I hope someone can help me here??

My daughter has a 1989 LS Integra manual car. As she is overseas, I have been driving it occasionally. Today, I took it to work and it was fine but later on I went out and the temp guage immeadiately went to a bit over half way. And the engine was COLD. I couldn't see anything wrong so I drove it and the guage then went as hard against the hot mark as it could go.

I stopped a couple of times and it was running fine. No sign of overheating at all so I just kept driving it.

I let it get stone cold when I got home then tried it again. Same thing.

Also, for a long time now, the fuel gauge will not show FULL when it is full. It goes up to two/thirds of the way and that's it.

Has anyone got some thoughts on the temp gauge problem and how to solve it?
Thanks