YACT: Heater only works when car is moving

[Doggiedog]

My slowly deteriorating 95 BMW 325i has been having some AC/heater problems lately.

Anyone know why the heater only works when the car is moving? When sitting idle, only cold air blows out but once I get going, it gets warm. If I stop at a light it gets cold again.

 

[flamingelephant]

does it have an aluminum block?

 

[Thegonagle]

Did you check your coolant level?

If it's already full, then you may need to bleed the system of air. (Most cars a bleeder nipple near the thermostat.)

 

[speed01]

Second on checking the coolant level.. If it's low, there may not be enough to pump at low rpms but when you drive the rpms go up and it manages to pump through.

Speed

 

[jemcam]

Originally posted by: speed01
Second on checking the coolant level.. If it's low, there may not be enough to pump at low rpms but when you drive the rpms go up and it manages to pump through.

Speed

An air bubble in the cooling system will cause this problem. After you fill the cooling system if it's low, make sure to check it again for a couple of days on a regular basis because the air may burp out of the system into the tank, causing what appears to be a significant drop after the first drive after refilling. Keep it topped off and monitor the coolant level for a few days to be sure you don't have a leak.

 

[KC5AV]

I concur. I had low coolant in my truck last year, and it wouldn't work if I wasn't moving. Add some water/coolant to the reservoir and you should know in just a few minutes.

 

[Delleet]

Have you check the coo...oh...

 

[Specop 007]

Hell, if its cold (20 or less or so) my car will actually cool down at idle. A full stop light will cause me to lose nearly 1 full tick on the temp gauge.
Which really sucks in stop and go traffic.

 

[Syringer]

Coolant?

 

[arcenite]

Some people above are telling you to check the coolant, but for the wrong reasons. The waterpump is powered by a belt which is turned by the motor. At idle, the pump is not pumping as much fluid through as it would be while the engine is at higher rpms. While coolant level may be possible, if your coolant was that low you'd be having other problems as well. If you are not noticing any coolant leaks, something may be clogged up between the pump and the heater core. If you are noticing leaks, I think that heater core would be the first thing to look at.

Bill

Edit: Also, there really would be no reason for the coolant system to have to be bled either, unless the coolant system was recently flushed (or flushed before the problem occured)

 

[Megatomic]

Originally posted by: aRCeNiTe
Some people above are telling you to check the coolant, but for the wrong reasons. The waterpump is powered by a belt which is turned by the motor. At idle, the pump is not pumping as much fluid through as it would be while the engine is at higher rpms. While coolant level may be possible, if your coolant was that low you'd be having other problems as well. If you are not noticing any coolant leaks, something may be clogged up between the pump and the heater core. If you are noticing leaks, I think that heater core would be the first thing to look at.

Bill

Edit: Also, there really would be no reason for the coolant system to have to be bled either, unless the coolant system was recently flushed (or flushed before the problem occured)

Interesting, this is the exact condition my wife's car is in. Her cooling system was completely flushed and refilled and now the heat is only hot when the car is moving. I'll check on the radiator to see if it has a gas bubble as suggested.

Thanks guys.

 

[Doggiedog]

Thanks for all the replies.

You are all correct. I do get a check coolant error on my computer. Even when I fill the coolant up I still get the error.

I did have my water pump and radiator replaced about 10K miles ago and had them flush the coolant. I will check it out again.

Thanks for the great replies!

 

[arcenite]

Originally posted by: Doggiedog
Thanks for all the replies.

You are all correct. I do get a check coolant error on my computer. Even when I fill the coolant up I still get the error.

I did have my water pump and radiator replaced about 10K miles ago and had them flush the coolant. I will check it out again.

Thanks for the great replies!

If you get a check coolant error when the coolant is low, make sure you keep coolant in it. The reason your coolant would be going down after being filled is because air still has to be burped out. Keep on top of that. Now if your coolant light stays on even when it's been full (for say... a day [to rule out error])... You may need a new sensor.

 

[Doggiedog]

Originally posted by: aRCeNiTe

Originally posted by: Doggiedog
Thanks for all the replies.

You are all correct. I do get a check coolant error on my computer. Even when I fill the coolant up I still get the error.

I did have my water pump and radiator replaced about 10K miles ago and had them flush the coolant. I will check it out again.

Thanks for the great replies!

If you get a check coolant error when the coolant is low, make sure you keep coolant in it. The reason your coolant would be going down after being filled is because air still has to be burped out. Keep on top of that. Now if your coolant light stays on even when it's been full (for say... a day [to rule out error])... You may need a new sensor.

The coolant error is always on. When I fill it, I can only put in a tiny bit before it overflows. There aren't any leaks as far as I can tell.

How much is a new sensor? If I need to put any more money into this car, I'm putting it to pasture. Actually, I will be getting rid of it before June when inspection time comes up.

 

[CraigRT]

Might also want to keep an eye on the coolant level, if it keeps going down on a regular basis, you could either have a leak, or a bad gasket (head gasket) that would suck.

 

[speed01]

Originally posted by: aRCeNiTe
Some people above are telling you to check the coolant, but for the wrong reasons. The waterpump is powered by a belt which is turned by the motor. At idle, the pump is not pumping as much fluid through as it would be while the engine is at higher rpms. While coolant level may be possible, if your coolant was that low you'd be having other problems as well. If you are not noticing any coolant leaks, something may be clogged up between the pump and the heater core. If you are noticing leaks, I think that heater core would be the first thing to look at.

