Chapter 5 — Seasonal: winter and summer preparation

Seasonal car maintenance is often misunderstood as a reactive process rather than a preventative one. The mechanical stresses of a UK winter are fundamentally different from the thermal demands of a record-breaking summer. While modern vehicle engineering has extended service intervals, the environmental extremes of the British climate continue to account for the majority of non-collision roadside recoveries. Preparing for these shifts requires more than just checking fluid levels; it demands an understanding of how temperature affects chemical and structural stability within the vehicle’s core systems.

01The October Battery Health Test

Vehicle batteries are chemical storage devices that are significantly affected by ambient temperature. As the thermometer drops, the chemical reaction inside a lead-acid or AGM battery slows down, reducing its ability to provide cold cranking amps (CCA). Simultaneously, a cold engine requires more energy to turn over because the engine oil has thickened. October is the critical window for testing because it precedes the first sustained frosts that typically lead to battery failure.

• Check for physical signs of corrosion around the terminals, which increases electrical resistance.
• Ensure the battery is physically secure; vibration is a leading cause of internal plate damage.
• Measure the resting voltage with a multimeter. A healthy battery should read between 12.6V and 12.7V when the engine is off.
• If the reading is below 12.2V, the battery is at approximately 50% charge and may fail when the temperature drops below freezing.

If the vehicle has a 'smart' alternator or stop-start technology, it may require a professional diagnostic tool to assess the State of Health (SOH) rather than just a simple voltage check. Replacing a weak battery in the autumn is a far more cost-effective strategy than a call-out for a recovery service in January.

02Antifreeze and Cooling System Integrity

The terminology 'antifreeze' is somewhat reductive, as Modern Organic Acid Technology (OAT) coolants also act as corrosion inhibitors and lubricants for the water pump. In winter, the primary concern is the freezing point of the coolant. If the mixture is too diluted, the fluid can freeze and expand, potentially cracking the engine block or the radiator. Most manufacturers specify a 50/50 mix of concentrate and deionised water, which typically provides protection down to -35°C.

• Use a refractometer or a hydrometer to check the specific gravity of the coolant. This identifies the actual freezing point rather than just the volume.
• Never top up the system with plain tap water, as this introduces minerals that cause scale build-up and reduces the concentration of protective additives.
• Check the colour of the fluid. If the pink, blue, or green dye appears muddy or brown, it suggests internal corrosion or a failing head gasket, requiring an immediate flush and investigation.

03Summer Air Conditioning Maintenance

Air conditioning is often neglected during the winter months, leading to the drying out of internal seals. By the time summer arrives, the refrigerant gas (typically R134a or the newer R1234yf) may have leaked below the threshold required to trigger the compressor. A common misconception is that air conditioning is solely for cooling; however, it is the most effective tool for dehumidifying a cabin. If the system fails to clear a misted windscreen quickly, it likely needs a 're-gas' or a fresh cabin filter.

A professional air-con service should involve more than just a gas top-up. It should include a vacuum test to check for leaks and the addition of a specific UV dye to aid future fault-finding. Replacing the pollen filter annually is also essential; a blocked filter restricts airflow over the evaporator, reducing efficiency and potentially causing a stale odour in the cabin as bacteria build up in the moist environment.

04Essential Long-Journey Kit List

The requirements for a long-distance kit vary by season, but the core objective remains the same: self-sufficiency in the event of a breakdown or a major motorway closure. The National Highways agency frequently highlights that many motorway strandings are exacerbated by a lack of basic provisions. For any significant journey, the following should be considered mandatory.

• A high-visibility vest for every occupant, kept in the cabin rather than the boot.
• A physical road atlas, as GPS signals can fail in remote areas or during hardware malfunctions.
• In winter: A heavy blanket, a collapsible snow shovel, and a bag of grit or sand for traction.
• In summer: At least two litres of bottled water per person and a supply of any essential daily medication.
• A portable power bank for mobile phones, as a dead vehicle battery means the dashboard 12V sockets will not function.
• A UK-compliant first aid kit and a warning triangle (note that warning triangles should not be used on motorways for safety reasons).

05Tyre Considerations and Pressure Adjustments

Tyre pressures fluctuate with the seasons. As air cools in winter, it becomes denser, leading to a drop in PSI. Conversely, high summer road temperatures cause pressures to rise. Both scenarios affect the tyre's contact patch, impacting braking distances and fuel economy. During seasonal transitions, check pressures when the tyres are ‘cold’—usually after the car has been stationary for at least two hours. In the UK, while winter tyres are not a legal requirement, they offer significantly better grip when temperatures stay below 7°C. If staying on summer tyres, ensure the tread depth is well above the legal minimum of 1.6mm; 3mm is widely recommended for safe wet-weather performance.

Effective vehicle management requires an awareness of these cyclical needs. By addressing battery health in the autumn and cooling systems before the summer heat, a driver can significantly reduce the probability of mechanical failure. Prevention remains the most reliable method of ensuring both vehicle longevity and personal safety on the road.