Temperature reading
Q I recently bought a five-door 2015 Renault Megane Expression 1.5 dci (engine code BZ1) with stop-start. The car runs well and has no fault codes indicated, averaging 63mpg overall. However, the analogue temperature display in the speedometer never reads above the lowest section and has never reached the centre section, even after many motorway miles or town driving; my previous petrol model did this after a very short period.
I believe the temperature sensor is buried in the thermostat housing on the gearbox side of the engine block. Can you tell me if this possibly faulty sensor affects either the use of the cooling fan in hot weather or the engine management of running conditions? My local dealer feels there is no real issue, saying that the fan is controlled by another sensor in the cylinderhead, so the gauge is for driver advice only. Ian Fraser A From the data I have on your vehicle, the BZ1 variant has a water-cooled turbocharger that has its own electric pump to circulate the coolant. It does seem quite common for owners to comment on the low reading of the temperature gauge and this would appear to be down to the fact that the engine runs at a low temperature, rather than that the reading is faulty. There is not, as your dealer suggests, a different sensor for the gauge – the manual says there is just the one sensor in the thermostat housing.
The only check I would make would be to use a diagnostics reader to confirm the temperature reading being given by the ECU, which controls the operation of the coolant fan. Provided this appears to show a satisfactory running temperature, I would be happy that all the systems are working well.
I suspect Renault deliberately designed the engine to run at a cooler temperature due to the stop-start system, to ensure the turbocharger would not become overheated. As long as the heater in the vehicle is working adequately, I would not be concerned. If the heater seems inefficient, it could suggest the thermostat is not operating correctly, which would need addressing.