Your heater runs on engine coolant
Most drivers do not know this, and it explains a complaint that otherwise makes no sense: the heater that stopped working on a vehicle that has never overheated.
Cabin heat comes from a small radiator called a heater core, fed by the same coolant that circulates through the engine. When the heat drops off, the usual causes are a low coolant level, a thermostat stuck open so the engine never reaches temperature, air trapped in the system, or a heater core partially blocked.
Not one of those produces a high temperature gauge. The vehicle appears healthy and the cabin is cold, and the fault is in the cooling system the whole time.
In a place with winters like this one, that is worth treating as a repair rather than an inconvenience.
Coolant is a fluid with a service life
It does two jobs. It stops the system freezing, and it stops the system corroding.
The freeze protection can be tested, and it should be, because every top-up with plain water dilutes it. The corrosion protection cannot be seen at all: the additives deplete with time whether the vehicle is driven or parked, and depleted coolant looks exactly like fresh coolant.
What depleted coolant does is let the radiator, the heater core and the water pump corrode from inside. A fluid change deferred long enough becomes a radiator, and sometimes the heater core, which costs a great deal more than the fluid.
What a service covers
The radiator, pressure cap, thermostat, hoses, water pump, fan and the coolant itself.
Hoses are judged by condition rather than appearance, since they degrade from the inside. A pressure cap that no longer holds pressure is a small part that lowers the boiling point of the whole system.
About this store
The Idaho Falls consumer store handles cars, SUVs, pickups and light trucks, and is managed by Adam Word, open Monday to Friday, 8:00 AM to 5:00 PM. See also scheduled maintenance and engine repair.
See the national cooling system page for all 33 locations.