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Old 01-05-2012, 10:08 PM   #1
Scooby Specialist
Member#: 148549
Join Date: May 2007
Chapter/Region: NESIC
Location: RI
95 RHD GC V7 STi
04 WRX, Sold the BlackSTi

Default HELP: When below ~35*F my heat just decides to turn cold whenever it feels like it.

Vehicle is a 2004 WRX Wagon


-The heat will not blow hot air until the car has been driving for more than 10 minutes, EVEN if the engine's temp is at the normal temp.

-Sometimes while driving the heat will randomly just start blowing colder air, in order to get it hot again I have to "play" with all of the switches again (turn temp from cold to hot and back a few times, turn fan on and off a few times, etc.).

-Sometimes it'll be blowing hot air and when I come to a stop light the rpm's will drop just a little, enough to notice it, and then the cold air comes.

-When it seems to be above 35*F-40*F it works fine, which is mostly during the day, then at night when it's really cold... it randomly decides to blow cold.

I have no idea what would cause this or how to troubleshoot the issue. I would greatly appreciate any info since it's very annoying problem to have. If anyone has any info that helps me figure it out than I'll send them a little something!

Thanks in advance.
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Last edited by HERSHEY; 01-05-2012 at 10:16 PM.
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Old 01-05-2012, 11:03 PM   #2
Scooby Guru
Member#: 70710
Join Date: Sep 2004
Chapter/Region: Tri-State
Location: Quakertown/AREA1320 391whp
2002 04STi Swaped RS
w/PPGS & 02 Wagon w/PPGs


Sounds like your coolant is low or you have a air pocket in the system.

Keep a jug of coolant in the car for a week and before you start the car when its cold top off the water box that feed the turbo. It will work the air out if any and fill the system up if low. Monitor the over flow tank and keep topping it off until its 1/2 full.
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Old 01-06-2012, 12:51 AM   #3
Scooby Specialist
Member#: 41762
Join Date: Aug 2003
Chapter/Region: International
Location: House of Pancakes
04 STi
in ur Floriduh


I noticed something similar when my water pump was first going out. I think the impeller was sometimes spinning (and circulating coolant to the heater core) but sometimes not.

I'm wondering if a malfunctioning thermostat (meaning it's staying closed) would block the flow to the heater core also. (not sure of the exact path of flow through the system without looking it up though)
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