Car Overheating: Causes, What to Do, and Repair Costs

The temperature gauge is climbing and you are still two kilometres from the next exit. That is the moment this post is written for. Unlike a check engine light you can ignore for weeks, a rising temperature gauge gives you minutes before damage that was not there this morning becomes permanent. You have time to act - not much, but enough if you know what to do.

What should I do right now if my car is overheating?

If the temperature gauge is in the red or climbing rapidly, follow these steps immediately:

Turn off the A/C and turn the heater to maximum. The heater core acts as a secondary radiator. Running the heater at full blast with the fan on high pulls significant heat from the engine coolant. Yes, you will be uncomfortable. It is worth it. Pull over safely. Find the nearest safe stopping point. Do not try to reach a destination. Do not drive "just a few more kilometres." Every minute of driving while overheating compounds the damage. Turn off the engine. Once stopped, shut the engine off. Pop the hood to allow heat to escape, but do not touch anything under the hood. The cooling system is pressurized and extremely hot. Wait. Do not open the radiator cap or coolant reservoir while the engine is hot. Pressurized coolant at 100+ degrees Celsius will spray out and cause serious burns. Wait at least 30 minutes, ideally until the temperature gauge returns to the cold zone. Check coolant level. Once cool, check the coolant reservoir. If it is empty or low, the most likely cause is a coolant leak. Top up with water as an emergency measure to get to a shop (proper coolant mix should be used for long-term). Look under the car for puddles or drips. Do not restart and drive if the engine overheated severely. If the gauge was pegged at maximum, if you saw steam, or if the engine stalled from heat, call for a tow rather than risking further damage. A stalled engine that will not restart after overheating has its own failure chain - see car won't start troubleshooting for what to check next.

What causes engine overheating?

Low coolant from a leak. The most common cause. The cooling system is sealed, and coolant does not evaporate under normal conditions. If the level is low, there is a leak. Common leak points:

• Radiator (corrosion holes, cracked plastic end tanks)
• Radiator hoses (cracking with age)
• Water pump (weep hole leak or seal failure)
• Heater core (coolant smell inside the cabin)
• Head gasket (internal leak, coolant enters cylinders)

Failed thermostat. The thermostat is a valve that opens when the engine reaches operating temperature, allowing coolant to flow through the radiator. When it sticks closed, coolant circulates only within the engine block and never reaches the radiator to cool down. This is one of the most common and cheapest overheating fixes. Replacement: 80-250 euros. A stuck-closed thermostat often sets a P0128 coolant temperature code before overheating becomes visible on the gauge - a useful early warning if you are running an OBD2 scan regularly. Failed water pump. The water pump circulates coolant through the engine and radiator. When the impeller erodes (common on plastic impeller pumps), the bearing fails, or the seal leaks, circulation drops and the engine overheats. Replacement: 200-600 euros. On engines where the water pump is driven by the timing belt, it is commonly replaced together during timing belt service. Blocked or damaged radiator. External blockage (bugs, leaves, bent fins) reduces airflow. Internal blockage (corrosion, sediment) reduces coolant flow. A pressure test and flow test identify radiator issues. Replacement: 200-600 euros. Failed radiator fan. The electric radiator fan turns on when coolant temperature rises above a threshold, typically at idle or low speed when there is not enough airflow from driving. A failed fan motor, blown fuse, or faulty temperature switch means no cooling at idle. The car may be fine at highway speed but overheat in traffic. Blown head gasket. The head gasket seals the cylinder head to the engine block. When it fails, coolant can leak into the cylinders or combustion gases can enter the cooling system (overheating, bubbles in coolant reservoir). White exhaust smoke is one of the most reliable early signs - the exhaust smoke colors diagnosis guide covers the full spectrum of what each color indicates. Head gasket replacement: 800-2,500 euros. Air in the cooling system. After any cooling system repair, air pockets can prevent proper coolant circulation. Bleeding the system removes trapped air. This is a free fix if you can do it yourself, or 30-80 euros at a shop.

How do you diagnose an overheating engine?

Step 1: Check coolant level. Engine cold, open the reservoir cap. If low, top up and look for leaks. Check under the car for puddles, then trace the hoses, water pump, and radiator for drips or staining. Step 2: Check the thermostat. Start the engine cold and feel the upper radiator hose. It should stay cool until the engine reaches operating temperature (usually 80-90 degrees), then get hot as the thermostat opens. If it stays cool even when the gauge shows hot, the thermostat is stuck closed. Step 3: Check the radiator fan. With the engine at operating temperature and idling, the electric fan should cycle on. If it never turns on, check the fuse, relay, fan motor connector, and temperature switch. Step 4: Pressure test. A cooling system pressure test (any shop can do this) pressurizes the system and reveals external leaks. Internal leaks (head gasket) require additional testing. Step 5: Check for head gasket failure. Four signs point to an internal leak: white creamy residue under the oil filler cap (coolant mixing with oil); persistent white exhaust smoke even after the engine warms fully; bubbles surfacing in the coolant reservoir while the engine runs; and coolant loss with no external puddle beneath the car. A combustion leak tester (chemical test kit) definitively confirms or rules out head gasket failure.

Skanyx monitors coolant temperature in real time through live data and can alert you to abnormal temperature trends before the gauge reaches the danger zone. skanyx.com/download

Repair costs

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

The cost escalation is dramatic: a 20-euro thermostat ignored for a month becomes a 2,500-euro head gasket. Every overheating episode causes cumulative damage. Fix the root cause on the first occurrence. Seasonal cooling system checks - flushing old coolant, inspecting hoses, and testing the thermostat before summer - are the cheapest insurance against landing at the bottom of this table. If you are doing the work yourself, the DIY car repairs guide covers the right tools and safety steps for thermostat and hose replacement.