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The engine cooling system in your vehicle ensures that the engine runs at optimum operating temperature neither too high nor too low to avoid wear and tear of the engine components and to reduce fuel consumption. The radiator fan plays an important role in maintaining optimum engine temperature by facilitating heat exchange between the atmospheric air sucked in by the radiator fan and the coolant which takes away heat from the engine by circulating through the engine jacket. Ideally, the radiator fan gets switched ON only when the coolant reaches a certain threshold temperature level and the radiator fan gets switched OFF once the coolant temperature drops down below the threshold limit. But if there is any malfunction in the cooling system then the radiator fan could keep on running continuously irrespective of operating conditions. There are many probable reasons for triggering the issue of Ford F150 radiator fan runs constantly, but the most common reasons are defective radiator fan, bad radiator fan relay, leaky radiator hoses, low coolant levels, a faulty thermostat, malfunctioning water pump, bad coolant temperature sensor, clogged AC expansion valve, AC system leak, malfunctioning AC high-pressure sensor, bad AC compressor, undercharged AC refrigerant or it could be as simple as damaged system wiring harness. Does your Ford F150 radiator fan runs constantly? Are you looking for troubleshooting solutions to get rid of this problem? You are at the right place! Stay tuned! How Does Engine Cooling System Work? The engine cooling system of the vehicle comprises several parts like a radiator, condenser, water pump, coolant temperature sensor, radiator fan switch, thermostat, engine cooling jacket, connecting hoses, radiator cap, coolant reservoir, AC system parts (including AC high-pressure sensor, compressor, and AC expansion valve). Typically, a water pump circulates the coolant across the cooling system circuit and the coolant gets circulated through the engine cooling jacket from where the heat is transferred from the engine to the coolant. The engine is connected to the radiator's top portion by connecting hoses. The hot coolant via. hose enters the radiator where it exchanges the heat with the surrounding air pulled across the radiator fins by the radiator fan. The relatively cold coolant exits the radiator at the bottom portion and again enters the engine jacket. To ensure that the engine always runs at optimum operating temperature, the cooling circuit is divided into 2 circuits, short and long circuits. This is done with the help of a thermostat. The thermostat is normally closed and does not allow the coolant from the radiator to pass through the engine jacket. The short circuit bypasses the radiator to ensure that the engine is heated up quickly to achieve its normal operating temperature within no time. Once the engine temperature exceeds 82 degrees F, the thermostat partially gets opened up and allows the cold coolant from the radiator to pass through the engine jacket. Once the temperature exceeds 93 degrees F, the thermostat gets fully opened and completely allows the radiator coolant and closes the direct entry of coolant from the engine exit to the inlet point for faster cooling of coolant. The coolant temperature sensor is typically mounted at the exit of the engine jacket and it senses the coolant temperature and gives input to the ECM (Engine Control Module) for switching the radiator fan ON or OFF depending upon the coolant temperature. This is to control the duty cycle of the radiator fan, otherwise, it would unnecessarily run continuously affecting the fan's durability life and draining the battery as well. Hence the radiator fan is preferred to run intermittently to improve overall vehicle operating efficiency. Does Your Ford F150 Radiator Fan Runs Constantly? 12 Probable Reasons And Solutions To Fix It! A malfunction in any one of the cooling system parts would affect the engine cooling performance and result in improper operation of the radiator fan. If your radiator fan runs constantly, then below are the probable reasons and the solutions to fix it. Defective fan The radiator fan is supposed to suck the air effectively across the radiator fins for cooling the coolant. But when the radiator fan is defective or broken and it is especially making a lot of noise, then chances are that there won’t be effective cooling of coolant, hence the coolant temperature sensor continuously sends high-temperature signals to ECM which thereby keeps the Ford F150 radiator fan run constantly. You need to check the condition of the radiator fan, inspect and identify the defects, and replace the radiator fan with a new one if required. Bad radiator fan relay The ECM communicates the radiator fan through the radiator fan relay. It may happen that the coolant temperature sensor may be sending correct and low coolant temperature signals to the ECM when the vehicle has just started but if the fan relay is faulty and the switch contacts are closed continuously then the radiator fan would run constantly irrespective of actual coolant temperature. The Ford F150 radiator fan would stay on unless the faulty radiator fan relay is replaced with a new one. Leaky radiator hoses The radiator connecting hoses need to be inspected periodically and to be checked for any leakage. The radiator hose sometimes gets damaged and leaks the coolant thereby reducing the coolant levels in the cooling circuit. Once the coolant level gets reduced below some threshold limit, the amount of coolant won’t be sufficient to take away the heat effectively from the engine hence the coolant temperature remains high all the time, hence the Ford F150 radiator fan runs constantly irrespective of coolant operating temperature. Thoroughly inspect all connecting hoses which connect the engine to the cooling system and replace the leaky hoses Low coolant levels If you are residing in high ambient temperature, then it would put a load on the cooling system and increase the coolant consumption. If you are not topping up the coolant, then the low coolant levels will have the same