Answer:   Without actually “seeing” your vehicle, it is difficult to diagnose the problem.  We are not so sure the thermostat is the problem.  You may not be getting any hot coolant flowing through the heater.  The heater control valve may be faulty.  In addition, check the vacuum lines that control the doors and the heater ducts.

Question: 2001 Jeep Cherokee mileage: 180,000.  I had a problem with the heat, it was only luke warm at best. I replaced the thermostat and still have the same problem.  My temperature gauge also confirms I am running much cooler than the 195 degree t-stat setting.  I also partially blocked the radiator to see if I could get the temperature up, but that did nothing as well. Could it be a faulty t-stat or should I look elsewhere?

Answer:   You may have a faulty thermostat or possibly incorrect gauge readings.  Remove the thermostat and check it when it is cold to see that it is closed.  Put the thermostat in a pan of hot water on a stove.  The thermostat should be open when the water is near boiling.   If the thermostat is okay, the temperature sensor may be your problem.

Question: 2003 Ford Windstar mileage: 40,000.  Not getting hot heat only luke-warm, but hoses are hot.

Answer:   The heater core may be plugged, restricting the flow of hot water.

Question: 2001 Pontiac Grand Am mileage: 124,000.  Hi.  I have a 1993 Grand Am with a High Output Quad 4.  The blower motor for the heater/air conditioning suddenly stopped working.  I checked the fuse, and it was OK.  When I change the heater settings, I hear the usual pneumatic sounds that go with it, so I know that the car is responding to the controls, there just is not any forced air.  If it's of any consequence, I just had the alternator replaced 2 weeks ago, due to a very obviously bad front bearing.

Answer:   First check to see that you have 12 volts to the blower motor.  If yes, blower motor has probably failed.  If no, it may be the blower motor relay or there is a speed control resister causing your problem.

Question: 1999 Mercury Sable mileage: 71,000.   Heater would blow hot and cold at different times. I pressure tested radiator and found a leak in the intake manifold.  The heater also gargled at times when low on water.  I repaired the manifold leak, checked the compression (all six at better than 150 lbs.) have a new thermostat and radiator cap.  Still the heat comes a goes and the heat gauge goes up high at times.   At my wits end.

Answer:   Check operation of radiator fan.  A partially plugged radiator may be causing your problem.  Replace radiator with new, and your heater core may be partially plugged also.

Question: 2005 Chevrolet S10 Pick Up mileage: 17,000.  Last winter, heater with fan on never really got hot, only warm.  A month ago, the temperature gauge started to show running hot, but not in red/danger, but close.  I flushed system.   Replaced coolant.  Also replaced thermostat.  Now, 1.  Low coolant warming signal stays on, even though cooling system is full; 2.  Engine runs on cool side barely above cold, and 3.  Heater still does not blow hot air.  Any ideas?  Thanks

Answer: Test the low coolant sensor by removing the wire and check the warning light.  Also, ground the wire and check the light.  If okay, the sensor may be faulty.  From what you describe, you may have the wrong thermostat.  Your car should have a 195� thermostat.  This will also help the heater with hot air.

Question: 2001 Chevrolet Truck 1500 mileage: 70,000.  My heater is not putting out warm air. Blower is working fine but air stays cool and doesn't heat up as engine temperature increases.  I'm told it’s either a plugged core or a defective heater control valve.  Where is the control valve?  How can I determine what's wrong?

Answer:   The heater control valve is on the top of the engine with a heater hose attached.  Check for flow or coolant out of the valve.  Test the heater core by checking coolant flow out of it.

Question: 2004 Mazda B3000 truck mileage: 45,000.  All of a sudden the heater motor stops blowing.  I ran a hot wire to it and it works, fuses good, grounds good.  All I can figure is the switch.  Anything I might have missed?  I'm an old VW'er we never have these problems, but my wife wants to be warm.

Answer:   In the heater duct there is a blower resistor for different fan speeds, which may have failed.  Also, check the blow fan relay.

Question: 2002 Chevy Cavalier mileage: 69,000.  The heater does not work properly.  Can have the hi/low switch in any position and it still only blows slow but the sound increases with a higher setting like it is blowing hard but it isn’t.  This problem happens with the heat or air-con.  Getting cold here in Minnesota trying to get fixed before the sub-zero temperatures come thank you.  How much will this repair cost?

