Doesn't matter which way the water flows. The heater core is just a tube with fins and water can flow either direction.
Look near or behind the alternator. The valve that controls flow of coolant to the heater core on my 1987 Aerostar is located on the left wall of the engine compartment. I imagine the 1991 is similar. Trace the heater hoses from the engine/water pump and you will find it.
You can bypass your 1988 Buick Skylark heater core by removing the heater core water supply hoses. There will be to water hoses. Connect the water hoses to each other.
you should check to see that heater hoses are connected through the fire wall and they are connected to the heater core.
could be a number of things radiator,thermostat,water pump heater core, low coolant old coolant bad hoses,
Remove the water supply hoses from your 1993 Chevy Corvette heater core. Some water will drain out of the hoses and the heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
The heater core, in a Saturn and 1200, is held in place by four bolts and two water hoses. Remove the bolts and the water hoses. The heater core will come out. Reverse the process to install the new heater core.
Bolt the heater core into place, with the four retaining bolts. Connect the water supply hoses. You might need to bleed one of the hoses to get the water flowing through the heater core.
rad hoses route coolant to the engine to maintain operating temperature (to keep engine from overheating). Heater hoses supply the heater core (inside most vehicles) with hot water, when heater/ac temperature control knob is turned toward hot, to heat the interior of the vehicle by opening and closing a water flow control valve allowing water to enter the heater core for heat. =;)
you may not have the heater water hoses plugged in
This fluid can leak from many places. Look in places where water hoses meet the engine, where the heater hoses go into the firewall, the radiator and your heater core.
heater coil
the heater core water pump hoses including the heater hoses