No. It sound like the cooling system has an air pocket. Have you recently done any repairs/mods in which you had to monkey with the cooling system?
If the core was PLUGGED it would not circulate at all. It could be that it is PARTIALLY plugged. Try removing the heater hoses at the Heater control valve and purchasing a back flushing t at a parts store, and back flushing through both sides. There will be junk to come out. You also want to ensure the control valve itself is fuctioning by testing the little valve on it.
Hope it helps.
Look up a how to on a coolant flush. Flush the whole system, and be sure to do the heater core sepertly. Good practice to replace thermostat and gasket while your at it.
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