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Diagnostics & EmissionsCar Overheating — What To Do, Common Causes, and When To Stop Driving
27 July 2026 · 5 min read
Stop immediately — why driving an overheating car is dangerous
If your temperature gauge climbs into the red or a coolant warning light illuminates, pull over safely and switch off the engine as soon as it is safe to do so. Do not try to limp the car to a garage. Continuing to drive an overheating engine for even a short distance can warp or crack the cylinder head, damage head gasket seals, score the cylinder walls, or seize the engine entirely — turning what might have been a £300 thermostat replacement into a £2,000-plus head gasket repair or an engine that cannot be saved.
Once stopped, leave the engine to cool for at least 20 to 30 minutes before opening the bonnet. Never open the coolant cap on a hot engine — the system is pressurised and hot coolant can spray and cause serious burns. When cool, check the coolant level in the expansion tank. If it is low, there is a leak somewhere in the system. Call us on 07498 392333 and describe what happened — that information alone helps us narrow down the likely cause before you arrive.
Most common causes of engine overheating
The most frequent cause we see at Urban Autohaus is a failed thermostat — the valve that regulates coolant flow between the engine and the radiator. A thermostat stuck closed prevents coolant circulating at all, causing temperature to climb rapidly within minutes of starting from cold. A thermostat stuck open is less dramatic but prevents the engine reaching normal operating temperature, which increases wear and reduces fuel efficiency.
Other common causes include a failed water pump (either the impeller has corroded or the bearing has collapsed), a split or perished coolant hose that is leaking under pressure, a radiator that is blocked or has a leak at a seam or end tank, a cooling fan that is not operating correctly (particularly relevant when the car overheats in slow traffic but is fine at speed), or a blown head gasket that allows combustion gases to enter the cooling system and push coolant out.
Why your car might overheat even with a full coolant level
This is one of the most common questions we get: the coolant level looks fine but the temperature gauge is climbing. The most frequent explanation is a thermostat that is stuck closed — coolant level is fine but none of it is flowing. Another common cause is a faulty coolant temperature sensor sending incorrect data to the engine management system and temperature gauge, which can trigger the warning light even if the engine is not actually overheating.
A more serious cause is a head gasket that is leaking internally — combustion gases enter the coolant circuit, create an air lock, and prevent proper circulation even though the coolant reservoir appears full. You may also notice a sweet smell from the exhaust, white smoke from the exhaust when warm, or milky contamination under the oil filler cap. These symptoms together point strongly to a head gasket issue and require investigation before the engine is run further.
How we diagnose cooling system faults at Urban Autohaus
We start with a visual inspection and a cooling system pressure test to identify external leaks, followed by a diagnostic scan to check the coolant temperature sensor reading against actual engine temperature. If the external system appears sound, we carry out a combustion gas test on the coolant to rule out head gasket leakage into the cooling circuit — this is a chemical test that detects exhaust gases in the coolant, giving a fast answer on whether a head gasket failure is involved before any strip-down work is agreed.
We always give you a clear explanation of findings and a costed recommendation before any work begins. Cooling system faults range from a straightforward thermostat or hose replacement to more involved head gasket or water pump work — but diagnosing properly first means you only pay for what your car actually needs. Call us on 07498 392333 or book online. We are at Cornwallis Road, West Bromwich, B70 9BY and serve drivers from Sandwell, Birmingham, Dudley, Wolverhampton, and the wider West Midlands.