The heatwave mistake Portsmouth drivers are about to make
As the UK Health Security Agency extends red heat health alerts across the South West, South East, London, East of England, West Midlands and East Midlands through to 11pm on Friday 26 June, drivers in Portsmouth will still head outside to wash their cars. It is, after all, the obvious thing to do in sunny weather.
But according to cleaning experts, washing your car during a heatwave is one of the most reliable ways to cause serious long-term damage to your paintwork.
This week has already broken records. Wednesday became the UK's hottest ever June day on record, with a provisional temperature of 36.1 degrees Celsius recorded in Gosport, Hampshire, surpassing the previous record of 35.6 degrees set in 1976. It is the first time in the history of the current warnings system that red extreme heat warnings have been issued for three consecutive days in the UK. Temperatures on Thursday could push further still, with 38 degrees likely and 40 degrees not entirely ruled out. It follows a May that also broke UK temperature records, making this the first time since 1911 that two consecutive months have seen record-breaking temperatures. For the nation's drivers, the instinct is to reach for the hosepipe. The problem is that in conditions like these, that instinct is actively working against them.
Why Hot Weather and Car Washing Do Not Mix
The issue is timing. Between 11am and 3pm during a heatwave, UV levels and surface temperatures peak and car panels become hot to the touch. At that temperature, soap and water applied to the surface begin to evaporate almost immediately, before they can be properly rinsed away. The result is soap residue, water spots and mineral deposits that dry directly onto the lacquer and can etch into it over time.
"Most drivers think a sunny day is the ideal time for a car wash," says Filipa Silva, cleaning expert at Nilfisk. "But washing in direct midday sun is one of the most damaging things you can do to your paintwork. The water and soap dry faster than you can rinse them off, and anything left behind bakes into the surface. The damage is gradual and cumulative, and by the time most people notice it, it is already expensive to fix."
The Cost of Getting it Wrong
The financial stakes are significant. Car paint repairs in the UK currently cost between £60 and £1,200 depending on the extent of the damage. A single panel respray sits between £363 and £669, while a full vehicle respray ranges from £900 to £1,600, with a quality finish costing considerably more. Heat-related wash damage, unlike stone chips or kerb scrapes, tends to be invisible until it has spread across multiple panels, at which point the repair bill escalates quickly.
When You Should Wash Your Car in a Heatwave
The fix is straightforward. Car care experts consistently recommend washing before 10am or after 5pm during hot weather, when surface temperatures have dropped and UV intensity is lower. If possible, wash in the shade rather than in direct sunlight, even during cooler parts of the day. The most important factor is timing, but speed matters too. The faster you can rinse soap and water off hot panels, the less chance there is of residue drying into the surface. A high-pressure washer rinses more quickly than a bucket and sponge, making it better suited to warm-weather washing than a slow hosepipe or bucket.
A Pattern Set to Continue
Wednesday's record was the latest in a series of broken benchmarks. The Met Office has confirmed this is the first time since 1911 that the UK has seen back-to-back months of record-breaking temperatures, and climate change is increasing both the frequency and intensity of UK heatwaves. With amber warnings already extending into Saturday across parts of the South East and East of England, the heat is not finished yet.
The best car wash you can do this summer is one you do early in the morning, in the shade, before the temperature climbs. Everything else is making a costly mistake in slow motion.