Few things are more alarming than watching your temperature gauge climb into the red. Engine overheating can cause catastrophic damage – and often indicates a fault that existed when you bought the car. Here's what to do if your recently purchased car overheats.
Why Overheating Is So Serious
Overheating can cause head gasket failure (an £800-£2,500 repair), a warped cylinder head that often requires engine replacement, a cracked engine block that may write the car off entirely, or a seized engine – complete failure. A single serious overheating event can destroy an engine. That's why cooling system faults are taken so seriously.
Common Cooling System Problems
Head Gasket Failure
The head gasket seals the cylinder head to the engine block. Failure allows coolant and oil to mix, or coolant to leak into cylinders.
Symptoms include overheating, white smoke from the exhaust, a milky residue under the oil cap, coolant loss with no visible leak, bubbling in the coolant reservoir, and a sweet smell from the exhaust.
Coolant Leaks
Leaks anywhere in the system cause coolant loss and overheating.
Common leak points include the radiator (cracks or corrosion), hoses (splits or loose clamps), water pump (seal failure), heater matrix (causing a leak inside the cabin), head gasket (internal leak with no visible drip), and the expansion tank itself (cracks from age or pressure).
Water Pump Failure
The water pump circulates coolant. When it fails, coolant doesn't flow.
Signs include overheating, a whining noise from the pump area, coolant leaking from the pump weep hole, steam from the engine bay, and a wobbling pulley.
Thermostat Problems
The thermostat controls coolant flow. Failure causes overheating or overcooling.
When the thermostat gets stuck closed, coolant can't flow to the radiator and the engine overheats rapidly. When it gets stuck open, the engine runs too cool, leading to poor fuel economy and a heater that doesn't work properly.
Radiator Blockage
Blocked radiators can't dissipate heat.
Blockages can be caused by internal debris and corrosion, external blockage from leaves and insects, damaged fins, or stop-leak products clogging the system – the last one is particularly telling if a dealer has been trying to mask a leak.
Cooling Fan Failure
Electric fans cool the radiator when stationary or slow. Failure causes overheating in traffic.
The telltale sign is a car that overheats in traffic but runs fine on the motorway, because airflow through the radiator compensates for the broken fan at speed. Other signs include the fan not running when the engine is hot, the fan running constantly, or the AC stopping because some cars share a fan between the radiator and condenser.
EGR Cooler Failure
Diesel cars have EGR coolers that can fail and cause overheating or coolant loss.
Symptoms include coolant loss, white smoke, rough running, and a check engine light.
Did the Dealer Know?
Cooling system faults often show warning signs dealers can spot – or hide:
Fresh coolant that's been recently topped up can hide a leak. A new expansion tank cap covers evidence of pressure issues. Radiator stop-leak added to the system is a temporary fix for leaks that will fail again. A recent coolant flush removes evidence of contamination, and a cleaned engine bay hides leak stains. These are all red flags that a dealer was masking a known problem.
Before selling, a responsible dealer should check coolant level and condition, signs of head gasket failure, visible leaks, fan operation, and temperature gauge behaviour. If they didn't check these things, that's their negligence – not your problem.
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Is It a Fault?
Head gasket failure is a major mechanical defect. Coolant leaks are active system failures. Water pump failure is a component failure. Overheating within days or weeks of purchase points clearly to a pre-existing problem. Any cooling system warning lights indicate a system malfunction. All of these are definitively faults under the Consumer Rights Act.
The Pre-Existing Test
Cooling systems don't fail suddenly. If your car overheats within weeks of purchase, the head gasket was already weakened, the leak already existed (even if it was small), the pump was already failing, or the thermostat was already stuck. You haven't caused these problems in a few weeks of normal driving.
Head Gasket Special Case
Head gasket failure is particularly telling because gaskets don't fail overnight – the failure develops over time, and previous overheating accelerates it. If your head gasket fails shortly after purchase, it's highly likely the car had already overheated before you bought it.
Your Legal Rights
Consumer Rights Act 2015
An overheating car isn't of satisfactory quality because it must be able to run without overheating, isn't fit for purpose because it can't be used as reliable transport, and isn't as described unless cooling faults were specifically disclosed at the point of sale.
30-Day Right to Reject
Within 30 days, reject for a full refund. Overheating is a clear fault – no dealer can argue otherwise.
After 30 Days
Request repair. If it fails or causes further problems, you can reject.
Warning: Head gasket repairs often fail or reveal further damage. Don't accept a "fixed" car without guarantees.
If the Engine Is Destroyed
If overheating has destroyed the engine, the car clearly isn't of satisfactory quality. Reject for a full refund – don't accept partial repairs to a damaged engine.
