Ok your driving along all normal, suddenly your rad gets blocked (unlikely) temp gauge goes up stop clean back to normal did its job.
2nd most likely senario driving along BTM hose splits, the sensor is now in thin air no water to read temp, so i guess the first we know is when engine pinches up.
So would a level sensor in header tank not be a better idea.

The temp sensor when you loose coolant is not in thin air but in hot air or steam which is not cooler that the engine temp, it's a resistive NTC sensor it doesnt have to be in fluid to react to temperature.... that's not the main problem, the problem is that the gauge goes up from the middle only at 120*C so you can drive around for long with 110*C without even knowing it which is not healthy at all, if you want to be on the safe side an additional coolant temp sensor with on board gauge is better that a level sensor but if you fit both you are completely covered, for coolant temp sensor you dont have to cut a hose and fit addaptor which is the most commonly used method, you can do what i did, to drill into the elbow and cut athread in it




for level warning it's possible with a capacitive proximity sensor, relay and a buzzer, it's verified and works

Yes very good, i like the idea of the coolant level sensor.
You will have to tell me where and how to wire it in when you get 10 mins
Do you have a part number for the level sensor
Many thanks

For the level warning you need this http://www.ebay.co.uk/itm/DC-6-36V-...-Proximity-Sensor-Switch-1-10mm-/191102270689 , a NORMALLY CLOSED relay and a buzzer that's all, while coolant is above it's level it will keep the relay open and when it looses the target the feed to the relay's coil is interrupted, the contact goes to the NC position and the buzzer will sound, here's the scheme



or you can go the easy way http://www.ebay.co.uk/itm/Low-Coola...?pt=UK_Sound_Vision_Other&hash=item27cc0c14ae

Many thanks for that, very helpfull
Mark