Ferrari 308 GTS coolant temperature question

Means the gauge and sender are working!

Absolutely normal!

 

Yes, normal operation. This is how all gauges used to work. Basic analog circuits. They changed their readings in real time with the changing signal from the sensor. Most modern cars have gauges that read in a narrow digitally controlled range (so owners don't worry and complain) until things go awry, then they will show actual values.

 

Coolant level sounds right. On my car the coolant level tends to be about halfway, more or less, in the expansion tank (where you fill). If you overfill it, the car will puke out the excess until it's happy, then will settle about where you are seeing it now.

Asking about coolant is like asking about oil. Everybody has an opinion, and there are many conflicting opinions. FWIW, I use Sierra propylene glycol coolant (pet safe) in all my older cars and change it every 3 years max. The brand isn't terribly important, IMHO, if you are doing frequent changes.

If you are more cautious, you can use one of the OEM brands from Porsche/Mercedes/BMW.

 

Zerex G05

There is some brass, solder in the radiator and a brass water pump impeller. Most modern coolants are for cars with aluminum and plastics. Some old head gaskets also dont mix well with modern coolants.

The Zerex G05 looks like the appropriately benign chemistry.