UK motorists are being urged to act fast if they spot persistent white smoke coming from their vehicle's exhaust - especially on a warm day. According to motoring expert Matt Boesch from B2 Fabrication, a leading exhaust specialist, ignoring this key warning sign could result in engine damage costing well over £700.
While a small amount of vapour is perfectly normal on cold mornings, Boesch warns that thick white smoke in milder weather is often a red flag for a failing head gasket - a critical engine component that keeps combustion gases in and coolant out.
"If you notice thick white smoke even on a warm day, it could mean your engine is burning coolant," Boesch explains. "That's a strong indication your head gasket is in trouble. Keep driving like that and you're inviting severe, possibly irreversible, engine damage."

The expert's advice is crystal clear: pull over immediately and arrange for a tow to a mechanic, as continuing to drive could push the car beyond repair.
White smoke isn't the only giveaway. Drivers should also check for including milky-coloured oil, the engine overheating and a sudden loss of power
Each of these symptoms points to a potential head gasket failure, which will only get worse over time.
Boesch said: "A damaged head gasket won't heal itself. If anything, the longer you ignore it, the more expensive the repair becomes."
Some motorists may be tempted by quick-fix sealants available online or in auto shops. However, Boesch urges caution, explaining these are only ever temporary solutions.
"You might get a few weeks or months of extra use, but the issue will come back - and often worse than before," he said.
The cost of replacing a head gasket varies by vehicle, but drivers should expect to pay at least £700, with some repairs running significantly higher. Boesch recommends having a repair fund set aside for emergencies like this, as catching the issue early can often prevent more serious damage.

Beyond white smoke, Boesch also highlights the importance of noticing or nothing other changes. Blue smoke may signal oil burning due to worn piston rings or valve seals. Black smoke could indicate fuel system problems.
He said: "The exhaust is your car's way of talking to you. Change in colour, smell or volume of smoke is your cue to listen and investigate."
Dashboard warning lights are another early indicator of trouble. Many drivers ignore them, assuming the problem can wait. But Boesch warns these alerts are often the first sign of issues that can rapidly escalate.
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