Permanent oil cooler vs thermostat

[Deuce Cam]

Is your car equipped with air conditioning?

If not you can easily remove the glove box, and then disconnect the tube leading to the heater core box (shown below, mounting screws circled in red):



At that point you should be able to see the heater core and blend door. Move the temperature knob on the hvac panel and see if the flaps are allowing air to pass through the core. You can alter the range of adjustment by moving where the sheath on the black cable is clipped in place on the heater core housing.

I would also check the hvac panel to make sure it didn't break where the cables attach. It's a somewhat common proplem due to the poor design.

If that doesn't fix the problem you might have a clogged heater core. This is all assuming your thermostat is operating correctly.