Automotive

Cold Air blowing instead of Hot

  • Last Updated:
  • Jan 7th, 2012 2:44 am
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Jr. Member
Mar 4, 2008
132 posts
toronto

Cold Air blowing instead of Hot

Good Day guys
I never had this problem before and i recently started to experience it. When i am driving, warm/hot air is blowing depending what RPM i am at.
When i come to a stop sign or intersection. RPM drops and cold air starts to blow. it has never done this before. What do you think it can be ?

Thank you
Vehicle is 2008 mazda 6
20 replies
Deal Fanatic
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Apr 4, 2009
7664 posts
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North York
I also have a similar question.

The heating system in most cars ... use the engine heat, right? That is, there is no heating coil in most cars. (Is this assumption correct?)

Edit: I mean there is no electric heating coil like we have in our portable heaters at home.
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Dec 26, 2006
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Busybuyer888 wrote:
Jan 4th, 2012 12:26 pm
I also have a similar question.

The heating system in most cars ... use the engine heat, right? That is, there is no heating coil in most cars. (Is this assumption correct?)

Yes and no..

Basically as the engine heats up, the hot engine coolant is siphoned off if you will through basically a small radiator with a fan around it; I call it a heater core, but i don't know if that's the technical term.

The hot coolant heats up the core/coils, which then heats up the air as it passes over the core/coils..

The fan then blows the hot air into the cabin.

Sounds like OP's heater core is messed. It's a fairly big job to fix, as it's buried in/behind the dash most times.
The wonderous minds of some RFDers:
nx2k wrote:
Apr 13th, 2009 5:47 am
so let me get this straight
if you did the crime, you should do the time?
[OP]
Jr. Member
Mar 4, 2008
132 posts
toronto
Ebola wrote:
Jan 4th, 2012 12:40 pm
Yes and no..

Basically as the engine heats up, the hot engine coolant is siphoned off if you will through basically a small radiator with a fan around it; I call it a heater core, but i don't know if that's the technical term.

The hot coolant heats up the core/coils, which then heats up the air as it passes over the core/coils..

The fan then blows the hot air into the cabin.

Sounds like OP's heater core is messed. It's a fairly big job to fix, as it's buried in/behind the dash most times.
I hope its not. I had the car for 5 years now without a single problem. My friend told me to check the anti freeze levels. Can low level cause it to be cold and hot ?
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May 10, 2005
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Ottawa
Dixon007 wrote:
Jan 4th, 2012 12:57 pm
I hope its not. I had the car for 5 years now without a single problem. My friend told me to check the anti freeze levels. Can low level cause it to be cold and hot ?
Low coolant levels can cause this problem but I suspect you have something plugged or disconnected. Does it make any difference if you have the A/C selected or not? Does it make a difference if you have it in recirc or not?
What is the engine temperature? Is it warmer when standing still and cools as you drive? does it cycle warm and hot? Could be a sticking thermostat. Could also be a water pump impeller starting to go. If the impeller is corroding and bypassing water, it will not be properly pumped throughout the engine.
When was the last time you had the coolant replaced? It does have a lifespan. When you have it replaced, make sure they reverse flush the system and ensure they cycle the heater as well. It should cost around $100 (plus or minus). I would start with that.
It’s not how far you fall that counts. It’s how high you bounce that counts! General G Patton
Sr. Member
May 20, 2010
762 posts
68 upvotes
Not sure about your Mazda, but it's a somewhat common problem with 2nd Gen (2005-current) Nissan Frontiers. Air gets in the system, and it blows cold when idling, but warm when moving. Easy fix on the Frontier though - just over fill the coolant and it'll "burp" the system to get rid of air, and the extra coolant will drain out. Happened to me once 2 years ago, hasn't happened again yet.
Deal Addict
Dec 4, 2004
2014 posts
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It's usually a leak somewhere in the system that has allowed air to get in. Get the air out asap. It can lead to a blown head gasket. Most likely culprits for air into the system are (not necessarily in order or complete): cracked/faulty hoses, radiator, water pump, heater core, head gasket etc. "Internal" causes such as the heater core and the head gasket are a real PITA. I had a blown head gasket that was leaking internally. The coolant level kept going down and the temp gauge would bounce around and there was no evidence anywhere to find the source of the leak.
Member
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Aug 25, 2007
447 posts
104 upvotes
Toronto
Likely fluid level related, check the level and top it up and see if it corrects your problem. If it was just blowing cold air all the time then I would suspect a open thermostat, but you mentioned it was cold only at idle or sitting and not higher RPM's.
Newbie
Sep 27, 2009
89 posts
9 upvotes
+1 for heater core. Fords are notorious for this (well, older mustangs and first run flexes) and seeing that Ford and Mazda have shared components, I would not be surprised. The TSB on the flex is ridiculous for a similar issue.
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Apr 30, 2002
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jaydog4 wrote:
Jan 4th, 2012 5:57 pm
+1 for heater core. Fords are notorious for this (well, older mustangs and first run flexes) and seeing that Ford and Mazda have shared components, I would not be surprised. The TSB on the flex is ridiculous for a similar issue.
NO. All the Ford Fusions with similar issue (no heat on idle) were fixed by coolant fill and burp.
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Jan 2, 2009
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Red Deer
Lots of possibles here , what about the heater controller? Are they opening up the valves? All those controllers are electronic on these new vehicles, unlike the older vehicels where the controls were operated by cables.
Deal Addict
Feb 7, 2006
1233 posts
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as mentioned could be a bunch of things

check the coolant level, check for leaks, i had to replace the radiator on my minivan as it had several small holes
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