As Pete says , you should be able to see some coolant in the reservoir ( assuming it is the opaque type and not the dense black type ) ; there should be max and min level marks on the side .The oil temp gauge is visible on the left side of the cockpit display under the engine menu (at least I think it's a temp gauge). I saw the temp of the oil creeping up just after the oil message appeared on the main dash behind the steering. The oil temp reached 133 (into the red zone) . If I'm correct the coolant reading is on the right side of the dash but this did not give a high reading yesterday, even though the coolant tank felt very hot ? Normal . There is clearly leak of pink fluid on top of the coolant tank and below it. When I look at the tank from the side I can't see any pink fluid in the tank through the white plastic, not sure if it should be visible ? I did not remove the lid to look inside.
If the reservoir is empty there is not enough coolant in the system . The cap is a spring loaded type meant to contain the normal pressure in the system when hot . When in a pressurised system the water temp can rise above 100deg C without boiling : this is ‘superheated’ water , where boiling is contained by pressure , BUT if there is a leak then the superheated water will turn very quickly to steam as it finds a way out . This can be very hazardous- hence caution required if removing the cap when the system is hot . The cap releases in two stages ; the bayonet fitting will , at the first part of the turn , release pressure on the spring , and can be used to slowly release pressure from a hot system ( best done using a substantial piece of cloth to protect your hand , then when all gas/vapour has been released , the cap can safely be removed . Even then , with a part empty system which has run low , remaining water can boil and bubble inside the engine and scalding hot water can still erupt unexpectedly from the open reservoir..... how do I know this ? . Got the T shirt ...
In short , the only completely safe time to open that cap is when the engine is cold ; if you must add water at the roadside , use extreme caution and expect steam/scalding hot water to come out . If done carefully , with something to protect you , it can be done .