coolant temp sensor change.. help!

[Robert Lees]

As one possible cause of hesitation on my chin I ordered new Lucas temp sensor, got extendable 19mm socket and started to undo, , err fountain of coolant hadn't unscrewed anything, coolant tank, oil cap etc. What have I done wrong? . Drove car for about 5 minutes, parked up left 10 mins whilst cleaned black k&n filter, then tried to take sensor off.

[TJC46]

Driving your car if only for a short time will start to pressurise the cooling system. You need to undoe the pressure cap on the expansion tank, then when any pressure has been released replace the cap. Only DO THIS WITH THE ENGINE COLD! Once you undo the coolant temp sensor you will still loose some coolant. Just have your new sensor ready to swap over as quick as you can. Would suggest some ptfe or similar on the thread before you put the new one in.