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lazydog76, Chevy Technician
Category: Chevy
Satisfied Customers: 203
Experience:  10 years exp professional, ase master, gm tech
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How to replace a heater core in a 2001 Blazer S10 4WD 4door

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How to replace a heater core in a 2001 Blazer S10 4WD 4door LT? I just replaced the thermostat…still have cool air blowing through the vent.

Hi, i will assist you in your problem

what is the temp running on the temp gauge. is the top radiator hose and heater hoses getting hot.

Customer: replied 8 years ago.
Temp stays at just shy of 210. I had it in the shop which the guy said if it isn't the thermostat it is the heater core...So the cheaper 1st fix was the thermostat...just got it back and I still have cool air blowing.
ok, first lets check to make sure that the heater hoses that attatch to the engine and to the heater core are hot or very warm to touch, there are 2 hoses lets make sure that you check them both.
Customer: replied 8 years ago.
You will have to give me a moment to start the truck and get it is 10 degrees here in WI...and I have been researching online for a bit and the truck has been off. I take it that the two hoses at the top of the engine that go into the firewall of the truck cabin are the hoses to check? pretty good with a wrench but no expert when it comes to this part of the truck. Smile thanks for the help thus far.
wow 10 deg, its 60 here in alabama, but yes the hoses are 2 black hoses that are attached on the passenger side of the engine and run to the firewall.
Customer: replied 8 years ago. I need bet!!! OK the hose close to the passanger door is hot and the the hose toward the driver side is cool...not cold...but very cool.

ok , if one is hot and the other is cold, this is a stopped up heater core, this is a very common thing. flushing out would give you heat probly for the remainder of the season but it will stop up again.

let the engine cool down and take the lines off of the engine and place a garden hose in the hose closest to the drivers side and turn on the water, this will back flush the heater core. reassemble and make sure to top off the antifreeze.


or remove the dash assy to gain access to the hvac box and remove and replace the heater core.


also i recommend to flush the cooling system and refill with 50/50 antifreeze and water mix.

Customer: replied 8 years ago.


Wow...that is it!!! Thanks!!! I am a bit pissed at the shop I go to then. I asked them to take the first step in fixing this...which we agreed the thermostat was step 1 $100.


If that did not take care of it then step 2 heater core at $1,000. There was no mention of step 1.5...flush the system. This just saved me big step was to dump this POS and buy a new truck $30,000...was not looking forward to that!!!


I was looking online at Auto Zone...I see part number 394195 new heater core for $ that the part I need?


Other problems I have with this truck which I have received help is the Wheel Bearings in the front, the dumb oil lines that are seeping, and a low voltage on the alternator.

im not sure on the autozone part number but they should have it in stock. WOW 1000 dollars is a lot of money for heater core replacement, i would find another shop to do my work.
lazydog76 and 5 other Chevy Specialists are ready to help you
Customer: replied 8 years ago. last question...I never flushed my coolant before...I am sure it is easy but could you walk me through it?

sure, purchase coolant flush at a local parts store, and 2 gallons of antifreeze. drain the radiator fluid into a container, the drain is located at the bottom of the rad. on the drivers side.

refill the system with the cleaner and water, run the engine till hot and make sure the rad is full of water, follow directions on the flush container as to how long to run engine.

then after this process drain again.

refill with water only and repeat the same process as above except don't add any more cleaner, do this until the system is clear.

then drain once more and then refill with 1 gallon of antifreeze and then top off with 50/50 antifreeze.



most flush cleaners will have a step by step directions on the container.

Customer: replied 8 years ago.
Do I add anything to the reservoir? or will the 50/50 mix fill as needed from the overrun? I know...sounds dumb...

yes add the 50/50 mix to the res. and also be careful because the engine will be hot after running, be sure to let cool to a safe working temp. before opening the cap or drain plug.