Coolant level

[kton2002]

Had my bongo 2.0 in for a few bits and they inspected thermostat. Didn’t get chance to replace it as part didn’t arrive but thermostat housing went back on, with a bit of sealant for good measure. No Leaks there that I can see. However coolant has been very slowly (1/2mm) reducing when I use it. Could it be stabilising since the housing was removed due to air getting in there at the time?

[g8dhe]

In the past weeping from the water pump (at least on the diesel) has also been a cause as it only happens when the engine is running, not sure if this could be a similar problem on the petrol 2l ?