Hi, i started car (1.9sdi 2002) yesterday and the temperature warning light flashed at me, yet after turning off ignition and starting again it was gone. Checked coolant level today and it is about 1cm below the min line, while its cold. Do i need to replace all the coolant or can i just top it up with a little water? Could i have a leak? thanks.

Could be a faulty coolant sensor in the expansion tank. If fluid level is fine, then its a cheap part to replace (bottle & sensor).

I think it was low though, about 1cm below the min line when its cold.

In that case, try topping it up with G12 coolant - at least thats what is recommended for the RS.

I wouldn't go mixing it with water TBH