Answer:   The doors in the heater ducts may not be working properly.  They are controlled by vacuum.  Check for vacuum hoses that may be cracked or a loose connection.  Another source of the leak may be the vacuum switch on the back of the heater/air condition control on the dash.  Somewhere in the vacuum system is a check valve that may have failed.  It is usually part of the vacuum reservoir tank.

Question: 2002 Chevrolet Lumina APV mileage: 64,000.  The heater is steaming the windshield inside the car. I have to wipe the windshield with a rag to see the road when driving.

Answer:   Your heater core has probably failed and is leaking coolant.  The hot coolant turns to steam.  Replacing the heater core should fix your problem.

Question: 1998 Chevy Camaro mileage: 60,000.  I have a problem with my heater it will only work in defrost mode When I slide the control to any other setting it stays in defrost.  

Answer:  Check for vacuum hoses that may be cracked or a loose connection. Another source of the leak may be the vacuum switch on the back of the heater/air condition control on the dash.  Somewhere in the vacuum system is a check valve that may have failed.  It is usually part of the vacuum reservoir tank.

Question: 2003 Ford Ranger mileage: 64.000.  Heater won’t heat blowing cool air.  I’m thinking about changing thermostat. Any ideas?

Answer:  The heater control valve may be stuck closed or the vacuum hose is loose or not getting vacuum to open it.

Question: 2002 Ford Focus mileage: 78,000.  No heat in car.  Seems to be blower problem.  Nothing happens when I turn on heat or A/C.  One moment heat...the next time I started the car, nothing!  Is it a fuse?  If so, which one (no manual here).

Answer:  With a test light, test all fuses with the key on and the heater fan on.  Some fuses test okay without a load.

Question: 2001 Ford F-150 mileage: 125,000.  Heater not blowing hot air.  I have already replaced the heater core, the thermostat, and the anti-freeze.  I have even checked the cable that activates the door that is supposed to allow hot air into the ductwork.  Am I missing something?  Any other possibilities?  I don't mind the cold it's just hard to see out the windows when it snows and ice's.  The A/C works just fine!  Let me know what you think!

Answer:  The heater control valve may be stuck closed.  Also, check vacuum source to valve.

Question: 1999 Chevy Cavalier mileage: 176,000.  I just recently purchased this car, and I was wondering why is it when I turn the heat on, it smells as if it were heating up although the temperature gauge doesn’t seem to show it? It smells like antifreeze.  Is there any thing I can do or fix?  

Answer:  The heater core is probably leaking coolant.  This could be the source of the “coolant” smell.  The heater core will need replacing to fix your problem.

Question: 1999: Ford Windstar mileage: 110,000.  Problem is no heat: have replaced heater core 1 yr ago new radiator less than 1 month ago, replaced thermostat less than 1 week ago.... new antifreeze too.

Answer:   The heater control valve may be stuck shut or the vacuum hose has come off. 

Question: 2002 Dodge 1500 truck mileage: 80,000. Heat is on/off at no regular timing heater fan is in High and switch has no control of fan speed-- climate control--a/c-- have replaced thermostat, inline heat control on upper radiator hose, and heat sensor on intake manifold. Replaced water pump as well. Any advice?

Answer: Your solid-state fan speed control module may need replacing.

Question: 2004 Mazda 3 mileage: 35,000. Heating does not work. I changed the thermostat and added clean fluid. Hot water does not go into heating core.

Answer: The heater control valve may not be working properly by not allowing hot coolant to the heater. The valve is vacuum operated and they hang up or the vacuum hose gets loose.

Question: 2003 Chevy S10 Pickup mileage: 86,545. What would cause me not to get heat for my Def or heater, I have the proper fluids in my coolant system, but I do smell antifreeze when the engine is warm. My temp gauge is always around 210 or lower. Could this be as simple as my Thermostat, or something more serious? I would appreciate any possible links that I could check out myself. The only possible heat I get is if everything is turned off and my temp dial is in the red, after driving for some time I can switch it to either Def or heat and I get a small exchange of heat before turning cool again.

Answer: The heater control valve is probably not opening. It controls the coolant flow from the engine through the heater hoses to the heater. The valve may be stuck or the vacuum hose may not be attached.