What causes a car to overheat?

The most common causes are low coolant (often from a leak), a faulty thermostat stuck closed, a failed water pump, a broken cooling fan, or a blocked radiator. In summer, heavy traffic and hot weather add load to a cooling system that may already be marginal, so a hidden weakness shows up as overheating.

What should I do if my car starts overheating while driving?

Turn off the air conditioning and turn the heater to full hot (it draws heat away from the engine), then pull over safely as soon as you can and switch off the engine. Do not open the bonnet immediately or remove the coolant cap while hot — you risk a serious scald from pressurised steam. Let it cool for at least 30 minutes before checking coolant.

Can I keep driving if my car is overheating?

No. Continuing to drive an overheating engine can cause severe, expensive damage — a warped cylinder head or blown head gasket, which can run into four figures. The moment the gauge climbs into the red or a warning light shows, treat it as urgent and stop as soon as it's safe.

How do I check my coolant level?

With the engine cold, find the coolant expansion tank under the bonnet (a translucent plastic reservoir with min and max marks). The level should sit between the marks. If it's low, top up with the correct coolant/antifreeze mix — but if it keeps dropping, you have a leak that needs fixing rather than just topping up.

How can I prevent my car overheating in summer?

Keep coolant topped up and at the right concentration, have the cooling system checked if the car is older, and watch the temperature gauge in heavy traffic. A car that runs hot in stop-start traffic but cools on the move often has a failing fan or low coolant — get it looked at before it leaves you stranded.

Why Is My Car Overheating? Summer Causes and What to Do

A temperature gauge creeping towards the red — especially in summer traffic — is one warning you genuinely can't drive through. Overheating can turn a cheap fix into a four-figure engine bill in minutes. Here's why it happens, exactly what to do in the moment, and how to stop it.

Why cars overheat

Your engine makes a lot of heat, and the cooling system's whole job is to carry it away. When something in that system fails, the heat builds. The usual suspects:

Low coolant — usually from a leak; the most common cause
A stuck thermostat — jammed closed, so coolant can't circulate
A failed water pump — no longer moving coolant through the engine
A broken cooling fan — so the car runs hot in traffic but cools on the move
A blocked or clogged radiator — reducing how much heat it can shed

Summer doesn't cause these on its own — but hot weather and heavy, stop-start traffic pile extra load onto the cooling system, so any hidden weakness shows up exactly when you least want it to.

What to do the moment it happens

If the gauge climbs into the red or a temperature warning light appears while you're driving, act fast and calmly:

Turn off the air conditioning — it adds load to the engine.
Turn the heater to full hot and the fan up. Counter-intuitive, but it pulls heat away from the engine and can buy you time.
Pull over safely as soon as you can and switch off the engine.
Do not open the bonnet straight away, and never remove the coolant cap while hot — the system is pressurised and can spray scalding steam. Wait at least 30 minutes to cool.
Once cool, check the coolant level and top up if low.

If it overheats again quickly, don't push on — call for help. A short tow is far cheaper than a new engine.

Why you can't just keep going

This is the part that costs people thousands. Driving on an overheating engine can warp the cylinder head or blow the head gasket — repairs that often run well into four figures. The engine doesn't give you much warning between "running hot" and "serious damage," so the gauge in the red is a stop-now signal, not a "make it home" one.

Checking your coolant

With the engine cold, find the coolant expansion tank — a translucent plastic reservoir under the bonnet with min and max marks. The level should sit between them. If it's low, top up with the correct coolant/antifreeze mix for your car.

But here's the key: if you keep having to top it up, you have a leak, not just a low level. Topping up masks the problem; finding and fixing the leak solves it.

Preventing it

Keep coolant topped up and at the right concentration year-round.
Have the cooling system checked if your car is older or you've noticed it running warm.
Watch the gauge in traffic — a car that heats up at a standstill but cools when moving often has a failing fan, an easy fix if caught early.

A summer service that includes a coolant and cooling-system check is cheap insurance against a roadside breakdown in 30-degree heat.

The bottom line

Overheating is one of the few faults where your reaction in the first 60 seconds decides whether it's a £60 fix or a £1,500 one. Stop as soon as it's safe, never open a hot system, and treat repeated top-ups as a leak to fix — not a habit. If your car's due a service or MOT, it's the perfect moment to get the cooling system checked; you can see when your MOT is due free with the registration and book it all in together.