Why Cars Overheat in Summer and When to Call a Tow

Updated Jul 2026 · 6 min read

Summer heat is hard on your cooling system

Hot weather asks a lot of the part of your car that keeps the engine from cooking itself. Your cooling system has to shed engine heat into air that is already warm, and when you add stop-and-go traffic, a loaded trunk, or a long climb up a grade, the margin gets thin. That is why breakdown calls for overheating tend to cluster in the hottest stretch of the year.

Knowing what an overheating engine looks like, what you can safely do about it on the shoulder, and the point where driving on becomes a bad idea can save you an expensive repair. Here is how to read the situation and decide when it is time to stop and get a tow.

What actually makes an engine overheat

An engine runs hot for one basic reason: heat is going in faster than the cooling system can carry it away. Several common problems lead there.

• Low coolant. A slow leak from a hose, the radiator, or the water pump lowers the fluid that moves heat out of the engine. Summer just exposes a weakness that was already building.
• A failing thermostat. If the thermostat sticks shut, coolant stops circulating to the radiator and temperatures climb fast, even on a short drive.
• A tired water pump. The pump pushes coolant through the system. When it wears out or its belt slips, flow drops.
• A clogged or blocked radiator. Bugs, road grime, or interior corrosion keep the radiator from doing its job.
• A broken cooling fan. In slow traffic the fan does most of the work. If it quits, the gauge often creeps up the moment you stop moving.

You do not need to diagnose which one it is from the driver's seat. You just need to recognize that the engine is telling you to stop.

Warning signs you should not drive through

Cars usually give you notice before things get serious. Watch for these:

• The temperature gauge climbing toward the red zone, or a hot-engine warning light coming on.
• Steam or vapor rising from under the hood.
• A sweet, syrupy smell, which often points to coolant escaping.
• Weaker power or a rougher idle as the engine protects itself.
• A ticking or knocking noise that was not there before.

Any one of these is a reason to slow down and find a safe place to pull over. Two or more together, especially steam, mean the engine is already past comfortable and every extra mile risks real damage.

What to do the moment it happens

If you spot the signs while driving, act calmly and get off the road.

1. Turn off the air conditioning and turn the heater on full. It feels backward on a hot day, but the heater pulls warmth out of the engine and buys you a little room to reach a safe spot.
2. Ease off the accelerator and find a place to stop. Coasting produces less heat than climbing or accelerating. A flat pull-off or a nearby lot is better than a narrow shoulder if you can reach one safely.
3. Shut the engine off once you are stopped. Leaving it running while it is overheating keeps adding heat with no benefit.
4. Pop the hood, but do not open it right away. Let the trapped heat vent before you get your hands near it.

The single most important safety rule: leave the radiator cap and coolant reservoir alone while the engine is hot. A pressurized cooling system can spray scalding fluid the instant you crack it open. Wait until everything has cooled fully before you even think about checking levels, and if you are unsure, do not touch it at all.

When adding coolant helps, and when it does not

Once the engine has cooled all the way down, topping up low coolant can sometimes get you moving again. Plain water works as a short-term fill if that is all you have. But treat a refill as a test, not a fix. If the level was low because of a leak, it will drop again, often quickly.

Adding fluid does nothing for a stuck thermostat, a dead fan, or a failed water pump. If the gauge climbs right back up after you refill and get going, that is your answer. Keep driving and you risk a warped cylinder head or a blown head gasket, which turns a roadside annoyance into a major repair.

When it is time to call for a tow

Some situations are not worth gambling on. Call for a tow rather than driving on if any of these apply:

• The gauge returns to the red soon after you refill and set off again.
• You see or smell coolant leaking under the car.
• Steam keeps coming from under the hood after the engine has had time to cool.
• The engine sounds different, runs rough, or loses noticeable power.
• You cannot safely check anything, or you simply are not sure what is wrong.

A flatbed keeps all four wheels off the road, which is the safest way to move a car whose engine or drivetrain may already be compromised. When you call, tell the dispatcher that the vehicle overheated and whether it is drivable, so they send the right truck. Many providers listed in this directory are available around the clock, which matters when a breakdown happens far from home or late in the day.

A little prevention goes a long way

Most summer overheating traces back to something that could have been caught earlier. Before the hottest weeks arrive, have a shop check the coolant condition and level, look over the hoses and belts for cracks or softness, and confirm the cooling fan kicks on as it should. If your car has a history of running warm, keep an eye on the gauge on long drives and in heavy traffic, and carry drinking water and a phone charger so a roadside wait is at least a comfortable one.

Overheating rarely comes out of nowhere. Read the signs early, stop before the damage compounds, and when the car is telling you it cannot go further, let a tow truck finish the trip.