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Discussion Starter · #1 · (Edited)
Hi, I have a 1997 328i and my heater is not working properly. The air blows out just fine and responds to the control panel but when I am in idle at say a stop light the heat stops coming and the air blowing is cold. It heats up again as soon as I start moving and the heat seems to work better if I am driving at faster speeds. Not so good for the drive to work with lots of traffic lights! Any suggestions as to what needs to be replaced or how I can fix it? Thanks

P.S...the car is not overheating and the air conditioner works fine. just the heat is a problem.


P.P.S...another site mentioned blower resistor problems with this kind of heat issue, does anyone know about blower resistors?

thanks!!
 

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Sounds like your thermostat is stuck open. How long does it take for your temperature gauge to get to the normal temperature (12 o'clock) position? It should only take a couple of minutes normally. If it's taking a long time that's pretty good confirmation of a stuck open thermostat.
The blower resistor is part of the speed control circuit. If your blower motor is putting out lots of air when set at the highest speed your resistor is OK.
 

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BMWCCA HPDE Instructor
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You could have a t-stat that is stuck open (as Don mentioned above), or you could be a bit low on coolant. My car had a stuck-open t-stat when I bought it. The HVAC would get warm enough for regular city driving though.

In my last car (a Nissan Maxima, but the same idea applies to any car), I once got low enough on coolant to prevent the heater from blowing hot air when idling at lights, but it wasn't low enough to overheat the engine. The air would heat up again once the light turned green and I got moving. In other words, I went through exactly what you are experiencing. Check to make sure your coolant is at the correct level (take your reading when the engine is cold).
 

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+1 to the t-stat.

as for the resistor, it is indicated by the fan not operating on lower speeds (current going through the resistor), but ok @ full (bypassing the resistor). most comonly one setting will fail, followed by additional settings.

at least so far. i haven't had a resistor fail at full speed on any vehicle to date. ymmv.



df
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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I don't think the resistors can fail at full speed, since full speed by-passes the resistors altogether. If it won't work at full speed the switch is bad or the blower motor is shot. Pray it's the switch.
 

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You guys are correct, I gave a backwards diagnostic on the resistor. Should have said if it's blowing air on the lowest speed it's probably OK.
 

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Discussion Starter · #7 ·
Thank you so much for all your replies! I flushed the coolant and am going to see how that works...if it keeps happening I am going to replace the thermostat. I asked at Pep Boys out of curiosity how much they would charge to replace my thermostat and they quoted me a price of around 300. Does anyone know if that seems to be a reasonable price (I have found them to be high before) or if replacing the thermostat is fairly easy on this year car? thanks again!

Cara
 

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BoostJunky
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Thank you so much for all your replies! I flushed the coolant and am going to see how that works...if it keeps happening I am going to replace the thermostat. I asked at Pep Boys out of curiosity how much they would charge to replace my thermostat and they quoted me a price of around 300. Does anyone know if that seems to be a reasonable price (I have found them to be high before) or if replacing the thermostat is fairly easy on this year car? thanks again!

Cara
Take some lube with you. Buy a new stat, new aluminum housing and do it yourself.

http://store.bimmerworld.com/aluminum-thermostat-housing-p38.aspx
 

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Yeah, just do it yourself and save hundreds. It's a very simple job.

Also, you never answered regarding whether or not your t-stat is actually stuck open. If it is, there are telltale sings. Does the temperature needle stay pegged at 12 o'clock after 5-10 minutes of driving? If not, your t-stat is stuck open. Once the car has been running for 5-10 minutes, the temp needle shouldn't move at all in either direction from the 12 o'clock position. If it is stuck open, you absolutely want to have it replaced, since not only will you not get hot air through the HVAC, but you will also damage your oxygen sensors (and possibly the catalytic converters, too) from running rich all the time.
 

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Discussion Starter · #11 ·
Hi,
I do believe my thermostat is stuck...It takes the temperature needle quite a while to get in the center position when started, even when it is warm out and of course, the heater isn't blowing hot air out when in idle. I added coolant...I was low on that and that seems to help a bit but I am still getting cool air when idling. While I was driving to get more coolant, I turned the defroster on and it started to overheat in idle and then dropped immediately to the 12 position once I started moving again, and that seems to have stopped with the new coolant. All it is doing is not blowing hot air in idle. My temp needle does not move from the 12 position now. As a side note, I do need to have the catalytic converter replaced but don't have the means to do that at the moment. I don't want to bring the car in for diagnostics because that costs so much so I am going to have to go by my best guess (from everyone's input). I obviously don't know a ton about cars but I am pretty handy and would like to replace the thermostat myself...for 30 bucks I figure why not and in this older car I am sure it can't hurt. Does anyone have any opinions on whether this still sounds like a stuck thermostat?

Thank you again everyone for taking the time to help. I am trying to learn all I can about my car so I can take care of it myself and not pay such overly expensive repairs!
 
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