Temp gauge issue

[BetterCallPaul]

Hi All,
I am looking for a bit of advice about an Issue I am having with my 93 T4 Cali Diesel.
I am currently on the road in Spain and after 40 days of mostly issue free driving the tempreture warning light has suddenly come on twice in the last two days. Both times while driving up some steep hills I might add. The tempreture needle is also now going up very quickly to 90 degree mark or above after only a few minutes of driving in low gear.

I have had to stop twice to let the engine cool down and I have also had to top up the coolant tank twice after it cooled down.
The type of coolant used was this one - https://rlub.es/rparmqd - and it was filled up to just at the min level. Engine oil is full. No sign of coolant leak and the only visible issue to the engine I can see is that some of the rubber padding has detached from a hose. (See picture of coolant tank).

I have stopped driving at the next village and will be getting it looked at tomorrow by a garage. Since I am in rurual Spain the mechanics don't speak any English.

Would anyone be able to suggest some possible causes and how serious it might be. I plan to google some terms in Spanish and be a bit prepared for the conversation tomorrow.
So far my research online has suggested it might either be
Temp gauge sensor fault
Coolant leaking
Oil and coolant mixed together
Head gasket issue- which I know means mas problemas y dineros : )

I've tried to add some pictures/ video to show whats happening.
Thanks,

 

[BetterCallPaul]

I wanted to give an update on this in case it helps anyone. The two mechanics who listened to my description of the issue - in fairly broken Spanish - and looked at it for a few minutes did not seem to be concerned that there is a problem and told me to top up the coolant level to closer to the max when it has cooled down. The coolant tank itself is quite hot after a short drive but the engine block itself is not that hot. This is despite the temperature needle going to just below the 100 degree mark. The red light has stayed off since and I have started to drive with the heating on when it does go above 90. The heating itself does not seem to work - as in it blows but not very hot - at least not as hot as it did before when turned up to the max.

So long story short I was told I am fine to keep driving but to continue to keep an eye on it. So I'll continue going for the rest of the trip but much slower, and much shorter journeys and a bit nervously too.
Fingers crossed Betty will get fully back to normal.

Cheers,
PJ