# Intermittent heat on 2003 Nissan Altima 2.5L S



## onalandline (Oct 27, 2020)

Hello, my heat works intermittently. Sometimes it works right away. Sometimes it takes quite a while. Sometimes it seems to not come on. The engine warms up to normal operating temperature, and stays there. When I give it some gas while in park, I can sometimes hear the fluid circulating, which I assume is the fluid going through the heater core. Sometimes I do not hear it. Is it safe to assume it may be a bad, or going bad, heater control valve? Any input would be appreciated. Thank you.


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## onalandline (Oct 27, 2020)

Is there even a heater control valve on this model?


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## rogoman (Dec 16, 2004)

There's no coolant control valve. The temperature of the heated air is controlled by the "air mix door" inside the heater/cooling unit box. There's a cable running from the dash temp control down to the box. You can inspect where the cable connects to the "air mix door" to make sure it's properly connected. If you hear the coolant gurgling on and off, that seems to indicate air in the coolant system. If you're interested in purging the coolant system, here's a procedure:

Leave the radiator cap off; you'll have to drain some coolant to lower the coolant level first so that the coolant will not overflow from the filler neck of the radiator when it starts to warm up. Start your engine, and let it run until the system bleeds out air. It may take between 15 and 20 minutes for the engine to heat to the proper temperature and begin cycling coolant through. You'll observe the coolant level drop as the air is cycled out, and see air bubbles escaping from the radiator, and perhaps hear it gurgle; gradually add a little coolant at a time. You can also jack the front of your car up to help bleed the air from the cooling system. This puts your radiator higher than the rest of the cooling system and helps to bleed out the air pockets. Observe the temperature gauge as this is happening. The gauge should decrease to normal or close to normal.

After the system has cooled down, completely refill the radiator and the coolant reservoir again. The radiator may have been as much as half empty since earlier; it was simply air that made it seem full.


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## onalandline (Oct 27, 2020)

rogoman said:


> There's no coolant control valve. The temperature of the heated air is controlled by the "air mix door" inside the heater/cooling unit box. There's a cable running from the dash temp control down to the box. You can inspect where the cable connects to the "air mix door" to make sure it's properly connected. If you hear the coolant gurgling on and off, that seems to indicate air in the coolant system. If you're interested in purging the coolant system, here's a procedure:
> 
> Leave the radiator cap off; you'll have to drain some coolant to lower the coolant level first so that the coolant will not overflow from the filler neck of the radiator when it starts to warm up. Start your engine, and let it run until the system bleeds out air. It may take between 15 and 20 minutes for the engine to heat to the proper temperature and begin cycling coolant through. You'll observe the coolant level drop as the air is cycled out, and see air bubbles escaping from the radiator, and perhaps hear it gurgle; gradually add a little coolant at a time. You can also jack the front of your car up to help bleed the air from the cooling system. This puts your radiator higher than the rest of the cooling system and helps to bleed out the air pockets. Observe the temperature gauge as this is happening. The gauge should decrease to normal or close to normal.
> 
> After the system has cooled down, completely refill the radiator and the coolant reservoir again. The radiator may have been as much as half empty since earlier; it was simply air that made it seem full.


Sounds like an inexpensive, easy attempt at correcting the problem, so I'll give it a try. Thanks for the reply. I'll get back to you.


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## onalandline (Oct 27, 2020)

Well, I followed your instructions on bleeding air, and added maybe 1/3 bottle of antifreeze 50/50 premix to the system. The heat seems to be working now. Thanks for your help, and saving me time and money! I just wonder where the antifreeze went since there are no visible leaks.


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## onalandline (Oct 27, 2020)

BTW, is there a way to flush the entire system, including the heater core, without having to access the tubes that go through the firewall?


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## rogoman (Dec 16, 2004)

onalandline said:


> BTW, is there a way to flush the entire system, including the heater core, without having to access the tubes that go through the firewall?


The easiest way is to first remove the filler cap on the radiator, then place a drain pan under the radiator where the drain valve is located. Open the drain valve. Make sure the car is level; *not jacked up*. That should drain the entire system including the heater core. Also drain the overflow expansion tank if need be.


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