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Security & TechWhy Is My Car Overheating?
By Sun Garage, Owner, Sun Garage · 4 March 2026 · 6 min read
Why overheating is never worth ignoring
Your engine runs at a carefully controlled temperature, usually around 90°C. The cooling system — coolant, radiator, water pump, thermostat and fan — all work together to keep it there. When one part fails, temperatures can climb quickly, and modern engines have very little tolerance for running hot.
We see overheating cars come into our West Bromwich workshop every week, often from drivers who kept going for 'just a few more miles'. That decision is usually what turns a cheap fix into an expensive one.
The most common causes
Overheating almost always comes down to coolant not circulating properly, or not being there at all. The usual culprits are:
What typically causes an engine to overheat:
- Low coolant – from a slow leak in a hose, radiator or water pump seal
- A faulty thermostat – stuck closed, blocking coolant flow
- A failing water pump – no longer circulating coolant around the engine
- A blocked or damaged radiator – unable to shed heat effectively
- A broken cooling fan – especially noticeable in slow traffic or when stationary
- A blown head gasket – which can be a cause of overheating, or a result of it
Spotting the warning signs early
Most overheating problems give you some notice before things become serious. Knowing what to look for can save you a roadside breakdown.
The temperature gauge
Keep half an eye on it, especially on longer drives or in slow traffic. If the needle creeps towards the red zone, that's your earliest and clearest warning.
Steam or a sweet smell
Steam from under the bonnet, or a sweet smell inside the cabin, usually means coolant is leaking or boiling. Don't dismiss this as 'just the heater'.
Warning lights
A red temperature warning light means stop as soon as it's safe — this is different to the normal blue 'engine warming up' light, which simply means the engine hasn't reached operating temperature yet.
What to do if your car starts overheating
How you react in the first few minutes makes a real difference to how much damage occurs — and how much the repair costs.
If your temperature gauge is in the red, pull over safely and turn off the engine as soon as you can. Do not open the radiator cap or coolant reservoir while the engine is hot — pressurised, near-boiling coolant can cause serious burns. Wait at least 30 minutes before checking coolant levels.
Why overheating leads to head gasket failure
The head gasket seals the join between the engine block and cylinder head, keeping coolant, oil and combustion gases separate. Excessive heat causes the metal components either side to expand unevenly, and the gasket simply can't cope — it can blow, allowing coolant and combustion gases to mix.
Once that happens, you may see white smoke from the exhaust, a mayonnaise-like residue under the oil cap, or coolant disappearing with no visible external leak. This is a significant repair, but continuing to drive on a failed head gasket risks warping the cylinder head entirely, turning a repair into a full engine rebuild.
How we diagnose and fix overheating in West Bromwich
When you bring an overheating car to us, we start with a proper diagnosis rather than guessing — pressure-testing the cooling system, checking the thermostat and water pump, and inspecting for head gasket failure using a chemical block test and visual checks.
Whether it's a simple thermostat replacement or a full head gasket repair, we'll explain exactly what's gone wrong and give you a clear, honest quote before any work starts. Call us on 0121 553 0296 if your car has started running hot.