Heat not blowing hot

Tiny
RICHSTRUCK
  • MEMBER
  • 2003 CHEVROLET S-10
  • 4.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 121,000 MILES
Have replaced thermostat, flushed heater core, still get heat sometimes, but does not last. Tested the temp control switch has 9.92 ohms, and it is variable with turn of the control shaft. What does this temperature control switch actually control? Is it a valve? The truck runs great. Runs about 210 degrees and is full with antifreeze. Does not overheat. It used to have heat really fast, the heater core has been replaced, and worked fine for a winter, it was working then it started to have sometimes heat.
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Friday, January 3rd, 2014 AT 12:09 PM

58 Replies

Tiny
SATURNTECH9
  • EXPERT
There is a temperature blend door actuator to control the temp. Here is a guide to show you what you are in fro when changing it out with the location of the actuator for you car below.

https://www.2carpros.com/articles/replace-blend-door-motor

this guide can help as well

https://www.2carpros.com/articles/car-heater-not-working

With the engine up to operating temp are both the heater hoses going into the heater core getting too hot to hold?

Check out the diagrams (Below). Please let us know what you find.

Cheers,
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Friday, January 3rd, 2014 AT 12:31 PM
Tiny
RICHSTRUCK
  • MEMBER
With the truck up to operating temperature, the supply hose (the larger of the two) is hotter than the smaller one?
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Sunday, January 5th, 2014 AT 7:01 AM
Tiny
SATURNTECH9
  • EXPERT
Is sounds like the heater core working correctly, did you get a chance to check the actuator?
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Sunday, January 5th, 2014 AT 8:37 AM
Tiny
RICHSTRUCK
  • MEMBER
No, I can hold on to both of them. Is there something that I can pour into the heater core to flush the dexcool that usually plugs the core?
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Monday, January 6th, 2014 AT 3:45 PM
Tiny
SATURNTECH9
  • EXPERT
Your not getting coolant circulation if both your upper and lower radiator hoses arent getting too hot to hold?I would address that maybe you got a bad thermostat?Did you put the thermostat in correctly?
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Monday, January 6th, 2014 AT 4:23 PM
Tiny
RICHSTRUCK
  • MEMBER
I changed out the actuator and now I have heat again! Thank you so much I has freezing. I love this site
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Sunday, January 12th, 2014 AT 5:45 AM
Tiny
SATURNTECH9
  • EXPERT
You welcome.
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Sunday, January 12th, 2014 AT 8:51 AM
Tiny
BRYAN2
  • MEMBER
  • 2003 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 75,000 MILES
My heat doesn't work until my engine overheats and the heat kicks on and cools my engine back to normal temperature.?
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Monday, November 12th, 2018 AT 5:21 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Try replacing the thermostat and make sure the heater core is not partially clogged-up don't work come on back.
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Monday, November 12th, 2018 AT 5:21 PM (Merged)
Tiny
NASCAR
  • MEMBER
  • 2003 CHEVROLET S-10CHEVROLET S-10
I have a 2003 S-10 ZR2, 85000 miles
when I frist start the truck I have little
heat coming out of dash vents, once I turn to the other vents I get cold air, and it stays that way on all vents.I have the heat all the way into the red, but still no heat. Not sure if I need a flush or new thermostat. Do you have any suggestions.
Thanks for any help. Rick.
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Monday, November 12th, 2018 AT 5:21 PM (Merged)
Tiny
NASCAR
  • MEMBER
The hose on the left of the heater core is
very hot, and the one on the right is cold.
Does this help at all.
Thanks for your time.
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Monday, November 12th, 2018 AT 5:21 PM (Merged)
Tiny
NASCAR
  • MEMBER
Ok I Got It Fixed Finaly.
I Just Did A Quick !0 Min Flush Job
On The Heater Core And Now I Have
Alot Of Heat. Amazing What A Flush Job
Can Do.
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Monday, November 12th, 2018 AT 5:21 PM (Merged)
Tiny
DRBOB
  • MEMBER
  • 2003 CHEVROLET S-10
  • 2WD
  • AUTOMATIC
I have a 2003 s10 the ac works fine and the blower is working and the engine is heating up but I'm getting no heat what should I look at?
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
Is the coolant full? WIth the engine hot, running, and the heater on, do both heater core hoses get hot?
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
WICKED360
  • MEMBER
  • 2003 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 60,000 MILES
My 03' Auto S-10 is at 60,000 Miles. I recently discovered (during the cold winter months) That the heat does not work. It only blows cold air. The fuses are fine, the heater core has no leakage or smoking (I have had 2 blown cores in the past and do not believe it is the problem), the AC unit works just fine. I am at a loss to what the problem may be. Any suggestions?
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
PEAR69
  • MEMBER
Your thermostat is probably stuck open. A thermostat works as follows. When you start your engine the coolant is cool. At this point the thermostat is closed, not allowing coolant to run through the radiator--where it is cooled. However your water pump is always pumping coolant somewhere, and regardless of whether the t. Stat open or closed, the coolant is usually flowing through the heater core and the engine. As the engine creates more heat the coolant heats up also. When the coolant reaches 185 degrees or so, the thermostat opens and allows coolant to flow through the radiator. As air passes through the fins of the radiator, the coolant is cooled down to safer levels for the engine. If the thermostat sticks open or fails open, the coolant will constantly flow through the radiator and be constantly cooled. This will not allow the coolant to heat up thus you are left in the cold. Your engine will be happy, but unless you like to be cold, you will not be happy.

BTW-- a thermostat can stick or fail closed which will cause over heating and eventualy engine failure, so have your thermostat checked and/or replaced. Let me know how you make out.
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
KINGRCR
  • MEMBER
  • 2003 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 48,000 MILES
I have a 2003 chevy s-10 with a 4.3 liter motor. My question is when I turn on the heat it blows cold air. The thermostat is working fine running about 190 degrees what do you think is causing this and what or how should I check it.
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
LEGITIMATE007
  • EXPERT
I think the thermostat is stuck closed and is not allowing the hot coolant to the heater core.
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
PAPAFRED
  • MEMBER
  • 2003 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 52,000 MILES
Fan works great. Coolant level is correct. All HVAC fuses are ok. Engine temperature correct. A/C works fine. When heater is turned on, nothing but very cool air comes out. Tried moving heater temperature control back and forth several times. Tried switching to different heater functions(floor, defrost, dash, etc.) Several times. Blows cool air in every setting.
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Monday, November 12th, 2018 AT 5:22 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Test the thermostat might stuck open and also the heater core if its clogged-up/coolant level
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Monday, November 12th, 2018 AT 5:22 PM (Merged)

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