How to fix a faulty thermostat on a Vauxhall Insignia?

I have been experiencing issues with the thermostat on my Vauxhall Insignia, the temperature gauge constantly fluctuates and I have noticed a decrease in fuel efficiency. What steps can I take to fix this issue?

First, make sure the thermostat is the correct type for your vehicle model. If it is, then the issue may be due to a faulty thermostat or temperature sensor. I suggest taking your vehicle to a trusted mechanic to have them diagnose and replace any faulty parts.

Have you recently replaced your coolant or experienced any overheating issues? If so, it's possible that there is air trapped in the cooling system, causing the inaccurate temperature readings. Bleeding the cooling system can help resolve this issue.

Another potential cause could be a malfunctioning temperature gauge itself. You may want to consider having it replaced if all other troubleshooting steps fail.