coolant temp sensor mate,i changed mine and its literally a 5 min job,on the RHS of the engine under the small perforated plastic cover is a small plug with either a green or black body. there is a small plastic c clip holding it in,when the engine is cold remove it and replace with a genuine OEM item,you will lose the contents of the cooland ball in the process so be ready to top it up again when done,warm the engine slowly with the bottle top open and keep an eye on the level,top up as necessary