Jim Grant's Tech Tips
Chevy Cavalier, No Heat
Q: I have a '92 Chevy
Cavalier. It doesn't give enough heat. When it is cold outside and the
blower running at full speed, I can still feel cold inside and the part
(in middle) of front windshield remains foggy. Somebody told me that this
was due to a faulty thermostat so I had it replaced, the problem still
exists. Please advise.
have to answer these questions; 1. Is the coolant reaching proper operating
temperature? 2. Is there adequate coolant flow through the heater core?
3. Is the heating/ventilation system (doors, flappers and controls) functioning
properly? The thermostat which controls coolant temperature is most frequently
the cause of poor heat from a vehicle's heating system. You already replaced
the thermostat. (Hopefully with one that has the factory recommended operating
temperature.) What about adequate coolant flow? It's not uncommon for
heater cores to become internally restricted, reducing the heat available.
A quick check for restriction can be performed by comparing the temperature
of the coolant inlet hose to that of the outlet hose of the heater. If
there is a remarkable difference in temperature between the hoses, then
there is most likely a restriction. To confirm a restriction requires
checking the coolant flow rate through the heater core. Sometimes a restricted
heater core can be back flushed to clear it of the restriction. If that
doesn't work the heater core must be replaced. By the way, the most common
cause for heater core restriction is due to poor cooling system maintenance.
The least frequent cause of poor heat is the heating/ventilation system
(doors, flappers and controls). Many of the system components are made
of plastic and do wear and break with age, resulting in the inability
to control air temperature.