Nissan Repair Questions? Ask a Mechanic for Answers ASAP
If this is a 1.0 micra then your doing it right.
Just remove the hose, then the bolts, then seperate the housing. Now the housing can get pretty hard to seperate over time the gasket and coolant combined make for a really strong seal. The housing is aluminum though so you have to be careful not to crank it or chip it.
One thing you can try without marring it up is to take a wood dowel or handle and put it in the neck to where the housing flares and slowly push down while tapping by the seal with a rubber mallet. This almost always will cause it to come apart starting at the top and you can pull it apart.