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So my wife has a 2003 Nissan altima, and it wont blow heat anymore, It blows heat but not at idle unless you press the gas and let the engine rev, even at normal operating temp it still does not blow heat, I checked and there is heat when you drive it above 50mph, which is weird I do not know the problem. I know it is not a G8 related question, but I don't know where else to turn...

The head basically doesn't work the A/C does but i'm not sure what the problem is? I was thinking low on coolant but I filled it up cause it was a little low but that still didn't help. I am thinking it could be the heater core being clogged? I am not for sure, but I do know that the two tubes that lead into the fire wall I checked, the in tube was hot the outgoing tube for the heater core was not it was barely warm? So I don't know, hope you guys can help thanks !
 

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Have you checked all the heater core lines? you could have a clog. i'd flush it and then check it out.
 

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Low Coolant. There is a leak somewhere. If you don't see any in the engine compartment, then it is in the motor (Fingers crossed that it is not).

As the pump impeller spins more slowly under lower RPMs, an air bubble propagates inside the heatercore as it is normally on a bypass line and on the higher side of the loop. Under throttle, higher RPMs restore flow through the heater core to overcome the air bubble. It will also suck the overflow reservoir dry.

Adding coolant will temporarily solve the problem, but the leak must be found. Look for sticky residue when the motor is cool. Or if it has totally evaporated the glycol, look for a white residue near hose connections.

First, I would direct your attention to the radiator cap, and go from there.
 

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Discussion Starter #4
Low Coolant. There is a leak somewhere. If you don't see any in the engine compartment, then it is in the motor (Fingers crossed that it is not).

As the pump impeller spins more slowly under lower RPMs, an air bubble propagates inside the heatercore as it is normally on a bypass line and on the higher side of the loop. Under throttle, higher RPMs restore flow through the heater core to overcome the air bubble. It will also suck the overflow reservoir dry.

Adding coolant will temporarily solve the problem, but the leak must be found. Look for sticky residue when the motor is cool. Or if it has totally evaporated the glycol, look for a white residue near hose connections.

First, I would direct your attention to the radiator cap, and go from there.
There is no leak to be found, Just don't know still, I am thinking it is the lines one of them is hot when both are supposed to be the one on the right is hot and the other one is not. The car never overheats so I don't know lol? I will try a flush.
 

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To me it reads like the heater core has plugged up a bunch. The symptoms you describe, was very much like the way my old 96 Chevy SS acted. Somehow the chemicals/compounds that went into the finished GM product called DEX-COOL, would breakdown over time and cause the liquid to turn into a pasty pink sludge (only seem to happen in that heater core). Over a period of 13 years, I had to *twice* disconnect the in an out rubber hose's going towards the firewall. Then using a garden hose flowing water at a low flow rate along with a towel wrapped an squeezed around it (to keep the water going where I wanted/needed it to go), slowly flush/purge that pink pasty substance from all of the heater core tubes. Once done, the heat output was now more powerful than you would ever need. Both hoses were now very hot to the touch, indicating excellent coolant flow. Based on the touch feel you state, It dosen't sound like the heater shutter door (within the HVAC unit) has a problem.
 

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Mine didn't overheat, either. The coolant temps stayed right about where they always were. When stopping at a red light suddenly it was lukewarm. I get going again and it was red hot.

When it cooled I opened up the radiator cap and it was empty of coolant up top. It had some coolant in it, but by and large it was drawing coolant from the overflow reservoir when running and it would still retain enough coolant in the system.

Try a flush, but first when cool get the radiator cap off and take a look.
 

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Since the car is not overheating nor presumably exhibiting signs of getting hotter than usual then it rules out a few other possibilities unless the ambient outdoor temperature is relatively cool... say like in Alaska. A little low as in you merely topped it off or low but not bone dry? Depending on how low the coolant was increases the likelihood of an air pocket/bubble developing. Am unfamiliar with Nissan's, but do they put coolant bleeder valves on their vehicles? As stated above, would either flush the entire cooling system or just the heater core. Flushing the entire cooling system removes a larger quantity of sediment than merely doing the heater core. Auto parts stores sell chemical flushes which, in theory, should clean anywhere anti-freeze travels. However, I am unfamiliar with chemical flushes and typically flush the engine/block, radiator, and heater core with a water hose turned on near bout medium-high. Arguably, chemical flushes are more beneficial, thorough, and longer lasting than the garden hose method. To flush the heater core with a garden hose. Remove both hoses from the pipes on the firewall. Turn the water on (not full blast) and run it both ways (alternating pipes) until the water is crystal clear mentally notating its original color when initially flushed. Reconnect both hoses and give it a whirl. This thread might be relocated to the lounge section of the forum by the moderators.
 

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Back flush the heater core
 
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