Repair Costs
| Problem | Parts | Labour | Total |
|---|---|---|---|
| Thermostat | £20-£60 | £50-£150 | £70-£210 |
| Water pump | £50-£200 | £100-£300 | £150-£500 |
| Radiator | £100-£400 | £100-£200 | £200-£600 |
| Cooling fan | £80-£250 | £50-£150 | £130-£400 |
| Head gasket | £100-£300 | £500-£1,500 | £600-£1,800 |
| Head gasket + head skim | £150-£400 | £800-£2,000 | £950-£2,400 |
| Engine replacement | £1,500-£5,000 | £500-£1,500 | £2,000-£6,500 |
Cooling system repairs range from minor to catastrophic. Don't pay these costs if the fault existed at sale.
Recommended reading
What to Do When Your Car Overheats
Step 1: Stop Immediately
If the temperature gauge goes into the red, pull over safely and turn off the engine immediately. Do NOT open the bonnet straight away – there's a serious burn risk from pressurised steam. Wait for it to cool down. Never keep driving an overheating car. The damage increases rapidly with every minute.
Step 2: Document Everything
Take a photo of the temperature gauge, note the mileage, record when it happened and what warning lights appeared, and video any steam or smoke. This evidence will be crucial if you need to reject the car.
Step 3: Don't Drive It Home
If the car has seriously overheated, call for recovery rather than restarting and hoping for the best. Further driving could destroy the engine entirely. Keep your recovery receipts – you can claim these costs back from the dealer as they're a direct consequence of the fault.
Step 4: Get a Diagnosis
Take it to an independent garage for a cooling system pressure test, head gasket test (sniff test or block test), thermostat function check, and water pump inspection. Get a written diagnosis – you'll need this for your rejection claim.
Step 5: Contact the Dealer
Write formally to the dealer describing what happened, stating that the fault was pre-existing, including your mileage since purchase to show how little you've driven it, and demanding either rejection or repair. Set a clear deadline for their response – 14 days is standard.
Common Dealer Excuses
"You must have ignored the warning"
Your response:
"I stopped immediately when I noticed the temperature rise. The fault causing the overheating existed before I bought the car."
"Cooling systems do fail eventually"
Your response:
"Not within [X] weeks of purchase. This failure was imminent when you sold the car. The system was already compromised."
"You didn't maintain the coolant"
Your response:
"I've had the car [X] weeks. Coolant doesn't need topping up that frequently in a healthy system. The leak/failure existed at sale."
"We'll repair the head gasket"
Your response:
"I'm concerned that head gasket failure may have caused further engine damage. I'd like an independent assessment before deciding whether to accept repair or reject."
"It's not worth fixing – we'll refund part of the price"
Your response:
"If it's not worth fixing, I'm entitled to a full refund, not a partial one. I bought a car, not a write-off."
When to Reject vs. Accept Repair
Consider rejection if you're within 30 days (your automatic right), if the head gasket has failed (repairs are often unsuccessful), if the engine has been seriously damaged, if the car has overheated multiple times, if you've lost confidence in the car, or if the repair cost exceeds the car's value.
Consider accepting repair if it's a minor issue like a thermostat or small leak, if you're past 30 days with no better option, if the repair is guaranteed in writing, or if you genuinely want to keep the car.
If you accept repair and it fails, you can still reject later. But always get any repair guarantee in writing.
Head Gasket Specific Advice
Head gasket failure deserves special attention:
The Damage May Be Worse
Head gasket failure often causes a warped cylinder head (needing skimming), a cracked head (needing replacement), engine damage from oil and coolant contamination, and turbo damage on turbocharged cars. What starts as a "head gasket repair" may reveal that the engine is scrap.
"Repaired" Head Gaskets
Dealers sometimes sell cars with recently repaired head gaskets. If it fails again, the repair was inadequate, the underlying damage was missed, and you're entitled to reject. A recently repaired head gasket that fails shortly after you buy the car is strong evidence the dealer knew about – and tried to patch – the problem.
Head Gasket Sealers
Some dealers use liquid sealers as a temporary fix. These don't last. If your head gasket fails after the dealer "fixed" it with sealer, the fix was inadequate.
The Bottom Line
Engine overheating is serious. It can destroy your engine and leave you with a worthless car.
If your car overheats shortly after purchase, the cooling system fault almost certainly existed at sale – you haven't caused it in a few weeks of normal driving. You're entitled to rejection or repair, and you shouldn't pay thousands for the dealer's problem. Act quickly, document everything, and don't accept excuses. If you bought on finance, the finance company is jointly liable – write to them at the same time as the dealer. A car that overheats isn't of satisfactory quality, full stop.
Car overheated after purchase? Check if you qualify for a rejection before more damage is done.
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