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post #1 of 4 Old 11-12-2011, 06:38 AM Thread Starter
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Heater blowing cold air...sometimes!?

So I'm driving home from work the other day, and stop at the drive-thru for some coffee. I happen to glance down at the EVIC, and it's showing a temp of 230 and climbing - quick! It's never gone past 220 even in 110 degree weather stuck in gridlock the A/C on full. The outside temp was about 32 at the time. So I cranked the heat up full, and got cold air...great. At this point, I've got my coffee (so at least I'm getting some heat...lol!), and the temp's at 240. I turned the fan off completely, and turned it back on, and got some serious hot air, and the temp started coming back down, plus I'm also moving as well being out of the line up. The temp stabilized at about 200, with the heat still cranked. Needless to say it was a WARM drive home! Turned the heat off at one point on my drive, and the temp started to climb, and came back down when I turned the heat back on. So broken t-stat, no biggie, right? Replaced the old one, no problems - ran the car for a bit, no leaks, call it a day. Coolant was a tad below min, but the gasket around the old t-stat was pretty mangled, and figured I may have lost a bit from that.

I left for work this morning (outside temp approx 30), and when the engine temperature reached about 175, I turned the heat on (just to get it up to temp quicker), and I'm getting cold air...temp gets up to 200-205, and I'm still only getting mildly warm air, not the usual blast of heat. Then the temp dips back down to 175, and fluctuates for the next 20 min between 175-205, only getting slightly warm air at best. When I merged on to the divided hwy, I sped up from 60 to 75, and presto! Instant heat blast, and the engine temp stabilizes at 200. If I turn the heat down in the cabin, then I'm back to cool air. I'm only getting heat if I have it cranked up full. The coffee at this point has gone from keeping me warm to keeping me awake...lol!

So I'm thinking water pump? Heater core? Heater core valve? IR cabin sensor? All of the above? None of the above?

Any help/insight you guys can provide would be much appreciated. Many thanks.

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post #2 of 4 Old 04-19-2012, 08:58 AM
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Did you ever get this resolved? Mine is doing the exact same thing. I replaced the t-stat as the rubber on it (not the gasket) was torn. The coolant was a little low so I topped it off, but still the heat fluctuates from hot to cold. I noticed a little "moisture" in the bottom of the fan shroud, but I don't know if maybe i spilled a little antifreeze when topping it off or if I have a leak. Gonna dry it off and keep an eye on it. Thanx in advance!

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post #3 of 4 Old 04-19-2012, 04:25 PM
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Sounds like air-loc in your cooling system,If you didnt open up bleeder when refilling coolant can cause this problem.Run your engine with the heater on,when it gets to normal temp,shut if off,let it set awhile and check your overflow tank.Also make sure coolant cap is good.Make sure your fans are working right.
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post #4 of 4 Old 04-19-2012, 06:03 PM
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Going through this with mine, turns out it is the HVAC Blend Door that is broken. Sometimes this is caused by the temperature controls being out of sync with the blend door. Not in my case. Cost $200 for the dealer to diagnose by taking lower access panel off the HVAC to see the blend door was broken. Some other people have had issues with the blend door actuators/motors... here is a link to a diagram of the parts in the HVAC The blend door is the half dome shape that sort of looks like a shield from a pilot's helmet. Oh Dealer only wants about $1100 to remove and replace that part.


With your temperature fluctuations, maybe you have a combination of cooling system and HVAC system problems.

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