I have a 1996 Legacy Wagon and when driving, the heater works perfect but when I idle, it blows out warm air. Once I start moving again, the heat comes out hot. Antifreeze is at the proper solution and is full. Should I flush the radiator or do you think it's the thermostat?
I have had a similar situation myself and it was my heater core, on my vehicle it was a very time consuming job as i had to remove the entire dash to get to it. What you could try first if not tooo bad . Flush the system and reverse the hoses on the heater core and reverse flush. You can drive reversed for short time with the heater core hoses reversed as i did for over a week it may un plug if not as bad as mine was....Plenty of how tos on u tube to reverse flush your heater core and system.. I replaced my heater core radiator and water pump and a vent was broken in the dash i found and bad vacuum lines. a couple actuators were bad. had no heat to floor after doing all that it roasts me out of the truck, and the vents work properly including blowing on my feet the way i prefer.... Hopefully this helps you
SOURCE: '90 Subaru Legacy overheating....
cool air and overheating point to low coolant level. Do you have a bleeder valve near the thermostat? You may have air trapped in the system. If no air trapped, the radiator may be plugged up not allowing proper circulation of coolant.
SOURCE: 2002 subaru legacy heater not working
heater core could be plugged,try removing both heater hoses to core and back flush
SOURCE: OVERHEATING!!!!
Since you changed your waterpump, you need to do an air bleed...
This is INSANELY important!
The airbleed is mounted on the top of the radiator on the passenger side.
Its made of plastic, has a seal, and looks like a 1/2 inch (12mm) philips screw head.
To do this, make sure the engine is cold and not running.
Use a large FLAT HEAD screw driver and turn it counter clockwise.
It might be very tight, so be prepared for a bit of torque to turn it!
Unscrew it, and look in the hole.
Coolant should be at the top of the bottom of the screw hole.
It should be low, so add coolant to the open hole.
While doing this, be sure the radiator cap is off so you can balance the fluid level properly.
Why do you need to bleed the system?
The engine has a slight tilt upwards toward the radiator, and both your waterpump, and block will have a tendancy to leave air near the top of the block and heads.
This is a common mistake on several makes after a coolant change.
Make sure all fluids are topped off, fill the overflow tank to its max level indicated on the tank itself and your done.
Provided you havent been driving long on the car in this condition, it shouldnt blow a headgasket.
A good way to know if the headgasket is bad is the radiator cap will have a brownish "slime" indicating combustion gasses are getting into the cooling system.
IF this is the case, your engine is pumping combustion gasses into your system and no amount of air bleeding with help.
Another tell tale sign of coolant being pressurized, is a overflowing "overflow" tank, and a sudden blast from Normal operating temprature to HOT, and then suddenly.. it goes back to Normal again.
There is usually a "gurgling" sound under your dash..
Lets assume you just need to do an air bleed, and things will go back to normal.
Also, if your airbleed screw has alittle coolant leaking around it, replace it with a new one as the seal and plastic have worn due to age.
Good luck!
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