Question about 2002 Nissan Sentra

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Heater blowing cold air

2005 nissan sentra blowing cold air. No leaks on floorboard, coolant level is ok and is clean, the air seems to have no heat at all in it. No indication of air pockets in system and no indication of engine overheating Just started looking into this. the heater blew some slightly warm air this morning on and off. My wife said the water temp guage was slightly cooler than normal.

I added a little bit of coolant last night, maybe 1/2 gallon. It still goes up to the top of the normal range of the temp guage, but not beyond. Then it goes back to just below normal.

I wonder if the thermostat went bad, and then the computer detected it and shut off the hot water to the heater core? After reading some of these questions I think the computer is involved somehow.

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  • ynneKG Dec 26, 2008

    My wife took it to a dealer garage, and they said it needs a new head gasket. This was apparently a problem with that year, and there are a lot of stories on the Internet about it. So I think I can accept their diagnosis.



    BTW, when adding coolant, this engine needs to have an air valve opened so that bubbles can escape.



    I assume they found some coolant on one of the plugs. So this is a job I can do myself, and while everything's apart, I will replace the belts and an idler. And maybe the timing chain tensioner.

  • ynneKG Nov 27, 2011

    So, it's been over a year, maybe two since I had this problem. It was a blown head gasket, and what was happening was exhaust gas was blowing through the leaking head gasket into the coolant, and those bubbles accumulated in the heater core. The simple test is to open the coolant reservoir and sniff for exhaust. It has a peculiar odor, not what you'd expect from a coolant reservoir. Also, you can test the coolant if you have that wherewithall.

    I could get it to blow hot by driving up a steep hill, and then within a minute, the bubbles would return to the core. Especially when the engine was at high rpms, it might run hot for a moment due to fast coolant flows, but the gas would quickly return.

    this is a problem with these sentras, it is a borderline lemon thing, in my opinion, but not bad enough to cause any kind of recall. I'll never buy a nissan again, unless i absolutely have to.

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My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!

Posted on Oct 16, 2009

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I am a nissan tech. The sentra and altima can be hard to burp all of the air from the cooling system. Depending on what engine that you have in the car, some of those nissans also have a water valve besides the main thermostat. They are very temperamental that there is a 50/50 coolant water mix. There is also a lot of head gasket issues that we have seen on those engines

Posted on Jan 29, 2015

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Just simply change the thermostat....I had the same problem and this is what I did and now it's hot as hell.

Posted on Dec 23, 2008

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My 98 nissan altima gxe hhas had this same problem and I have already replaced the thermostat but the water still isnt circulating and heater did work until the car overheated...There is no indiction that the water pump is bad...The temperature gauge stays on normal but the car is overheating

Posted on Jan 29, 2015

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My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!

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