pull off the housing (3 bolts in front of engine. its black or silver and is a kinked pipe with a bubble in the middle.)
housing can be pulled out between fan blades( with a bit of work, but dont go overboard)
remove thermo (replace ALL gaskets)
put in new one w/gasket (get a low temp one, maybe 70deg/80deg.)
put housing/gasket back on
dont 4 get the 3 bolts...
WAIT: i forgot 2 tell u to drain the coolant/ flush it/refil it/ and get the air out of the hoses. check the FAQ's for that if ur not sure.