What is a Radiator Fan?
Pulls cool air through the radiator when the car isn't moving fast enough to do it on its own
Simplified animation — not to scale.
In plain English
The radiator fan is an electric (or, on older cars, belt-driven) fan mounted directly behind or in front of the radiator. Its job is to force air through the radiator core when there isn't enough natural airflow — typically when you're sat in traffic, crawling in a queue or idling on the drive. Most modern cars have one or two fans controlled by the engine's ECU based on coolant temperature and air-conditioning demand.
"Think of the radiator fan like the desk fan you switch on during a heatwave. When you're walking around outdoors there's plenty of breeze and you don't need it, but the moment you sit still at your desk, you flick the fan on to keep cool. Your engine works the same way — it gets free airflow when you're moving, but needs a fan to stay cool in traffic."
How it works
A temperature sensor in the cooling system constantly reports the coolant temperature to the ECU. Once the coolant climbs past a set threshold (often around 95–100°C), the ECU switches the fan on, sometimes at low speed first and then high speed if temperatures keep rising. The fan pulls a large volume of air through the radiator fins, which carries heat away from the coolant flowing through them. When you start moving at speed, ram air through the grille usually does the job on its own and the fan switches off. The fan will also kick in whenever the air conditioning is running, because the A/C condenser sits in front of the radiator and needs airflow too.
Signs of trouble
- ⚠Temperature gauge climbing in traffic but settling once you're moving
- ⚠Fan running constantly, even when the engine is cold
- ⚠Fan never audibly running, even after a long idle on a warm day
- ⚠Coolant warning light or overheating after sitting in a queue
- ⚠Air conditioning that blows warm at a standstill but cools when driving
- ⚠Loud rattling, buzzing or grinding from behind the grille
£140 to £500 fitted, more on premium or German cars
Always get a written quote. Prices vary by car, region, and parts brand.