Temperature sensors on thermostat housing

[PaulFDennis]

My 1.9DG has a coolant leak around one of the temperature sensors located on the lower thermostat housing. My understanding is that the 1.9DG engine only uses one of these sensors, the one located at the back of the housing when viewed from the rear of the vehicle. The other sensor, located on the side of the lhs of the housing is used for the 2.1 fuel injected engine. On my engine this sensor is plugged into the wiring loom but I assume is only used to plug the sensor position on the thermostat housing. Is this correct?

I haven’t removed the sensors but assume they are sealed with an o-ring. How is the seal made? The sensors don’t appear to be screw in and I’m assuming some sort of spring loaded locking mechanism is in place?

Any advice would be gratefully received.

 

[PaulFDennis]

I’ve now researched the forums. The two units are the temperature sensor and a switch for the manifold heater. They’re sealed with a viton ‘o’-ring and a plastic retaining clip.

 

[maxstu]

That's correct. Manifold heater and temp gauge. Some are held in place with plastic clips and some with metal clips.
It is belts and braces to add a smear of instant gasket around the o'ring. I use Hylomar blue. Not strictly necessary. But some do. I do.
It is fairly easy to change these sensors without losing too much coolant, as is the radiator fan sensor.

[PaulFDennis]

Replacing the ‘O’ rings sealing the sensors has fixed the leak. I also replaced the sensors at the same time since they only cost a few pound each. After I pressure tested the system and all seems okay. The old rings looked a little undersized, notably in terms of cross-section diameter. The old sensors were liberally coated in sealant/instant gasket and I suspect this had failed thus leaking when cold. When hot the ‘O’ rings looked expanded to become an effective seal.

I’ve read a lot about bleeding the cooling system in the forums and decided to use the GoWesty method with a bicycle pump fitted with a pressure gauge. It worked very well but I may have been fortunate. It also allowed me to pressure test the system and find a small leak at a hose connection. A small tightening of the jubilee clip seems to have fixed this.