Few things ruin a summer drive faster than watching your temperature gauge climb into the red, whether you’re heading away on holiday or simply commuting through stop-start traffic on a hot day. Understanding why your car overheats and what to do about it can save you from serious damage and costly repairs.

Why Your Car Overheats (Especially in Summer Heat)

The cooling system is responsible for maintaining engine temperature within a safe range. Here is how it works in simple terms:

• Coolant-a mixture of antifreeze and water-circulates through the engine block, where it absorbs heat from combustion.
• The water pump pushes coolant through the system. The thermostat regulates coolant flow based on engine temperature, opening to allow hot coolant into the radiator once the engine reaches its normal operating temperature.
• The radiator dissipates heat from the engine into the outside air, helped by an electric fan at low speeds. The system runs under pressure, which raises the boiling point of the coolant.

In summer, temperatures above 25–30°C shrink the temperature gap between the radiator core and ambient air, reducing heat transfer efficiency. Stop-start traffic cuts airflow. Running air conditioning adds load. Fully loaded cars heading to a summertime event or holiday push the car engine harder and generate excess heat. A small weakness, like a slightly sticking thermostat, stays invisible in mild weather but can cause the engine to overheat in the July or August heat.

The difference between a normally warm engine at its operating temperature and an overheating engine is straightforward: if the gauge sits in the mid-range, you are fine. If it creeps toward “H” or red, or the warning light illuminates, your car is overheating.

Immediate Steps if Your Car Is Overheating Right Now

If your car is overheating, seconds matter. Follow these steps:

• React to the first signs. A rising engine temperature gauge, a flashing temperature warning light, visible steam, or a sudden drop in engine power all mean the same thing: pull over safely, well clear of traffic. Turn on your hazard lights.
• Turn off the A/C and crank the heat immediately. Switching off air conditioning reduces engine load; turning the cabin heater to maximum pushes hot air away from the engine and into the cabin. It is uncomfortable but effective as a stopgap.
• Pull over safely and turn off the engine. Apply the handbrake. If you are on a busy road, get passengers out on the safe side, away from live traffic.
• Do not open the bonnet straight away. Never remove the radiator cap or expansion tank cap while the engine is hot. The system is pressurised, and boiling coolant can erupt, causing severe steam burns. Wait at least 30 minutes for the engine to cool-up to an hour in hot weather or after motorway driving-before inspecting anything.
• Avoid dangerous quick fixes. Do not pour cold water directly onto a hot engine or radiator. Thermal shock can crack the engine block or warp cylinder heads. Do not drive on “just a bit further”

Coolant should not be added to a hot engine to prevent damage. Patience here prevents big repair bills later.

Common Causes of a Car Overheating

Common causes of a car overheating include low coolant levels or a faulty thermostat, but the full list runs deeper. Here are the main engine problems to consider:

• Low or contaminated coolant. Low coolant levels can cause engine overheating because there is simply not enough fluid to carry heat. Old, sludgy, or incorrectly mixed coolant loses its ability to absorb and transfer heat effectively.
• Cooling system leaks. Leaking radiator cores, split hoses, loose clamps, or cracked expansion tanks drain coolant gradually. Look for coloured puddles under the car and a sweet smell near the front. A cooling system leak can lead to overheating before you notice the level has dropped.
• Malfunctioning thermostat. This can block coolant flow entirely. If stuck closed, the thermostat prevents coolant from reaching the radiator, causing rapid overheating-especially in traffic. Thermostat failure can lead to engine overheating while idling, often with the cabin heater blowing cold because coolant is not circulating. A thermostat can fail to open at any age, but risk increases past 60,000 miles.
• Broken water pump or slipping belt. A malfunctioning water pump can prevent coolant circulation. Worn impellers, seized bearings, or a snapped serpentine belt stop coolant flow dead, producing a sudden temperature spike and sometimes grinding or unusual noises from the front of the engine. A faulty water pump disrupts coolant flow and causes overheating rapidly.
• Damaged radiator or fan. Radiator issues can lead to car overheating. Crushed or bent fins, internal blockages from corrosion, electric fan motor failure, or a bad fan switch all prevent the radiator from shedding heat. Damaged radiator fins can prevent effective cooling, particularly at low speeds or idle where airflow depends on the fan.
• Blown head gasket. Combustion gases leaking into coolant passages cause constant overheating, white exhaust smoke, and a creamy “mayonnaise” residue under the oil filler cap-a sign coolant is mixing with engine oil. This is among the most expensive engine issues to resolve.
• Secondary factors. Low engine oil levels can increase engine temperature because engine oil reduces friction and heat in moving parts. 