effect as leaky coolant hoses and increase the coolant temperature which further ensures that the radiator fan in your Ford F150 runs constantly. Check for the coolant levels periodically and top up if required to ensure that the coolant level is not creating any issues. Faulty Thermostat A faulty thermostat could make your Ford F150 radiator fan run constantly. This is because the thermostat which has to be opened fully when the coolant temperature exceeds 93 degrees F won’t open at all if the thermostat has gone bad. The faulty thermostat is typically stuck partially or fully closed and won’t allow or reduce the cold coolant flow from the radiator which thereby increases the coolant temperature drastically and makes the Ford F150 radiator run constantly to reduce the coolant temperature. You would need to replace the faulty thermostat with a new one to get rid of this problem. You may also try reducing the thermostat rating from 190 to 160 degrees F and see and see whether the Ford F150 radiator fan stops running constantly. If the ECM is not calibrated properly with the coolant temperature sensor, then the coolant temperature sensor will always be reading higher than the actual engine temperature (at which the thermostat opens up) which would make the ECM run the radiator fan constantly. Now the radiator fans will never come on unless there is an actual issue with the radiator temperature. Malfunctioning water pump The water pump circulates the coolant across the system, if it goes bad then it won’t maintain the coolant flow rate across the engine. Any reduction in coolant discharge will shoot up the coolant temperature to a level that would trigger the radiator fan to run constantly regardless of the actual coolant temperature. You may need to replace the water pump with a fresh one from auto shops and confirm for fixing the radiator fan constantly running issue. Bad coolant temperature sensor The coolant temperature sensor (CTS) sends temperature input signals to the ECM, if it goes bad then it would be erratically sending random inputs to the ECM which would make the radiator fan run constantly in your Ford F150. In some old vehicles, instead of CTS, a radiator fan switch is used to switch the radiator fan ON and OFF. If the radiator fan switch goes bad, it would have the same effect as a bad CTS. Inspect and calibrate the coolant temperature sensor or radiator fan switch and replace CTS with a new one if required. Clogged AC expansion valve The AC expansion valve reduces the pressure drastically from high to low pressure to reduce the refrigerant temperature to pick up heat from the evaporator. But if the AC expansion valve gets clogged or fails then instead of pressure reduction, the refrigerant pressure would keep on increasing on the high side towards the condenser side and the refrigerant temperature would also increase accordingly. High refrigerant temperature would cause the ECM to think that the engine would be running too warm and it turns the condenser cooling fans ON to reduce the refrigerant temperature and pressure. Unless the faulty AC expansion valve is replaced with a new one, your Ford F150 radiator would run constantly. AC system Leak Any refrigerant leak in the AC system would undercharge the refrigerant to such an extent that would force the ECM to keep the condenser radiator fan to run constantly in your Ford F150. You need to inspect the refrigerant lines and check for leakage if any. People often report that the AC compressor leaks green fluid. Apart from the compressor, your problem may lie at any of the refrigerant pipe joineries Bad AC high-pressure sensor The AC high-pressure sensor is the one that senses the refrigerant pressure on the high side between the compressor and expansion valve and gives input to ECM for switching the condenser radiator fan ON or OFF. If the AC high-pressure sensor goes bad, then the ECM would read the pressure incorrectly and that would make the ECM think that the pressure on the high-pressure side is too high and that would keep the Ford F150 radiator fan running continuously If the A/C is working well, then the pressure sensor has gone bad and needs to be replaced. Malfunctioning AC compressor The AC compressor is supposed to switch ON and OFF based on refrigerant pressure input. If the AC compressor goes bad, then it won’t receive signals from the ECM and runs continuously. Continuous compressor running would mean increased refrigerant pressure on high pressure side and will keep your radiator fan running constantly in your Ford F150. Inspect the part and replace AC compressor with a new one, if found faulty. Damaged wiring harness The wiring harness which is connected to the engine to measure cylinder head temperature (CHT) shall be checked for any damage. A small voltage drop due to damage would cause a large increase in temperature that the ECM would read. If the ECM reads higher temperature which is not, then it would keep the radiator fan running constantly to reduce the coolant temperature which may be lower. Conclusion The radiator plays a vital role in maintaining the engine operating temperature. If you take any component of the vehicle, it has got limited durability life. Here we have tried to collate the probable reasons that may cause your Ford F150 radiator fan to run constantly. You may need to troubleshoot the cooling system by checking each part thoroughly to pinpoint the root cause of the problem in your vehicle. Happy Motoring! References https://www.f150forum.com/f118/engine-cooling-fans-running-high-speed-489652/ https://www.cargurus.com/Cars/Discussion-t43203_ds857422 https://www.ifixit.com/Answers/View/429235/2010+ford+f150+radiator+fan+stays+on Related Articles Radiator Hose Blew Off And Car Won’t Start? Reasons And Solutions To Fix It! Ford F150 Hard To Start When Hot? 9 Causes And Solutions to Fix It! Changed Thermostat Now Car Won’t Start? Everything You Need To Know! Car Won’t Start After Fuel Pump Replacement? All You Need To Know! Car Won't Start After Replacing Fuel Filter? 10 Causes And Solutions To Fix It! Car Won't Start After Replacing Crankshaft Position Sensor? 8 Reasons And Solutions To Fix It!