Can anyone tell me if you need to bleed the coolent system, of impreza wrx if you change the water temperature sensor. As a few people who know scoobs have told me you donet need to and a friend who's a mechanic says you have to. I think hes wrong but I need reasurrance.

I had a 5 turbo in the past and I blew it up so often I darnt take any risks.
Any help would be appreciated!!!!
Regards Ronnie

 

Can't hurt to do it, even if it's not needed, can it?

 

But hows it done, if it does need bleeding. Ive left the top off???????