Posted on 11/5/2026
If your heater blows cold after the engine has warmed up, either hot coolant isn't reaching the heater core or the air isn't being sent across it. Most of the time the cause is low coolant, a thermostat stuck open, or a blend door that has stopped moving. Your car's heater doesn't make its own heat. It borrows it from the engine. Coolant picks up heat as it circulates, flows through a small radiator behind the dash called the heater core, and the blower pushes air across that core into the cabin. Break any part of that loop and you're scraping the inside of the windshield on the way to work. Start With Your Temperature Gauge The temperature gauge tells you more than anything else, so check it before you do anything. Gauge reads normal, heat is cold. Usually low coolant, a clogged heater core, or a blend door problem. Gauge stays low or takes forever to come up. The thermostat is probably stuck open, so the engine never gets hot enough to make real heat. Gauge ... read more