Over heats new thermostat hest almosts pegs then comes down

First, your engine will heat up to the temperature that the thermostat is rated for and when the thermostat opens the coolant will flow through the radiator and start to cool down. In order to have heat in the heater, the coolant must pass through the heater core. To find out if that is happening, locate the heater hoses and when the engine is warm and running touch them to see if they are hot. If they are not hot then there is a blockage in the heating system.

probably a faulty temperature sender unit
temp sensor unit which controls the fan)

disconnect the heat hoses going into fire wall , put hose into one with pressure and flush as it sounds like it could be bloked in the heater core,the other thing that could be the problem be the hot ,cold switch as it restricts the flow to makes the heater hoter or colder , it might need tlc or replacing as it is manaul not elec

No heat sounds like the heater core isn't circulating. Dropping down, sounds like the thermostat is sticking for a while than working. That can be checked by feeling the hose when the temp is up. If it is hard at the hose where the flow goes in; I would consider changing the thermostat. It can be a bad circulation problem killing the themostat though.

Hello,

You problem sounds like a "Blend Door" issue, you have these doors that open & close and everything in between to adjust air temp. These doors have a "peg" that is connected to an arm or wire just like on a ten speed bike to shift gears, that peg may have broken off.

Another issue may be a stuck open thermostat, if you have a temp gauge is it running at normal temp? If the thermostat is stuck open then heat may become an issue.

I have found several 2007 Chevrolet Impala blend door issues here in fixya.com.

Hope this helps.

It could definitely be the thermostat. It is a cheap part to replace. If the car overheats while running down the road (not stop and go traffic), then it is almost certainly the thermostat.

is the car over heating to the point the over heat light comes on and/or gauge pegs out max heat ?
if so u probly need a new water pump.
or is the a/c just warm air ?

Your overheating problems can have several possible causes.
1) Airlock in heating system - solution - bleed air from cooling system. Method is dependent on make/model of vehicle
2) Radiator blocked - solution - drain and flush radiator
3) Failed waterpump - solution - fit new waterpump
4) Engine thermostat stuck in closed position - solution - fit new thermostat
5) Electric cooling fan (if fitted) failing to operate - solution - check fan, fan operating switch, all wiring and connectors
6) Not enough coolant in system - solution - check and top up to required level. Also check all hoses for sign of leakage.
7) Faulty temperature gauge giving incorrect reading

did you put the thermostat in with the proper end facing the engine block ? also is all the air bled out of the system ?