The car overheats whilst driving or idling: faults with the thermostat, water pump and cooling fan (Kirkkonummi–Veikkola)
A car overheats when the cooling system is unable to dissipate the heat generated by the engine efficiently enough. The temperature can rise whilst driving, in traffic or when the engine is idling, and the symptoms may be caused by, for example, the thermostat, water pump, cooling fan, radiator or a fluid leak. If the temperature gauge moves into the red zone or a warning light comes on on the dashboard…
Voit jättää meille soittopyynnön
Jätä nimesi ja numerosi, niin soitamme takaisin saman päivän aikana.
The car is overheating, when the cooling system is unable to dissipate the heat generated by the engine efficiently enough. The temperature may rise whilst driving, in traffic or when the engine is idling, and the symptoms may be caused by, for example, the thermostat, water pump, cooling fan, radiator or a fluid leak. If the temperature gauge moves into the red zone or the cooling system warning light comes on in the instrument panel, continuing to drive may damage the engine.
Overheating requires a quick but calm response. The driver should not open the expansion tank of a hot engine or try to force the car to a garage. The following guidelines will help you identify the most common types of faults and assess when it is safe to move the car to a safe place and when it needs to be towed.
Your car is overheating: what to do when you notice the first signs
Switch off the air conditioning and keep an eye on the temperature gauge. If the temperature has only just started to rise, setting the cabin heating to full power may divert some of the heat away from the engine. This is only a temporary measure to help you reach a safe place to stop. If the temperature continues to rise, the engine loses power or steam starts to come from under the bonnet, stop the car and switch off the engine.
Choose a place to stop where the car will not pose a danger to other road users. Switch on your hazard warning lights and use the warning triangle as required by the situation. Allow the engine to cool down naturally. Do not touch the expansion tank cap whilst it is hot, as the pressure in the system may cause boiling fluid and steam to be released.
Stop driving if you experience any of these symptoms. Just one serious symptom is enough to make you stop.
The thermometer is in the red. The engine temperature has exceeded the safe operating range.
Steam is rising from under the bonnet. The coolant may boil or leak under pressure.
The engine is running unevenly. Overheating may have affected combustion or the engine’s compression.
Coolant is leaking onto the ground. Driving with a low fluid level can cause costly engine damage.
Causes of overheating: thermostat, water pump and fan
The thermostat regulates the flow of coolant between the engine and the radiator. A stuck thermostat prevents hot coolant from reaching the radiator, which means the temperature can rise rapidly even when driving on the open road. The upper coolant hose may remain cooler than the rest of the engine, even if the temperature gauge shows a high reading. However, a faulty thermostat should not be assumed solely on the basis of the hose temperature, as the system’s design varies between car models.
The water pump circulates the coolant. A worn impeller, a faulty bearing or a leak in the pump will impair circulation. Symptoms may include overheating as the engine load increases, coolant seeping from near the pump, or a whirring noise coming from the bearing. In some engines, the water pump is part of the timing cover assembly, so a fault may also compromise the operation of the timing cover.
The cooling fan is particularly needed when the engine is idling and in slow-moving traffic, when the airflow from driving does not pass through the radiator. If the temperature remains normal on the open road but rises whilst queuing or parked, it is worth starting your checks with the fan, fuse, relay, temperature sensor and fan control unit.
| Oire | Likely area for inspection | Action required |
|---|---|---|
| The temperature rises both whilst driving and when the engine is idling | Thermostat, water pump or low fluid level | Stop driving and have the system checked |
| The temperature rises in traffic but drops on the open road | Cooling fan or its electrical control system | Have the fan checked at a garage |
| The temperature rises under heavy load | Water pump, blocked radiator or poor fluid circulation | Avoid overloading and book a fault-finding appointment |
| The heater blows cold air when the engine is hot | Fluid deficiency, air lock or circulation problem | Switch off the engine and check for any leaks |
You should not try to check the temperature of an overheated engine by driving it. A tow usually costs less than repairing the cylinder head or the whole engine.
Radiator faults and coolant loss
A radiator may lose its efficiency due to an external blockage, internal build-up or a leak. Leaves, insects and dirt reduce the airflow through the radiator. An internal blockage, on the other hand, prevents the fluid from circulating evenly. The fins of an old radiator may also corrode and only start to leak once the system has warmed up and the pressure has risen.
A drop in the fluid level is always caused by something, even if there is no puddle left under the car. The fluid may leak onto a hot engine surface and evaporate, enter the passenger compartment from the heater core, or find its way into the combustion chamber due to a faulty head gasket. A sweet smell, a pale residue on hose connections and a constant need to top up the fluid are all reasons to have the system checked. Further information on hard-to-detect leaks can be found in the article coolant loss without any visible puddle.
A brief note
A fault code can help in diagnosing a fan control fault, but the cooling system also requires an examination of temperatures, pressure and fluid circulation.
When does a car overheat to such an extent that you have to stop driving?
You must stop driving immediately if the warning light comes on red, the gauge rises into the red zone, you hear an unusual knocking sound from the engine, or steam is coming from under the bonnet. The same applies if the heater starts blowing cold air at the same time as the engine temperature rises. Cold air from the heater may indicate that hot coolant is not circulating through the heater core.
You can check the coolant level in a cold engine in accordance with the car’s owner’s manual. If the expansion tank is empty, there is a significant leak, or the coolant disappears immediately after topping up, do not start the engine. Topping up the coolant will not repair a faulty thermostat, pump or a leaking system. Use only the coolant specified by the manufacturer, as mixing different types of coolant can cause deposits to form.
Assess the situation before moving the car. If anything is unclear, call a tow truck.
Let the engine cool down. Do not open the expansion tank until the system has cooled down.
Check for any visible leaks. Look under the car and into the engine compartment, taking care not to touch any hot parts.
Pay attention to the warning lights. A red temperature warning means you must stop driving.
Be aware of the traffic conditions. You can also find out more about stopping safely In the Traffic Safety guidelines.
Cooling system troubleshooting in Kirkkonummi and Veikkola
At the workshop, troubleshooting begins with a visual inspection of the fluid level, signs of leaks, hoses and the radiator. The system can be pressurised, which makes even small leaks easier to detect. The opening of the thermostat and the circulation of the coolant are assessed by taking temperature readings. The fan’s motor, power supply and control signal are checked.
If the symptoms suggest an internal engine leak, the coolant can be tested for combustion gases. At the same time, the condition of the engine oil and coolant is checked. STS Evitskog serves motorists in the Kirkkonummi, Veikkola, Siuntio and Espoo areas at Kylmäläntie 350. Multi-brand garage workshop services cover the inspection of the cooling system and any necessary repairs for various car makes.
The extent of the repair depends on the fault found. Replacing the fan relay is a different job to replacing the water pump in conjunction with the cylinder head. It is advisable to confirm the cause of the fault by taking measurements before replacing any parts, to ensure that a functioning thermostat, pump or fan is not replaced unnecessarily. After the repair, the system is filled with the correct fluid, bled and tested at normal operating temperature.
Is the temperature in the car getting too high?
STS Evitskog investigates faults in cooling systems in Kirkkonummi. Book an inspection before overheating causes damage to the engine.