Remember the old habit ofля Gazelle drivers keeping a plastic bottle handy to prop the hood slightly open? Even if it’s less common today, engines still overheat, and the consequences can be more serious.
The close fit between a cast iron block and an aluminum cylinder head means their thermal expansion rates differ, so overheating can warp the head and cause head gasket failure. Thin-walled sleeves can also deform under excessive heat.
At the first sign of overheating, stop the car quickly and safely.
But overheating isn’t always sudden.
Instant or slow?
Overheating is like a family quarrel. Some bursts occur without warning, while others build up through gradual strain. The engine can creep toward a dangerous temperature threshold day after day, or it can flare into the red zone without much notice.
Slow but sure
Excessive load is a common culprit. An interior packed with cargo, a trailer hitched to the back, or a roof rack can push temperatures higher, especially in summer. City driving may feel fine, but once on the highway the cooling airflow isn’t enough and overheating follows. The solution is simple: reduce the load and slow down.
Steep road climbs and mountain driving can create a similar risk. Low gears, high engine load, and thin air raise temperatures steadily, making a stop necessary.
Low coolant levels are another frequent cause. If the cooling system is in good condition and leaks are absent, coolant can still drop due to evaporation, particularly when counterfeit products are used. When the level falls, circulation weakens and may stop, risking a warped cylinder head. Monitor the level and avoid buying cheap or counterfeit antifreeze.
Soil and dirt build-up in the radiator area gradually reduce heat dissipation. Modern cars often have multiple heat exchangers behind the grille, including automatic transmission radiators, power steering radiators, an air conditioning condenser, and the engine radiator farthest in the airflow path. A dirty radiator sandwich equals poor cooling. Regular cleaning is essential.
Engine oil plays a dual role: lubrication and cooling. In tough driving conditions, a low oil level can contribute to overheating. Regular checks and top-ups are important.
Immediately and unexpectedly
Steam bursts from under the hood can signal a sudden failure. In such cases, stop promptly and take the obvious steps—hose replacement and refilling the coolant—then arrange service. A slower but steady leak in the radiator tubes can produce a similar scenario.
The coolant pump or its drive can fail as well. Impeller blades may corrode or rotate on the shaft. Some vehicles use a clutch-driven pump, while others rely on electric designs. To test circulation, start a cold engine and feel the hoses to the heater: if both warm up gradually, coolant is circulating. If the supply hose stays cool while the return heats up, circulation is compromised.
An expansion tank connected to the cooling circuit shows droplets when the pump is operating, making diagnostics easier.
The notorious GM engine heat exchanger can allow oil and coolant to mix, or leak to the outside, hindering cooling performance.
The heat exchanger between coolant and oil located near the filter fitting is often more reliable than GM’s setup in some vehicles.
Broken cylinder head gasket means combustion gases can enter the cooling system and displace coolant, leading to rapid overheating. Stop the engine and seek service.
If the thermostat sticks closed, coolant cannot reach the radiator and the engine overheats quickly. A quick check on a cold engine is to feel the upper radiator hose after starting; if it does not get hot, the thermostat may be stuck.
A failed fan, whether belt-driven or electric, disrupts cooling. Modern designs use electric or viscous-coupled fans; testing may involve supplying voltage to the fan connector if the unit does not respond. When the fan fails, increasing heat with the heater turned on high can help manage cabin comfort but is not a fix for engine cooling.
A leaking radiator cap or expansion tank cap lowers the boiling point of the coolant and speeds overheating. Replacing a defective cap with the correct pressure rating is important.
Low-octane gasoline can trigger late ignition timing, raising the likelihood of overheating. If gasoline reliability is in doubt, refuel at a trusted brand and consider higher-octane options where appropriate. Persistent overheating is dangerous and typically indicates a major issue requiring an overhaul.
- Is the engine stuttering? Here’s what to check.
- For more on the topic, see additional content on this subject.