2004 3.4 Impala: Heat Then No Heat/Temp Gauge Up & Down??? - Chevy Impala Forums

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Old 12-14-2012, 12:15 PM   #1 (permalink)
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2004 3.4 Impala: Heat Then No Heat/Temp Gauge Up & Down???

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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Old 12-14-2012, 03:15 PM   #2 (permalink)
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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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Old 12-14-2012, 03:18 PM   #3 (permalink)
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Low coolant.

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Old 12-14-2012, 03:24 PM   #4 (permalink)
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Originally Posted by jrd0304 View Post
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?

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

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Old 12-14-2012, 03:28 PM   #5 (permalink)
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You really havent checked your coolant yet?

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Old 12-14-2012, 06:32 PM   #6 (permalink)
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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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Old 12-14-2012, 06:38 PM   #7 (permalink)
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Bleed the air from your coolant. There is a sticky here for the 3.4.

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Old 12-14-2012, 06:40 PM   #8 (permalink)
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I should mention that the symptoms you describe scream air pockets.

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Old 12-14-2012, 06:47 PM   #9 (permalink)
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Bleed the air from your coolant. There is a sticky here for the 3.4.
Link? I'm not seeing it and don't really know what I'm looking for...

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I should mention that the symptoms you describe scream air pockets.
Does this generally have any TERRIBLE effects on the wallet?

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Old 12-14-2012, 06:49 PM   #10 (permalink)
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It's free and takes about 15 minutes (that includes time to heat the engine). And the price of coolant, of course.

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Old 12-14-2012, 06:52 PM   #11 (permalink)
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http://www.impalaforums.com/diy-how-...tem-bleed.html

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Old 12-14-2012, 07:06 PM   #12 (permalink)
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As stated already... Bleed the sucker.

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Old 12-14-2012, 08:38 PM   #13 (permalink)
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Low coolant.
You told ME head gaskets lol. Looks like we were in the same boat OP, unless of course you smell gas fumes in the coolant reservoir...

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Old 12-14-2012, 08:48 PM   #14 (permalink)
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And did you figure out what it was?

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Old 12-15-2012, 05:51 AM   #15 (permalink)
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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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