Heat that comes and goes with engine speed
Here is a pattern worth recognizing in cold weather. The heater blows warm on the highway, then turns lukewarm or cold while the vehicle idles at a light or in a driveway. Speed up again and the warmth returns.
The heater is fed by hot coolant from the engine. When there is plenty of coolant in the system, it reaches the heater at any engine speed. When the level is low, or air has got into the system, the pump only pushes enough coolant to the heater when the engine is turning faster. At idle it falls short.
Which means a heater that fades at idle is often an early sign of low coolant, before the temperature gauge shows anything at all. It is the cooling system reporting a problem in the one place the driver can feel it.
What to do about it
Check the coolant level in the overflow tank with the engine cold. If it is low, the question is where the coolant went.
- A leak may show as drips under the front, a damp hose, or a crusty residue around a fitting.
- No visible leak with a level that keeps dropping is worth having pressure tested.
- Air in the system after a recent repair can cause the same symptom, and the system needs bleeding properly.
Topping up gets you home. Finding the cause keeps the engine safe, because the heater is only the first place low coolant shows up.
In the same building
Engine repair handles anything the cooling fault turns out to be connected to, and the cabin side of things is A/C service. The national cooling system page covers what to do if the gauge climbs.
Other stores nearby
De Soto and Paducah, KY also offer cooling system service.
About this store
The Jackson store runs seventeen services and is managed by Mike Rhymer.
See the national cooling system page for all 33 locations.