94 Voyager Heater core and engine question

94 Voyager 3.3 auto

I just bought this vehicle, it shows 193,000 miles on odometer.

The engine and tranny run fine except that the engine seems to have back pressure in it. (By back pressure I mean that the coolant is continullay pushed back out the radiator with cap removed and I can see air bubbles in the coolant reservoir with cap on.)I removed the thermostat just to see if coolant will circulate, but still seem to have back pressure with the engine temp at normal. One thing I did check is that the hose to heater core is warm to touch (hose with the control valve on it-passenger side) The driver side hose stays cold to touch so I am thinking that the core is plugged. I am thinking of just getting a pipe nipple and hooking the 2 hoses togther and by passing the heater core temporaly.

My question is: Will a heater core that is plugged prevent coolant circulation in the engine and cause the backup pressure?? If the heater core doesn't affect the circulation then I am thinking it could be a head gasket. I plan on getting some Bars Leak-Block Seal and Head Gasket Fix once it circulates.

I want to make sure the coolant circulates before I go further.

Thanks for any advice.