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Discussion Starter · #1 ·
2004 Impala 3.4 with about 170,000 miles goes from having normal heat to having no heat at all, and the dash temperature gauge goes up and down as well. The car doesn't boil over. I want to think it's the thermostat? This started since the temperature outside dropped, but I did have the same issue last winter as well. It vanished in the spring again.

What does everyone think? It's probably the head gasket, right?
 

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I would only suspect head gasket or lower intake gasket if you're actually losing coolant. Make sure you have enough coolant, and the coolant system is bled properly. If you don't lose any, then you're probably okay. If your coolant is low or you see a leak, then you already know what the problem might be.

If you're losing coolant, then you have a leak somewhere, you would have to look around and see where it's dripping, you'll see it on the ground or on/around the engine/under the dash by the heater core if its external, and if the oil is milky or you're burning coolant through the exhaust, then its internal. Sometimes the internal leak is so slow that the only way you'll find it is a leak down test. External could be anything, radiator, hose, lower intake, head gasket, water pump, heater core, therm gasket, inlet pipe, bleeding nipple, etc.

I've had my fair share of fun with these cooling systems. It could be a thermostat, which is really cheap, and easy to repair on a 3.4 if you take the throttle body off. If you take the throttle body off, it could take you less than a half hour. If you don't, I won't go there.

I've also had problems like this due to air in the cooling system, and I've also had no heat because of a bad radiator cap (enough pressure to cool the engine, but not enough pressure to blow through the heater core). I've wasted a lot of time and money chasing the gremlins, so the first thing I recommend you do is fill/bleed, then determine if there's a leak, and go from there. I got rid of my 2003 3.4 with 186K and every cooling system issue I had ended up being something cheap and stupid in the end, with the exception of the lower intake gaskets and even those aren't the end of the world. If you need any instructions about how to do any of this stuff just search the forum.

Good luck!
 

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Low coolant.
 

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Discussion Starter · #4 ·
I would only suspect head gasket or lower intake gasket if you're actually losing coolant. Make sure you have enough coolant, and the coolant system is bled properly. If you don't lose any, then you're probably okay. If your coolant is low or you see a leak, then you already know what the problem might be.

If you're losing coolant, then you have a leak somewhere, you would have to look around and see where it's dripping, you'll see it on the ground or on/around the engine/under the dash by the heater core if its external, and if the oil is milky or you're burning coolant through the exhaust, then its internal. Sometimes the internal leak is so slow that the only way you'll find it is a leak down test. External could be anything, radiator, hose, lower intake, head gasket, water pump, heater core, therm gasket, inlet pipe, bleeding nipple, etc.

I've had my fair share of fun with these cooling systems. It could be a thermostat, which is really cheap, and easy to repair on a 3.4 if you take the throttle body off. If you take the throttle body off, it could take you less than a half hour. If you don't, I won't go there.

I've also had problems like this due to air in the cooling system, and I've also had no heat because of a bad radiator cap (enough pressure to cool the engine, but not enough pressure to blow through the heater core). I've wasted a lot of time and money chasing the gremlins, so the first thing I recommend you do is fill/bleed, then determine if there's a leak, and go from there. I got rid of my 2003 3.4 with 186K and every cooling system issue I had ended up being something cheap and stupid in the end, with the exception of the lower intake gaskets.

Good luck!
Thanks for that. A friend has suggested the radiator cap, but another person has told me that he had the same problem with his Monte Carlo and they tore it apart and only solved the problem when they replaced the head gasket. That made me panic. The fact that I had the same problem last year when it was cold outside sorta confuses me though. If it were something massive like the head gasket, would the problem just vanish for so long?

Low coolant.
I'm not getting any warnings for low coolant. Am I missing something?
 

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Discussion Starter · #6 ·
Yeah, I have. It looked normal and I added a little to the reservoir just in case it was slightly down. Should I have done anything else? I notice that when I start the car up the temp gauge can go up to hot really fast. Way faster than it would seem possible to reach such high temperatures. And then it can suddenly drop way down again like nothing. Today I drove the car like this for an hour, and then another hour to get back home again, and aside from the constant temperature gauge and heater fluctuations, everything was otherwise fine. It's almost as if the car just isn't getting the info about how hot/cold it is under the hood...

Anything you all can think of is helpful as I can't get the car to a garage for a few days anyway.
 

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As stated already... Bleed the sucker.
 

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If you have a bad radiator cap, then the system pressure won't be sufficient to interact with the reservoir, and you also won't get a good bleed. If you end up going the thermostat route, grab a new cap, they're like 5 bucks. It's impossible to bleed the system completely without a good rad cap, and of course it's impossible to bleed the system completely if there's a significant leak somewhere. The thermostat won't work correctly either because there will be an insufficient flow above the waterpump. Are you getting a check engine light by the way? An outside chance that it's the coolant temp sensor if all else looks good? You won't necessarily get a warning for low coolant if the coolant is lower than where it needs to be. The fact that your issue only happens when it is cold out tells me that something in your system doesn't like temperatures below a certain point. Are you using orange DexCool equivalent antifreeze, and if so, has it ever been changed? When the engine is cold, does the upper rad hose collapse and go flat or does it stay relatively expanded? Is the radiator drawing from the reservoir? If the upper hose collapses, then you've got air and possibly lack of sufficient pressure.
 

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Discussion Starter · #16 ·
Thanks everyone for the advice. I'm gonna try get the car to a mechanic next weekend. I'll have everything checked and see what's going on. If it's some of the stuff you all said then GREAT! If it's the head gasket then... we'll see. It could be the end of the road.

Cheers!
 

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Why not take the 5 minutes and follow the steps in the link i gave you and save yourself a trip to the mechanic? Your problem is air pockets. They are easily bled out, even for someone who has no idea what they are doing.
 

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Worst case scenario, you get more air pockets because there is another problem causing them. As it stands, air is the issue.
 

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Discussion Starter · #19 ·
Update:

I took the car to a mechanic and the diagnosis was some form of head gasket leak, but apparently very small and not yet worth junking the car for. I don't plan to fix the car as it's not really worth it to me, but the guy told me to go to the dealer and ask for these tablets that you drop in the system, meant to stop the problem if it's not too extensive. They're cheap and about the size of a bottle cap. I put in 2 and the heat has been perfect ever since. Better than it's been for the past 2 months. I don't know how long it's going to last, but it's a fix for the time being, and I got a few more that I can pop in if it blows out again. The guy at the dealer told me that they sell loads and loads of these things and a lot of folks keep their cars running on 'em for years.
 

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Yeah, people put those things in and then yell about how dexcool supposedly ruined their cooling system, when really it's those damn tablets. Best thing you can do, flush the cooling system thoroughly to get that shit out, and replace the head gaskets. It's really not that tough of a job, and is affordable if you do it yourself.
 
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