Blowing hot air then cold?

"zeontestpilot" (zeontestpilot) 01/07/2017 at 07:23 • Filed to: Question

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Hey oppo, question for you guys. The heat in my car works, but seemingly random it blows out cold air for a while. Normally this wouldn’t bother me, but I have a three year old and a three month old; I’d like to keep them warm.

My car is a ‘07 Pontiac Grand Prix, and the thermostat was changed in the past few months. I talked to a mechanic friend, he said there is probably air in the cooling system. I just wanted to cover all my bases and ask oppo for their opinion as well.

It seems that the car doesn’t blow cold air when I first start it up; nor can I find any rhyme or reason to anything that makes the cold air start to blow. I’ve played with it for a while, and the hot air just comes back on when it does. Nothing seems to set it back on.

Currently, I’m thinking I need to bleed the air out of the system. If that’s what I need to do; is there anything I should know before I start? Thanks in advance.

Dash-doorhandle-6 cyl none the richer > zeontestpilot 01/07/2017 at 07:29

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got enough juice in the rad? heater core is high up, first place an air pocket will go in the cooling system

Flavien Vidal > zeontestpilot 01/07/2017 at 07:33

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Oil level is fine? No oil, no heater so...

zeontestpilot > Flavien Vidal 01/07/2017 at 07:34

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Oil is... or should be good.... I’ll check it out. Thanks for the suggestion.

zeontestpilot > Dash-doorhandle-6 cyl none the richer 01/07/2017 at 07:36

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Yeah, I’ll have to check that now. I didn’t even consider that (green car guy here. But hey, I’m showing interest and am trying!).

AndyG_UK > zeontestpilot 01/07/2017 at 07:50

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Air lock would be my first guess, does it have electronic climate control or manual heating, if it’s CC it could be a dodgy or blocked sensor maybe?

Berang > zeontestpilot 01/07/2017 at 07:51

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If you hear any gurgling from the engine or heater it’s got air in the cooling system, which means when the air bubbles go through the heater core you get no heat until more water comes through.

Flavien Vidal > zeontestpilot 01/07/2017 at 07:52

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Yeah it could lack a bit of oil, which would explain those sudden moments of cold (since it’s very cold outside) when you run without any...

Does it usually happen during corners or anytime?

That Bastard Kurtis - An Attempt to Standardize My Username Across Platforms > zeontestpilot 01/07/2017 at 07:54

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Sounds low on coolant. I just had that issue with my work van, I’d start it in the morning and it would come up to heat, but didn’t actually make any heat. Turns out I was down almost two gallons of coolant.

zeontestpilot > AndyG_UK 01/07/2017 at 07:55

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Honestly, not sure. Wasn’t aware there were two types, :/. I’m gonna guess the electronic one, since everything else is on the car.

zeontestpilot > Flavien Vidal 01/07/2017 at 07:56

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Definitely anytime. I’ll be driving then it happens. I prefer to have my feet warm (warm feet = quicker reaction time for me), and I notice the change instantly.

AndyG_UK > zeontestpilot 01/07/2017 at 07:57

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Do you set a temp and it keeps the car to that temp and also control the fan speed etc itself or do you just have a hot to cold dial and manually control the fan speed yourself, is there an “auto” button it?

RallyDarkstrike - Fan of 2-cyl FIATs, Eastern Bloc & Kei cars > zeontestpilot 01/07/2017 at 08:17

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Easy to tell if you have electronic climate control - is it 3 knobs (temp, fan speed, blowing location) ? If so, than it’s manual. If it’s one of those screens withe temperature you set with buttons, it’s electronic temp control.

zeontestpilot > Berang 01/07/2017 at 08:21

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Thanks, I’ll keep an ear open for the sound.

zeontestpilot > RallyDarkstrike - Fan of 2-cyl FIATs, Eastern Bloc & Kei cars 01/07/2017 at 08:22

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Manual for sure then.

zeontestpilot > AndyG_UK 01/07/2017 at 08:22

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It’s a manual then.

AndyG_UK > zeontestpilot 01/07/2017 at 08:36

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That makes it easier then, defo going to be something like air lock, low coolant, maybe a blocked heater core etc.

Flavien Vidal > zeontestpilot 01/07/2017 at 08:38

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Hum, may not be the oil then.... Check it out, just in case though. Could be massive bubble in the radiator too... But it should be moving fast enough so that you don’t feel it in the heater....

zeontestpilot > Flavien Vidal 01/07/2017 at 08:45

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Yeah, I’m planning on trying a lot of the easy suggestions here. Just waiting for it to get 10 degrees F first, lol.

zeontestpilot > AndyG_UK 01/07/2017 at 08:45

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How would I check those?

AndyG_UK > zeontestpilot 01/07/2017 at 08:51

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As someone has said before listen for a gurgling noise when the heat is turned on, that would point to an air lock for sure, you car should have a bleed valve to get the air out, normally takes a few goes. Low coolant is an easy check, just check the level in the header tank. A block can be more difficult but there will be an inlet and return pipe to the heater core in the engine bay going through the fire wall, they should both be pretty much the same temp when warmed up, if one is colder than the other you could have a blockage in the pipes or heater core, if it’s a minor block there are products you can put in your coolant to clear them out.

Busslayer > zeontestpilot 01/07/2017 at 09:07

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You could try burping the system. When the engine is cold, open the radiator cap. Check to see if it is full. If not, add some of the correct fluid. Then leave the radiator cap off and start the car. Let it idle for 20-30 minutes for any air to escape. It doesn’t hurt to get he front of the car up as high as possible (jack stads or ramps) so the open cap is higher than the heater core.

tpw_rules > zeontestpilot 01/07/2017 at 09:52

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Could also be messed up heater doors, which control the proportion of hot and cold air that gets to you. The control is manual but I seriously doubt the knob directly moves the doors in a car this new. Instead, there are electric or vacuum motors which move them and are directed by the climate electronics. Do you hear clunking or whooshing noises when you lose heat?

Dash-doorhandle-6 cyl none the richer > zeontestpilot 01/07/2017 at 10:09

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it’s what we’re here for, let us know what u find. It hit an honest -30 on my drive this mnorning.

zeontestpilot > tpw_rules 01/07/2017 at 10:28

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No noises, it just changes.