Modern cooling systems rely on a temperature-activated switch to signal the electric radiator fan to engage once coolant temperature exceeds the design threshold — typically between 85 and 100 °C depending on the vehicle. The switch sits threaded into the radiator or coolant housing and contains a bimetallic or thermistor-based contact that closes at the trigger temperature, completing the circuit to the fan relay or control module. When this switch fails in the open position, the fan never receives the signal to run, and the engine climbs to the point of overheating in slow urban traffic where there is insufficient airflow through the radiator. This is the most serious failure mode, because even a single severe overheat can warp a cylinder head or damage head gasket sealing. A switch stuck in the closed position causes the opposite problem: the fan runs constantly even when the engine is cold, increasing electrical load and causing noise complaints. FAE and MTE-Thomson are two established suppliers stocking temperature switches referenced to OEM specifications across a wide range of VW, Opel, Peugeot, and Fiat applications. Because switching temperatures and connector orientations differ between even closely related engine variants, the OE number is the critical identifier — fitting a switch calibrated for the wrong temperature threshold causes chronic under- or over-cooling with no obvious external signs until engine damage is already under way.
Temperature switches are calibrated to specific switching temperatures and use connector bodies that are unique to each vehicle application. The OE number encodes both the activation threshold and the thread size for the radiator or housing port. Use the make-model-engine selector on this page to identify the correct unit. Even within the same engine family — for example, different power outputs of the same VW or Opel engine — the fan switching temperature can differ, so the OE reference is the only way to ensure the fan engages at the right coolant temperature for your specific variant.
OEM-specification switches from FAE or MTE-Thomson are calibrated to the same activation temperature as the original, use the same connector housing, and are tested for consistent switching over the expected service life. Aftermarket switches from reputable suppliers meet these calibration tolerances closely. Budget alternatives may use looser temperature calibration tolerances, which means the fan engages too early (constant running, high electrical load) or too late (overheating risk), neither of which is obvious until symptoms develop.
Yes, with a basic multimeter. Remove the switch from the radiator and suspend it in a container of water that you then heat with a thermometer monitoring temperature. At the rated switching temperature, the switch should show continuity (closed circuit) across its terminals. If it shows open circuit at the correct temperature, or closes at the wrong temperature, replacement is confirmed. This test is particularly useful for diagnosing whether the fan circuit fault lies in the switch, the relay, or the fan motor itself.
The most common and serious symptom is the radiator fan failing to run during slow traffic or at standstill with the engine at operating temperature, allowing coolant temperature to climb into the red. A temperature gauge that rises steadily above normal in traffic but returns to normal once the car is moving points squarely at the fan not activating. Conversely, if the fan runs immediately on every start regardless of coolant temperature, the switch is stuck closed. Either condition warrants replacement before engine damage can occur.
Showing 100 of 1,627 Radiator fan temperature switch OE numbers. Enter the OE on the main OE search to jump to any reference.
