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1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold


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kjburns128
New User

Mar 3, 2014, 1:05 PM

Post #1 of 10 (1791 views)
  post locked   1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

1998 Chevy Malibu, 3.1, 125k

We had just replaced the lower intake manifold gasket (common issue on this model car) and after we got everything backed together the car ran great, however, the heat would be hot then cold and alternate between the two. Honestly, it is pretty random fluctuations between the two. We replaced the coolant in the system with the gasket repair (did not do a flush), replaced the thermostat, bled the coolant line to get rid of any possible air bubbles and the issue is has not gone away. Best guess is heater core is plugged (checked both lines running into the heater core and one was hot and the other was luke-warm). Just odd that it would blow hot then cold which would mean the heater core is plugged then unplugged and back to plugged again. Any advice is greatly appreciated.


kev2
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Mar 3, 2014, 1:35 PM

Post #2 of 10 (1780 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

  first thoughts
Air in system - purge and purge agan-
Thermostat- you used a 195 degree AC DELCO ?
The core being restricted - very common on GM this era -thank you Dexcool - Flushing and BACK flushing the core often solved the problem. BUT I would ask how did it perform BEFORE the work?

unlikely but have to ask - were any hoses removed - replaced correctly?

http://www.youtube.com/watch?v=ad9u8jADrvU


(This post was edited by kev2 on Mar 3, 2014, 1:39 PM)


kjburns128
New User

Mar 3, 2014, 1:58 PM

Post #3 of 10 (1775 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

The new thermostat is not AC Delco but is a 195 degree thermostat.

The heater worked perfectly fine before repair.

We have done multiple purges (probably 5-7) and the problem is still there.

Also, all hoses that were removed for the gasket repair were replaced correctly.

Have to try the flushing of the heater core. Just something you don't want to get into when you don't have anywhere good to drain the water after it comes out.

Any possibility it is the heater blend door actuator?


kev2
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Mar 3, 2014, 2:38 PM

Post #4 of 10 (1771 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

the reason I asked how it operated BEFORE was to eliminate those items blend door, waterpump, heater core blockage.
It worked before so I would concentrate on - air, T'stat, and lastly blockage.

the air temp door actuator is electric - not prone to moving like the vac type. Is the system changing modes ie defrost-dash -floor ?


Hammer Time
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Mar 3, 2014, 2:45 PM

Post #5 of 10 (1768 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

This engine is very difficult to get all the air out. I generally vacuum fill them to get it out. You still have air pockets.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



kjburns128
New User

Mar 3, 2014, 3:08 PM

Post #6 of 10 (1761 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

Yes, you can change the change the modes the heater. All the options on the dial work properly.


Discretesignals
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Mar 3, 2014, 5:21 PM

Post #7 of 10 (1757 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

You should reverse flush the heat core. If you have a blockage, you'll have a hard time getting air out of the system.





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Hammer Time
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Mar 3, 2014, 5:25 PM

Post #8 of 10 (1753 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

The heater worked great before so it doesn't look like the core is plugged up. The motor still has air pockets and you need to get that resolved ASAP or you're going to do some serious damage.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



kjburns128
New User

Mar 4, 2014, 7:06 PM

Post #9 of 10 (1718 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

It took some doing but we were finally able to get all of the air pockets out of the system. Heater is back to working the way it should. Thanks to everyone for their help!


Hammer Time
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Mar 4, 2014, 7:13 PM

Post #10 of 10 (1717 views)
  post locked   Re: 1998 Chevy Malibu, 3.1, Heater blows hot air then goes cold  

Glad you resolved the issue.

Question closed as solved now.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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