Hey there, I have a 1991 legacy and I have installed a new radiator and thermostat and I am still not getting consistent heat in the passenger compartment. I get heat while I am going a decent speed, but before long, it starts blowing cold air. And as soon as I am idling, the heat cuts out and the temp begins to rise fast. All fluids are full and brand new. Any ideas?
You don't have enough coolant in the system, somewhere in the coolant lines there's an air bubble that is geting trapped in the heater core. This is really the only thing it could be so add more coolant and bleed out the air pocket and you should be golden.
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