Check the head gasket and the intake, both are common problems on that car
possibly the water pump
do i need to change the manifold when replacing thermostat
yes
most likely heater core leaking
100
It's under the throttle body housing. I'm looking for an answer on how to take the housing off to get to the thermostat
Replace the thermostat.
Drain the coolant. Follow the top radiator hose to the engine and this is usually where the thermostat is housed. Usually 2 bolts hold the housing on. Pull them and take note of the position of the thermostat, the spring should be engine side. Clean all mating surfaces good or leaking may occur. Reassemble and fill with coolant. Run and check coolant again.
If the pump is leaking or noisy then assume it is failing.
Sounds like head gasket is leaking
the location of the thermostat is under the throttle body.before you put it back on you need to buy some gasket sealer or a gasket for the thermostat
Remove the water supply hose from the top of the thermostat housing. Remove the thermostat housing retaining bolts. The old thermostat will simply lift out. Reverse the process to install the new thermostat.