I have a problem with my 91 SI..
 

My heat gets hot sometimes and cold sometimes. Temp gauge is a little over cold. Now with this said. Is that a sign of a thermostat going bad.

I also checked my antifreeze level. Good to go. Radiator hose feel normal. Now if it is can this cause any engine damage like head gasket etc.. Also should I go to Autozone or dealer & what thermostat do I purchase for. I have a 1 gen B16.

Now is this hard to install. It's too cold for having heat blowing out cool air.

Any help greatly appreciated:cool:

Probably need to adjust the heater valve (near fire wall in engine bay) and the heater core damper door (inside car, stiff wire push/pull control on passenger side of heater box).
The factory manual has instructions.

Take Care,
ChrisS

How to get a hold of a factory manual since it's a 91.

Hot sometimes and cold sometimes, kinda sounds like poor flow into the heater core. Yes i'd check the flow valve, it's right by the fuel filter attached to the heater hose into the firewall, make sure it is being properly actuated by the heater control knob. The blend door cable is best seen under the passenger side footwell under the center console. Also, you could check for antifreeze leaks, might be air in the system.