Summer Driving Checklist: Keeping Cool in Traffic and Avoiding Overheating

The worst time to discover a cooling problem is stationary in a queue on a hot afternoon, watching the temperature gauge creep past halfway while the air conditioning blows something closer to warm breath. Breakdowns on hot days are rarely sudden. They build quietly over weeks — a coolant level dropping a centimetre at a time, a tyre running soft, a battery that has been cooked by months of under-bonnet heat. An hour spent checking a few things now is far cheaper than a recovery truck later.

Start With the Cooling System

Everything else on this list matters less than keeping the engine at the right temperature. Check the coolant level in the expansion tank when the engine is stone cold, not after a drive, and top up to the marked line with the correct pre-mixed coolant for your car. If you are adding a noticeable amount every few weeks, something is escaping — a hose, the radiator, the cap, or a head gasket — and it needs diagnosing rather than topping up forever.

Look at the coolant itself. Fresh coolant is usually bright and clear. Brown, rusty or oily coolant, or sludge around the filler neck, suggests it is long overdue a change. Your handbook gives the interval; most cars want it every few years, and plenty never get it.

While the engine is cold, squeeze the radiator hoses. They should feel firm and springy, not spongy, cracked or bulging near the clips. Run your hand along the radiator core if you can reach it, and check the fins are not packed with dead insects, leaves and grass seed. A gentle hose from the front, with the engine off, clears a surprising amount of blockage. Finally, listen for the cooling fan once the engine is warm — it should cut in when the temperature rises. A fan that never runs means a fuse, relay or sensor fault waiting to strand you.

Air Conditioning: Service It Before You Need It

Cabin air conditioning is not a luxury in a hot climate; it is what keeps you alert in stop-start traffic. Two things go wrong most often. The first is airflow: a clogged cabin filter leaves you with a weak, musty draught. They are cheap and usually behind the glovebox. The second is refrigerant loss through aged seals. If the system blows cool for ten minutes then fades to lukewarm, or never really gets cold, a specialist needs to leak-test it rather than simply refill it.

Run the air conditioning briefly every couple of weeks all year, including winter. Seals stay lubricated, the compressor keeps working, and you notice problems before a heatwave. On a hot day, open the windows for the first minute to dump the hottest air, set the system to recirculate, then switch back to fresh air once it has cooled. Park with a sunshade on the windscreen and the rear windows cracked an inch where it is safe to do so.

Tyres Carry More Heat Than Anything Else

Heat is the enemy of rubber. An underinflated tyre flexes more with every rotation, and that flexing generates heat that weakens the structure from the inside. Long motorway runs on a warm day are exactly the conditions that turn a slow puncture into a blowout.

Check pressures when the tyres are cold, using the figures on the driver's door pillar or fuel flap — not the maximum printed on the sidewall. If you are loading the car for a holiday, use the heavier-laden pressures listed in the handbook. Pressures rise as you drive, so never bleed air out of a hot tyre; that just leaves you underinflated when it cools.

• Tread depth: measure across the width and at several points around each tyre. In the UK the legal minimum is 1.6mm, but grip in standing water drops off long before that — 3mm is a sensible working floor.
• Damage: look for cuts, bulges and objects in the tread, and check the inner shoulders, which wear out of sight.
• Age: rubber hardens. A tyre older than about six years deserves a close inspection even with plenty of tread.
• The spare: if you carry one, check its pressure too. A spare at half pressure is barely better than no spare.

Fluids, Belts and the Battery

Engine oil does some of the cooling work, and a low level on a hot run strains everything. Check it cold, on level ground, and look at the colour as well as the level. Washer fluid matters more than people expect in summer, when windscreens collect insects and dust; keep the reservoir topped up with proper screen wash rather than plain water.

Batteries dislike heat more than cold. High under-bonnet temperatures accelerate internal corrosion, and a battery that has survived winter quietly gives up in July. Clean and grease the terminals if they look furry, and treat a slow, laboured crank as an early warning rather than something to ignore.

Carry Water, and Know What to Do With It

A few litres of water in the boot covers two very different emergencies: you, and the car. Keep drinking water for passengers, and a separate container for the cooling system. A basic summer kit is small and cheap:

• Two to four litres of drinking water per person on longer trips
• A litre or two of pre-mixed coolant, plus a funnel
• Hi-vis vest, warning triangle, torch and gloves
• Jump leads or a jump pack, and a tyre pressure gauge
• Sunshade, hats, and a phone charger or power bank

Never open a hot radiator or expansion cap — pressurised coolant can scald badly. And never leave children or pets in a parked car on a warm day, even briefly with the windows down. If you or a passenger starts to feel unwell in the heat, stop somewhere shaded and drink water; persistent symptoms need medical advice rather than more driving.

If the Gauge Starts Climbing

Act early. Warning signs include the temperature needle moving above its normal position, a warning light, steam from under the bonnet, or a sweet, syrupy smell.

1. Switch off the air conditioning and turn the heater to maximum heat with the blower on full. It is uncomfortable, but it pulls heat out of the engine.
2. Ease off the throttle and keep moving if traffic allows. Coasting with airflow through the radiator cools far better than idling.
3. If the needle keeps rising, pull over safely, switch off the engine and let it cool. Steam under the bonnet means stop now, not at the next services.
4. Wait at least twenty minutes before touching anything. Do not open the coolant cap while the system is pressurised.
5. Once cool, check the level and look for obvious leaks. Top up with pre-mixed coolant, or plain water as a short-term get-you-home measure, then have the system checked properly.
6. If it overheats again, stop driving. Head gaskets and warped cylinder heads cost far more than a recovery call.

The Twenty-Minute Check That Saves a Day

Do the checks cold, before a long trip or the first properly hot weekend of the year, and keep a note of when the coolant and air conditioning were last serviced. Tyre pressures take five minutes at a garage forecourt; the coolant and oil take another five; the rest is a walk around the car with your eyes open. That is the whole routine. Get it done on a mild morning and the hot queues stop being a gamble.

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