should be checked by your mechanic asap.


The radiator is critical for transferring heat from the coolant into the air. Radiators require good airflow across the fins for the heat transfer process to take place. The radiator needs to be cleaned regularly to eliminate build-up of dust and other foreign objects than prevent the air from flowing over the fins. Lastly the radiator may look clean from the outside but be partially blocked on the inside. Part of the vehicle's regular maintenance program should include a radiator flush to ensure the coolant can flow freely.

Cooling fan

The radiator is cooled by a fan, some vehicles use a fan driven by the engine, some use an electric thermo fan, and some use both. When the vehicle is stationary or travelling at low speed, the fan provides the necessary airflow over the radiator fins to provide cooling. Should the fan fail or the air flow ducts become blocked then the vehicle should be checked by a mechanic asap.


Often forgotten, the thermostat plays a critical part in the engine cooling system and engine performance. Since engines work more efficiently at normal operating temperature, the thermostat's job is to prevent the coolant from leaving the engine block until the operating temperature is reached. Once the temperature is reached, the hot coolant flows to the radiator and the cooler coolant flows into the engine block, providing cooling while the hot coolant cools in the radiator. This cycle continues at a steady pace while the engine is running to maintain a constant temperature and allow time for the coolant to cool in the radiator.

A thermostat may fail in the open position, which means the coolant continually flows through the engine clock, with radiation increasing the time for the engine to warm up and decreasing the time that the coolant has to cool in the radiator. This leads to a slow constant increase in temperature and, on hot days, will eventually lead to an overheating situation.

Alternatively, thermostats can fail in the closed position, which prevents the coolant from leaving the engine block, resulting in rapid overheating.

Battery life

Another common misconception among drivers is the effects of weather on batteries. Although cold weather does have adverse effects on them, it is heat that can be more destructive. Whereas the average car battery has a lifespan of three to three and half years, batteries in vehicles exposed to continuous high temperatures tend to not last as long.

Simple steps to help prolong your battery's life can include:

  • Cleaning the battery. Dirt can quickly build up, especially in rough desert terrains, and this will result in draining the power in the battery. Use a wire brush to clean the terminals, and baking soda dissolved in water to clean the battery itself.
  • For larger, heavier vehicles that require batteries to be refilled with water, check the levels regularly -- especially during the summer months -- and, where possible, refill with distilled water.
Preparing Your Fleet Vehicles for Hot-weather Driving
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