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Hey Guys. I have a 2004 Silverado Z-71 5.3L with right at 40K miles. I live in Nebraska and it's FREEZING here, -15F this morning. My heater has started malfunctioning here over the last few days. At idle the heater blows cold air, but when I'm driving it'll blow hot. So, I can't start the pickup and let it warm or defrost the windows, and I never drive far enough for it to even warm the cab between the stops in traffic. The thermostat is not sticking and the engine warms to a nice toasty 210; right in perfect operating range. Like I said it does blow hot while I'm driving. It's got to be a sensor or something. Any ideas guys?

 

Thanks in advance for the help,

Jade

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Hey Guys. I have a 2004 Silverado Z-71 5.3L with right at 40K miles. I live in Nebraska and it's FREEZING here, -15F this morning. My heater has started malfunctioning here over the last few days. At idle the heater blows cold air, but when I'm driving it'll blow hot. So, I can't start the pickup and let it warm or defrost the windows, and I never drive far enough for it to even warm the cab between the stops in traffic. The thermostat is not sticking and the engine warms to a nice toasty 210; right in perfect operating range. Like I said it does blow hot while I'm driving. It's got to be a sensor or something. Any ideas guys?

 

Thanks in advance for the help,

Jade

 

Hello Jade,

 

Assuming the fan is working properly, have you checked the coolant level?

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Hey Guys. I have a 2004 Silverado Z-71 5.3L with right at 40K miles. I live in Nebraska and it's FREEZING here, -15F this morning. My heater has started malfunctioning here over the last few days. At idle the heater blows cold air, but when I'm driving it'll blow hot. So, I can't start the pickup and let it warm or defrost the windows, and I never drive far enough for it to even warm the cab between the stops in traffic. The thermostat is not sticking and the engine warms to a nice toasty 210; right in perfect operating range. Like I said it does blow hot while I'm driving. It's got to be a sensor or something. Any ideas guys?

 

Thanks in advance for the help,

Jade

 

Hello Jade,

 

Assuming the fan is working properly, have you checked the coolant level?

 

 

:thumbs:

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The coolant level is good. I just topped everything off last week while doing an oil change. I checked it again yesterday when I noticed it was acting up too. One thing I did notice this morning though. After letting it run for about 15mins I went out to leave and the temp was up about 250. As soon as I revved it just a little it immediately dropped down around 200. Now I'm thinking the thermastat is either sticking slightly or the coolant might not have a good mix for these cold temps.

 

Sidenote...I tried to take the kiddos to school this morning and couldn't keep the window thawed long enough to see where the hell I was going. I'd squirt the old de-icer on 'er and as soon as the wipers would stop it would freeze back to a nice thin sheet of ice. It's to damn cold to be messing with since I don't have a heated shop. So I drove it down to my local shop. I'll let you guys know the verdict.

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When is the last time you did a flush? I'd flush the heater core thoroughly, change the 'stat. Also hoses of course if it's time.

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My heater started that this morning same as yours sat in yard running for 10 min got in and was cold!!! :thumbs: no heat going down road all sudden heater is working :D will check it out when i get off work. Bellman let us know what shop said.

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The old lady's Impala is having this problem too. It was low on coolant, so I put more in it last night. She told me this morning that she didn't really have any heat. Granted it was -18° outside, but I'm wondering if a coolant flush isn't a good idea.

 

Keep us updated :thumbs:

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Shop said they let it run off and on several different times. Sometimes it would warm close to overheating and sometimes it wouldn't warm at all. Verdict = Finnicky thermostat with a poor coolant/water mix. Sometimes it sticks open and sometimes it sticks closed. They said that the minus 30 windchills have been causing a lot of peoples coolant to slush up and wreak havoc on the stats.

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I'm having a similar problem in 04. My heater doesn't work at all though. The past two weeks I'll be going down the road and I'll get a short blast and then no heat after that. I'm right under 210 on the temp gauage.

 

I also have no defrost. It seems if I select defrost it blows out at the feet.

 

In my research I could have a blend door problem.

 

When Justin did my tune I noticed I had history of B0263 and B3770. With a current B0408 and B0414.

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$131 later got me a new stat, full flush, and a nice toasty cab. A pretty simple job that would've probably taken an average Joe a couple or four hours to do on a Saturday. But, with these temps out it was well worth it for me to pay the shop to do it. They're good people that I've used several times over the last couple of years anyway. i don't mind giving them a little light work occasionally.

 

Thanks for all the help guys.

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