Bill

Edit: Also, there really would be no reason for the coolant system to have to be bled either, unless the coolant system was recently flushed (or flushed before the problem occured)

I don't think checking the coolant level to make sure it's correct can exactly be called a wrong reason. At idle the water pump should be able to pump an adequate amount of coolant through entire cooling system to heat the car and cool the engine. The fact that it's running off of a belt is irrelevant since it does heat up at higher rpms so the belt is obviously working. And, they wouldn't necessarily have other problems if the coolant level was that low as it does tend to evaporate, but it also could be a leak. Although, if the coolant level is correct, I would also suspect a blockage in the system or a faulty water pump. And, if the heater core were leaking, chances are you would notice a sweet sort of odor inside the car as most heater cores are up under the dash I believe.

Speed

 

[arcenite]

Originally posted by: Doggiedog

Originally posted by: aRCeNiTe

Originally posted by: Doggiedog
Thanks for all the replies.

You are all correct. I do get a check coolant error on my computer. Even when I fill the coolant up I still get the error.

I did have my water pump and radiator replaced about 10K miles ago and had them flush the coolant. I will check it out again.

Thanks for the great replies!

If you get a check coolant error when the coolant is low, make sure you keep coolant in it. The reason your coolant would be going down after being filled is because air still has to be burped out. Keep on top of that. Now if your coolant light stays on even when it's been full (for say... a day [to rule out error])... You may need a new sensor.

The coolant error is always on. When I fill it, I can only put in a tiny bit before it overflows. There aren't any leaks as far as I can tell.

How much is a new sensor? If I need to put any more money into this car, I'm putting it to pasture. Actually, I will be getting rid of it before June when inspection time comes up.

Don't rule out the coolant yet until your heat works. If you add coolant (hot), run your car for a day, then the next day your coolant is low again after driving (hot) it's still burping somewhere. To get a price on a sensor, just call up advance or something and get a price. Though if the coolant light started coming on as soon as you started noticing the heat problem, it's not the sensor (not yet anyway)

 

[arcenite]

Originally posted by: speed01

Originally posted by: aRCeNiTe
Some people above are telling you to check the coolant, but for the wrong reasons. The waterpump is powered by a belt which is turned by the motor. At idle, the pump is not pumping as much fluid through as it would be while the engine is at higher rpms. While coolant level may be possible, if your coolant was that low you'd be having other problems as well. If you are not noticing any coolant leaks, something may be clogged up between the pump and the heater core. If you are noticing leaks, I think that heater core would be the first thing to look at.

Bill

Edit: Also, there really would be no reason for the coolant system to have to be bled either, unless the coolant system was recently flushed (or flushed before the problem occured)

I don't think checking the coolant level to make sure it's correct can exactly be called a wrong reason. At idle the water pump should be able to pump an adequate amount of coolant through entire cooling system to heat the car and cool the engine. The fact that it's running off of a belt is irrelevant since it does heat up at higher rpms so the belt is obviously working. And, they wouldn't necessarily have other problems if the coolant level was that low as it does tend to evaporate, but it also could be a leak. Although, if the coolant level is correct, I would also suspect a blockage in the system or a faulty water pump. And, if the heater core were leaking, chances are you would notice a sweet sort of odor inside the car as most heater cores are up under the dash I believe.

Speed

Sorry if it seems like I was trying to insult someone, I wasn't. I agree with everything else that you said though. Only reason I mentioned the belt was to explain why the pump pumps less at idle.

Bill

 

[nwfsnake]

Good news! Not sure what your problem is, but you local BMW dealer will be happy
to fix it for only $1750!

 

[arcenite]

Originally posted by: nwfsnake
Good news! Not sure what your problem is, but you local BMW dealer will be happy
to fix it for only $1750!

That's just to look at it

 

[DainBramaged]

Originally posted by: Thegonagle
Did you check your coolant level?

If it's already full, then you may need to bleed the system of air. (Most cars a bleeder nipple near the thermostat.)

*heh* Nipple *heh*

Sorry...

 

[arcenite]

Originally posted by: DainBramaged

Originally posted by: Thegonagle
Did you check your coolant level?

If it's already full, then you may need to bleed the system of air. (Most cars a bleeder nipple near the thermostat.)

*heh* Nipple *heh*

Sorry...

Might want to get your Dain examined

 

[Doggiedog]

Let me backtrack perhaps.

About 7 months ago my radiator went at 92K miles. I understand this is very normal for BMWs as they use plastic radiators. I got it fixed by an acquaintance who is a head mechanic at a BMW dealership. He replaced the radiator, water pump, flushed the coolant and changed the thermostat.

I didn't notice a problem with the car until winter hit. The coolant light is always on now but the temperature is normal. It takes a very long time for the heat to come out. I'd say at least 15 minutes.

I took it to a rip-off BMW repair shop (the acquaintance is too far away) and he said I have a serious issue from just my explanation. Since this car is literally falling apart on me (ABS is gone also), I'm not looking to invest more money in it because it likely won't pass inspection. If it is something like bleeding the coolant, I may take it in but if its something serious, I may just hold out. From everyone's explanations, it doesn't sound as bad as the repair guy said.

FWIW, when my radiator went, I did drive the car with the temp gauge way in the red several times. Most of the time, it wasn't for longer than 15 mins. I don't think I damaged the engine since the mechanic didn't find any problems with it. Just from listening, the engine sounds great.

 

[sao123]

did u ever consider that maybe your heater core is blocked?

u replaced nearly every part in your coolant system except it.

I had that happen to an old chevy of mine. It would be cold until i was moving, then be warm, then back to cold at a stop. What was happening, is the water pump was ever able to pump some hot coolant into the heater core during higher rpms, but not at lower.

Heater cores are not real expensive, but can be a B1TCH to change, depending on how much stuff u have to take out to get to it.