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I drive a ’05 Nissan Sentra 1.8s with about 58,000 mi. on it. I’ve been having this ongoing heater issue for at least 3 years. It began back in ’08 when every time I came to a stop or the car was idling, the heat would go lukewarm/no heat. Once the car was moving again, the heat will go back to hot. When this first happened, I had the thermostat replaced and the issue seemed to be fixed.
Fast forward to ’10 the issue crept up again. This time a whole host of other issues crept up (rough idling, cylinder misfire, engine light on, low coolant). Turned out I had a blown head gasket, and I got that fixed (out of pocket). The dealer also did a coolant flush which I believe was the first one I had since I bought the car back in ’05. And they replaced the thermostat. A day later my car had no heat at all. Took it back to the dealership, they “burped” the system and it turned out there was air in the coolant system.
Now I have heat again, but it’s back to the original issue. While idling it goes to lukewarm/no heat. I have no idea what could be the cause or how to fix it.
It's time for a new one again. the cheep ones don't last very long or when they threw a blown head gasket situation.
Try a 195*F thermostat, spend the extra 2-3 bucks for the good one. They usually make them in a couple of different qualities, the cheep ones are junk and you could get one that sticks open right out of the box.
My guess is that there is at least some air or other gas in the system - with the engine turning cruising RPM, the water pump develops enough pressure to drive some water through the heater core, at idle, it does not.
Does this car have a coolant overflow "catch" can? One of the systems such that the radiator stays full of water with no air space at the top? If so, see if you have any air in the top of the radiator, if you do, probably the secondary seal on the radiator cap is not tight enough, typically, you fix that with a new radiator cap, although I have seen just cleaning the top of the radiator fill "spigot" and the cap's secondary gasket fix it.
I'm assuming the dealer put in a regular OEM thermostat of the correct temperature -
Worst case the head gasket problem is back. I have read about dealers changing a head gasket by taking the head with both manifolds still on it off, just change the gasket without surfacing the head, and put back together - not the highest quality repair. This is more typically seen on warrenty work where the profit margin is already slim.
It's time for a new one again. the cheep ones don't last very long or when they threw a blown head gasket situation.
Try a 195*F thermostat, spend the extra 2-3 bucks for the good one. They usually make them in a couple of different qualities, the cheep ones are junk and you could get one that sticks open right out of the box.
The dealer replaced the thermostat again when the head gasket was replaced and that was a week ago. But I'm not sure about the quality of the thermostat.
My guess is that there is at least some air or other gas in the system - with the engine turning cruising RPM, the water pump develops enough pressure to drive some water through the heater core, at idle, it does not.
Does this car have a coolant overflow "catch" can? One of the systems such that the radiator stays full of water with no air space at the top? If so, see if you have any air in the top of the radiator, if you do, probably the secondary seal on the radiator cap is not tight enough, typically, you fix that with a new radiator cap, although I have seen just cleaning the top of the radiator fill "spigot" and the cap's secondary gasket fix it.
I'm assuming the dealer put in a regular OEM thermostat of the correct temperature -
Worst case the head gasket problem is back. I have read about dealers changing a head gasket by taking the head with both manifolds still on it off, just change the gasket without surfacing the head, and put back together - not the highest quality repair. This is more typically seen on warrenty work where the profit margin is already slim.
I first thought it maybe air still in the system. Even after the dealer "burped" the system, but I was having this issue before the coolant flush and head gasket repair. Unless somehow air gets into the system overtime, I don't think air is the issue.
I do have a coolant reservoir and that is full. The label on the radiator cap says a highly pressurized system, so I'm not too keen on unscrewing that?
The head gasket was replaced a week ago, I don't think it could be back so soon? I have read of Sentra owners having a 2nd blown head gasket after the first one is repaired, so I assume there is more than one head gasket? The dealer explained to me that they sent the gasket head to another shop where they resurfaced it. This was out of warranty work ($1700 worth) so that might explain the thoroughness.
OK, it's possible they just need to burp the system again. The reason you had the problem before the head gasket was replaced is that some combustion (exhaust) gases were escaping through the leaking head gasket into the cooling system. Apparently this particular car has the heater core up higher than most of the rest of the coolant system, so any air or non-condensible gases accumulate there.
You should not take the radiator cap off when the radiator is hot, but once its cold, it simply unscrews like a jar lid, turn it to the left usually about 1/2 to 2/3 of a turn. What you are looking for is that the radiator should be completely full of water.
Need to be clear about cylinder head - the top part of the engine where the intake and exhaust manifold bolt to, cam or cams liven in there, and the valves - and the head gasket, the single metal and composition gasket that seals between the head and the engine block.
You could check the coolant level in the radiator when it's cold, but beyond that if the head gasket job was done only a week ago, just go back to the dealer and get them to check it again. If they are any good they will straighten things out for no additional charge.
I wouldn't put off going back to the dealer. At the very least they need to "burp" the system again.
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