Engine takes a long time to warm up, cold heater
When the temperature gauge doesn't rise to the working zone and cold air blows in the cabin, driving becomes uncomfortable. Most often, the problem lies in the engine cooling system, which can't reach the required temperature.
Likely causes — most common first
Thermostat stuck in the open position
This valve lets coolant flow through the small or large circuit. If it's stuck open, the coolant goes straight through the radiator and the engine can't warm up.
Low coolant level
When there's too little coolant, circulation is disrupted, and hot liquid can't reach the heater core, making the heater blow cold air.
Airlock in the cooling system
Air bubbles block the normal flow of coolant, causing uneven heat distribution and a cold heater even when the engine is warm.
Clogged heater core
Over time, dirt, scale, or remnants of sealant from previous repairs accumulate inside the small heater core. This prevents the hot coolant from transferring heat to the cabin air.
Faulty auxiliary pump or sensors
Many modern cars have an additional electric pump that helps circulate coolant through the heater at idle. If it's not working, cold air blows from the vents at traffic lights.
