Recently the engine temperature gauge on my Laguna (2 litre petrol engine) has started reading low - hardly moves off the bottom of the gauge unless I let it sit idling on the drive for several minutes. The gauge is dual function and shows engine oil level when the ignition is first switched on and that works fine so the gauge itself is OK. I'm pretty sure that the actual engine temperature is OK too and that the thermostat isn't stuck open because the bottom radiator hose stays cold until the engine has been running for a while and then gets warm as the thermostat starts to open. Heater temperature also seems about right.
The sender unit is fitted into the thermostat housing and is simply held in place by a clip - not a screw in type. This suggests to me that it isn't going into the actual water system so can be simply pulled out and replaced but the Haynes manual isn't very helpful in this area. I've got a new one from the Renault dealer but the resistance when cold measures very close to the one on the car so I'm not convinced that the existing sender is actually duff. It may well be a problem with the regulated voltage that feeds the gauge/sender, the circuitry of which is gonna be hidden up behind the dashboard somewhere - something I don't fancy fighting my way into. Has anyone else changed a Laguna temperature gauge sender and if so, can it be simply pulled out of the recess it sits in without having to partially drain the cooling system? Also, could anyone tell me what voltage is fed down to the sender so I can check on my Laguna to see if it's low.