Question about 2001 Chevrolet Silverado 1500

2 Answers

What could cause my truck to have no heat?

Other than the thermostat, what could be wrong with my truck that would cause no heat to come out of the air vents? Temperature knob has been set at varying settings from medium to high, but no heat ever comes out. It blows cold air only. Engine temperature gauge stays consistently under 210.

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  • kenneth_w_we Feb 11, 2012

    Changing the thermostat is the current plan. I don't have a radiator cap per se, just a cap on the reservoir. Here are the specs of the truck:

    V6 - 4.3L vin W 262ci - MFI GAS OHV



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The heater radiator could be blocked or the valve controlling the heater could be faulty ,,,, carefully check the heater hoses ,, they are the small ones running from the engine bay through the bulkhead into the car,,,they both should be hot ,,, if one is cold the water is not circulating either due to a blockage or the heater valve not working ,,, if the car has climate control you need to be sure that it is serviced properly as this system mixes the hot and cold air,, also at 210 you should have some heat , the best way to check if its the thermostat is to run the carstationary until it gets hot even if the thermostat is faulty the system will build up heat due to no cold air passing through the grill and coolng the engine radiator

Posted on Feb 11, 2012

Testimonial: "Ok, so we replaced the thermostat (even though it looked completely functional when we got down to It) since it was only $7. That didn't fix the problem (not a big surprise). So, we then followed your suggestion of checking the temperature of both hoses going to/from the heater core and only the hose carrying water into the heater core is hot, the other remains cold even after running the truck for 10-15 minutes. Temperature gauge appears to be working correctly, with it slowly climbing to right under 210 and then falling/rising consistently between 195-210. All of this leads me to believe that the heater core is blocked or otherwise broken. I do not believe there is anything like a "heater valve" on my truck. Any thoughts aside from replacing the heater core (or does that even sound feasible to you)? Thanks!"

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  • jeremiah horgan Feb 12, 2012

    when car is cold you could try disconnecting the heater hoses and running water through it using a garden hose but be careful you dont overdo the pressure because you could burst the heater rad if you over do it this might dislodge any blockage ...hope this helps

  • jeremiah horgan Feb 13, 2012

    did ya try that ,,,, let me know and i will do my best ,,,, funny but i might be from ireland but i am a mechanic with 29 years and i hate to have people give stupid advice and lead you wrong... always start easy and spend money later ,,,,, if water is hot going in and not coming out its a valve or blockage ,,, think about it ,,,, most newer cars dont have a valve but some do ,,, other than that its a blocked rad ,,,,

  • jeremiah horgan Feb 13, 2012

    and as im here watching for water circulating with a rad cap off dont work unless thermostat is open fully ,,,,, how can water swirl around with the thermo closed ,,, basically its another valve that dont open till water is really hot ,,,and if it aint open water isnt going to circulate so you would notice through the rad cap ,,,, and as i said 210 is plenty hot to get heat ,,,, if pump was faulty both hoses would be cold ,,, jesus!!!!!!

  • jeremiah horgan Feb 13, 2012

    and william is right only i say blocked or valve ,,, dont make me come over !!!!!!!!!!!!!!!

  • kenneth_w_we Feb 13, 2012

    jeremiah/william - The next plan is to try and gently backflush the heater core. Wish me luck. I'll post back how that goes later this week. Thanks!

  • jeremiah horgan Feb 15, 2012

    how ya get on ,,,,, let me know latest results


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  • 6 Answers

It could be a bad heater core

Posted on Feb 12, 2012

  • William Campbell
    William Campbell Feb 15, 2012

    did you try back flushing the heater core normally they arent that expensive to buy but sometimes they are a pain to replace depending on where under the dash it is located



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Next you need air flowing through the heater core so it can come out heated through your vents. If the iar is flowing somewhere else, your temp blend door is not moving because the bend door motor is bad or your temp knob on your heater controls is bad. The blend door motor is an electric motor.

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Air flow control is accomplished in the following manner:
  • Primary control is through the function selector knob , mounted on the heater function selector switch, which is part of the heater control .
  • The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
  • The heater function selector switch combines a vacuum selector valve with an internal electrical switch.
  • The vacuum selector valve directs source vacuum to various vacuum control motors (18A318) . Refer to the System Airflow Schematic and Vacuum Control Charts.
  • An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch (18578) .
  • The position of the function selector knob determines the manner in which the system will operate.
  • Each position of the function selector knob is detented for positive engagement.
Temperature Control
The temperature control operates in the following manner:
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  • This control knob is connected to a potentiometer mounted in the heater control . This potentiometer is electrically connected to the electric blend door actuator that operates the A/C air temperature control door.


  • Movement of the control knob from COOL (Blue) to WARM (Red) causes a corresponding movement on the air temperature control door and determines the temperature that the system will maintain.
System uses a reheat method to provide conditioned air to the passenger compartment.
  • All airflow from the blower motor (18527) passes through the A/C evaporator housing .
  • Temperature is then regulated by reheating a portion of the air and blending it with the remaining cool air to the desired temperature.
  • Temperature blending is varied by the air temperature control door, which regulates the amount of air that flows through and/or around the heater core (18476) , where it is then mixed and distributed.
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