Q: Heater not working reliably, is it caused by a bad thermostat?

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During winter last year, upstate NY... like 10 degrees outside, drive to work...NO HEAT... 20 minute ride and i warmed car up for 10 minutes before i left for work. no heat... other cold days, will be driving and heat on and NO HEAT, then in an instance HEAT... i figure thermostat bad...opening inconsistently. sound like the issue? two days ago, had 37 degrees here in NY state...drove to work...NO HEAT...just blowing cold air. Driving home later, got heat.
thanks tom

My car has 88000 miles.
My car has an automatic transmission.

From what you’ve described, it sounds like you have a stuck open thermostat. I’d recommend replacing the thermostat to see if this is the cause of the slow heat up of the vehicle since it’s a relatively quick repair. In an area like that it sounds like you’ll will need the heat in the winter very badly and as soon as possible. I would also recommend getting a coolant flush as it may help clear any possible blockage in the heater core. To avoid any unnecessary repairs, consider YourMechanic, as one of our mobile technicians can come to your home or office to diagnose your heating issue and make the necessary repairs.

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