The typical reasons to replace this part are because:
- There is a damage bleed screw atop this part, or
- You’re replacing the thermostat.
It’s a good idea to replace the thermostat when you have this part removed anyway. In the past, I’ve lost an engine due to a bad thermostat (combined with a broken temperature gauge) so now I’m a lot more wary.
As part of the work, I use a new gasket (square, with bolt holes, made of a cardboard-like substance) and a new seal (round, black, made of a rubber-like substance).
The housing is attached with four 10mm bolts, two long and two short. Nothing very difficult there. A 1/4″ drive socket works well.
Much more tricky is the attachment of the lower radiator hose. Space is VERY tight. You are right up against the fan and radiator. I ended up using a 6mm socket on a 1/4″ drive because I couldn’t get either a nut driver or screwdriver to turn. And, I still ended up with a leak in that area.
The biggest danger is having the hose clamp interfere with (and destroy) the fan, I tried to make sure to check it for interference.