Had a spare cap that i threw on it and was still the same! Pump is a possibility but coolant is going through the whole system and can feel the pipe get hot once the thermostat opens.

Its due a cambelt and pump an its something that will be done in the next few weeks so will be another possible eliminated.

Dodgy gauge is what i was thinking but the OBD port gets the readings from the ECU which is the same place the gauge will so kinda eliminates the dials.