Warning Signs Your Engine Is Overheating

Recognising the warning signs early can be the difference between a roadside top-up and a replacement engine. Watch for:

• Dashboard warning lights.
• Steam rising from the bonnet. 
• Distinctive smells. A sweet smell (like butterscotch) signals leaking engine coolant. Burning rubber points to a slipping drive belt. A burning smell from hot oil on exhaust components is another red flag. 
• Changes in engine behaviour. Rough engine running, hesitant acceleration, loss of engine power, or knocking and ticking unusual noises from the top of the engine as oil thins and engine components expand under heat.
• Bonnet too hot to touch. If you cannot hold your hand on the bonnet for more than a few seconds, the engine temperature is likely abnormally high.
• Air conditioning dropping out. Some cars automatically cut air conditioning when overheating to reduce load.

Is It Safe to Keep Driving an Overheating Car?

In short: no. Continuing to drive an overheated engine can result in expensive repairs- wiped cylinder heads, a cracked engine block, destroyed bearings, or a seized engine. A car overheating is not something you can safely ignore.

• If the temperature warning light is on, the gauge is in the red, or there is steam from under the bonnet, do not keep driving except to move the overheated car a few metres to a safe stopping point to avoid further damage.
• If you are stuck in a live motorway lane with no hard shoulder, shift into neutral when stationary, turn off air conditioning, turn the heater to full, and watch the car’s temperature constantly. Move to safety at the first opportunity.
• Common “tricks” like blasting hot air through the heater and opening windows are temporary measures only. They buy you a short window, not a fix for the underlying coolant system problem.
• If the car’s temperature keeps rising, stop driving. Call roadside assistance, arrange a tow truck, or use your breakdown cover. The cost of a recovery is a fraction of the serious damage and costly repairs from a seized or overheated engine.

Preventing Engine Overheating: Maintenance & Driving Habits

The best way to prevent engine overheating is routine attention to your car’s cooling system. Here is a practical schedule:

• Coolant care. Check coolant levels monthly to prevent overheating. Flush the cooling system every 2–5 years as recommended in the owner’s manual. 
• Thermostat, water pump, and belts. Replace the thermostat if it shows signs of sticking. Replace ageing water pumps and thermostats at manufacturer intervals, often between 60,000 and 100,000 miles. Inspect serpentine and auxiliary belts for cracks, glazing, or slack.
• Oil changes. Engine oil helps transfer heat away from the engine and reduces friction in moving parts. Regular oil changes prevent engine overheating. Most vehicles need oil changes every 5,000–10,000 miles-check your owner’s manual.
• Pre-journey checks. Before long summer drives, check coolant, oil, visible hoses, and fan operation the day before.
• Driving style. Avoid hard acceleration when heavily loaded or towing. Back off on long climbs and use lower gears rather than lugging the engine running at low RPM, which generates more heat with less airflow.
• Parking and environment. Park in shade where possible, use sunshades, and avoid idling unnecessarily in hot weather to keep under-bonnet temperatures down and your car cool.

Stay up to date with your cooling system maintenance and your summer trips will end at the start line, not on the hard shoulder.

CTA: Don’t hesitate to contact the team at Keston Car Care for any advice on overheating engines. 

Car Overheating FAQs

Can I use just water instead of coolant if my car is overheating?

Plain water works as an emergency top-up to get you to a garage, but it does not protect against corrosion, and its lower boiling point compared to a proper antifreeze mix means it cannot handle the same heat. Have the system drained and refilled with new coolant as soon as possible.

Why does my car overheat only when I’m stuck in traffic?

At low speeds or standstill, airflow through the radiator drops to almost nothing. The electric cooling fan and the car’s thermostat become critical. If the fan motor has failed, or if a thermostat fails to open properly, the engine overheats in queues but may run fine at motorway speeds where natural airflow compensates.

Does carrying bikes or gear on the roof affect engine temperature?

Absolutely. Roof racks and bike carriers add aerodynamic drag and weight, forcing the engine to work harder. On motorways and climbs in hot weather, this extra load can expose a marginal cooling system and push an otherwise healthy engine toward overheating.