# 01 Sentra Overheating



## Mike1121 (Nov 21, 2014)

Hey all, 

I have an 01 Sentra that overheats after about 5-10 minutes of driving. Initially, the heat works fine in the car and the temp hovers around normal. However the heat eventually will start blowing cool air. A couple minutes after this happens the temperature will start to climb. If you get out of the car and pop the hood at this point you can see the overflow tank for the coolant start to fill up with boiling coolant. After letting the car sit for 10-15 minutes the coolant in the overflow tank will drain back into the radiator.

I have checked the thermostat and it seems to be working fine (I heated up some water to make sure it opened up). The water pump is not frozen but I haven't managed to take it off to look inside. I am trying to flush the radiator right now with vinegar. Additionally, I unhooked the hoses from the heater core and ran water through it and that does not seem to be clogged. 

This car has had bars head gasket sealer used on it about 15,000 miles ago.

Is there anything obvious I can try that I am missing? 

Thanks for reading.


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## smj999smj (Jan 1, 2006)

Head gaskets are a common failure on these cars. A cylinder leakdown test would confirm that. I don't recommend Bars Leak as it does gum things up; if a head gasket is bad, the only way to fix it is to replace it.


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## Mike1121 (Nov 21, 2014)

I don't think the head gasket is the problem. It isn't exhibiting any symptoms of a blown head gasket (white smoke out of exhaust, radiator chop when starting, etc.). Additionally when the Bars was added, the car was running and driving, it would just misfire a little when starting up. The Bars stopped that from happening. It is not misfiring now when I start it up.


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## smj999smj (Jan 1, 2006)

The Bars Leak may have partially sealed a small, leaking area of the head gasket, which corrected the noticeable misfire; but at higher speeds there is more pressure in the combustion chamber and this could be enough pressure to push combustion gases past the gasket and into the coolant jacket, causing it to overheat (as well as an air pocket in the heater core, which would explain why there is a loss of heat). White smoke would only occur if the coolant enters a combustion chamber; it's entirely possible that the leak is such that it allows pressurized combustion gases to escape, but let little or no coolant into the combustion chamber...or at least not enough to create a noticeable amount of steam (or "white smoke"). Also, there would have to be a very large leak in the head gasket to cause what you refer to as "radiator chop."
If the water pump was frozen, you would know because the belt wouldn't be able to turn it, resulting in a squeal or throwing off or breaking the drive belt. Other than locking up, water pumps usually fail in one of two ways: the shaft bearing fails, resulting in noticeable pulley wobble and/or noise, or, it leaks, which would be visibly obvious. Some people mention the possibility of the of the impeller corroding and not pushing the coolant, but these instances are extremely rare with today's long-life coolants. 
If your radiator is not clogged, I would put my money on a bad head gasket, especially if this happens to be a 1.8L. Again, a cylinder leakdown test would confirm this. So would a chemical analysis of the coolant for signs of hydrocarbons. You'll also want to make sure your electric fans are working.


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## Mike1121 (Nov 21, 2014)

Alright, that makes sense. Thanks for the quick reply and bearing with my lack of knowledge. I think I was a little in denial about the head gasket.


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## smj999smj (Jan 1, 2006)

Well, it's understandable. Nobody wants the labor or expense of taking the head off of the engine. If it turns out to be the problem, make sure you have a machine shop check the head for cracks and resurface the deck for a good, clean surface for the gasket to seal.


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