There was about a pint of coolant under the carpet on the driver side, diagnosed as a heater core leak. Can I keep driving the car if I quit turning on the heater?
Is heater core going to leak water if I don't use the heater? on 1996 Ford Escort
Unfortunately the heater core will still leak. The best thing to do, if you can not replace the heater core is to have it bypassed, which is not very expensive, then you can drive your car.
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The best thing would be to bypass the heater core, it can be done easily, until you can get it replaced.