1.9 tdi 55 plate skoda super 150k miles.

Been noticing my tempreture gauge fluctuating. Does not get to 90 on local driving but on motorway ok. More persistent when u start the engine, once I start motorway driving it goes ok and stays ok.

Any idea what it can be?

It's normally the water temperature sensor failing. Cheap to replace and very common.

Thermostat stuck permanently open.

Gonna change thermostat and temp sensor this weekend

Temp sensor 5 min job, cheap too (£16 GSF)