Temperature gauge not working properly

Hi,

This sounds like you have two different problems. As far as the fuel mileage and engine shaking, has the check engine light come on while the engine is running? If it is, the first thing I suggest is to have the computer scanned for diagnostic trouble codes.

Here is a quick video showing it being done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scan tool. However, most parts stores will do it free of charge.

Once we know what codes are there, we will have a better idea what direction to go. However, if the ECT is not accurate then that can effect fuel mileage so let's start with this.

Have this done if the check engine light stays on or flashes when the engine is running and let me know what codes are found.

Take care,

Joe