No heat at idle

[dwm]

You can see part of it at the bottom of this picture from my oil pressure sender installation:

[EGS]

Open small bleed screw next to overflow tank cap. "

Is this 'bleed screw' obvious or can someone post a picture? Sorry to ask but I didn't receive my repair manual yet and I'd like to bleed the system ASAP.

Thanks!

[Randy Forbes]

Is this 'bleed screw' obvious or can someone post a picture? Sorry to ask but I didn't receive my repair manual yet and I'd like to bleed the system ASAP.

Thanks!

It's pretty obvious; looks like you could use a quarter ($.25) to open it.

[Z3SpdDmn]

Guys, there is another possibility other than air stuck in the heater core. But first, if air IS stuck in there, you need to run the hell out of the engine for a bit. It will eventually work its way out. Start with a cool (not cold, though) engine and rev the hell out of it up and down with the heat on full blast until it goes hot. You'll proabably feel it be sporatic and then eventually get consistantly hot.

The other possibility is that your thermostat is stuck open. If your water pump failed, your engine would OVERHEAT (especially if you had an early plastic impeller let go). I assume you all know this, but when the engine is running lightly, not producing a lot of heat, it normally will close the thermostat so that water does not circulate through the engine/radiator, but then open when it needs to get the temp down. If just circulation alone isn't cooling it enough, then it will run the fan. If you're moving it generally won't run the fan. If you're idling and its real hot and the engine fan isn't enough, it'll engage the electric A/C auxilary fan also. Common knowledge, I think.

Fortunately, on our cars, when our thermostats fail, they stick open, not closed. So our cars overCOOL rather than overheat. No danger to the car. Mine has just failed for the second time. I replaced it 4-5 years ago for the same problem. No heat when the engine is running lightly and light heat even when its running on the highway. Just replace the thermostat and while you're at it, replace the housing with an aluminum housing if you haven't already.

[2kredz3]

I know this thread is from about a year ago but just wondering if anyone has any new input or advice? My car does the same thing........... heater blows hot when cruising down the highway but when I stop and the engine is idle it immediatley starts blowing cold. After reading all of the previous post, it looks like it could the thermostat stuck open or in need of a coolant flush/bleed. Anyone have any other thoughts or a guess on which of the possible culprits it is most likely to be?

my vote is for air in the coolant system. what does the temp gauge do when this happens? is it ever high or low?

[2kredz3]

air bubble for sure. if the tstat was sticking the gauge would be going crazy.

[Austin2u]

Thanks 2Kredz3! I will see if I can figure out how to get rid of that bubble

[MJFX328]

Ya if the tstat was gone the needle would go crazy.

[Austin2u]

I found this suggestion for getting rid of the air. Do you think it works?

"It is rare that you will get an air pocket, but it does happen. When it does I will let the vehicle sit over night with the radiator cap and bleed screw out and it will "burp" itself.

[MJFX328]

Hummm.. Just dont forget to put it back on. Dunno if its worth doing

[ZZZING]

air bubble for sure. if the tstat was sticking the gauge would be going crazy.

When my thermostat was bad ( stuck open ) the temp gauge did not go crazy, it just read lower than the 1/2 way mark. I bought a scangauge II to keep an eye on it until I could replace cooling system parts, and it read about 165 degrees on the highway, after replacement it reads 207 degrees- but the temp gauge is right dead in the middle.

[deka1951]

In the steps to bleeding the cooling system, can you explain the reason for turning the key to the on position and not starting engine? I have seen that in other threads and never understood that step of the process. Thanks

[curtnc]

Electric motor running when cold. I always wondered what that sound was coming from

[325m3bimmer]

Test drove the car, 99 M Roadster, to verify the heater still has same problem that the water pump didn't fix. Heres what I have, at idle heater blows very cold air, at about 2000 rpms while driving the heater blows very hot air, at 3000 rpms the heater blows extremely hot air, stop for a red light and within 10 seconds the heater is blowing extremely cold air. I can't see how the heater core could be blocked with it blowing such hot air at 3000 rpms. What am I missing?

Like u read my mind. Exact same problem. I had a new thermo and water pump put in. But also still no heat at idle, rev to 2-3k then good got heat. I think it's air in the system. Need to bleed it. Anyone agree?

[rf900rkw]

It is low on coolant.

[deni2s]

I have the same issue in US spec 2.8 1997 z3. But someone installed small coolant radiator, probably from 1.8 engine, so that might be my cause of problem.

I found those suggestions as primary cause:

1) air in the system
2) because earlier models didn't had secondary pump which eliminates this problem, so that's how it's supposed to be
3) failing water pump
4) low on coolant

[rf900rkw]

As far as I know, no Z3 came with the latent heat system. Certainly not the US spec cars. So there is no secondary pump.

Also, I argue that 1 and 4 are the same thing. Too much air means not enough coolant. There is a lot of mystique and hookus pookus generated about "air in the system". It's not magic. If there is air, it's because you didn't fill the system completely/correctly.

[deni2s]

Randy, can you please explain me if that's the expected behaviour I have?

The thing is I bought us spec 1997 2.8 car, and it has small coolant radiator, probably from 1.8 (it's smaller and overfill tank is on the other side than on stock 2.8). Someone just repaired something on low budget. Car runs fine, at least during autumn/winter - no overheating, coolant temp arrow always in the middle, but it warms much faster than stock 2.8. Coolant is not leaking and stays at the same level when cold. The problem is, that this level is on the bottom of overfill tank And if I fill it full, coolant is overfilling when warm until it's level is again at the bottom. At first I was afraid that coolant goes inside the head, so tried to fill a few times, but now I see that's not an issue and I am driving daily a few months and coolant level stays the same. Only that it's blowing cold air at idle. So that might be ok, right? I plan to install matching radiator probably on summer, but if car runs fine, I can delay those expenses.

[resistro]

I got the same issues with my X3 (E83, 3.0L). Not a lot of heat until I rev the engine high. Replace thermostat (TWICE), the heat control valve, and coolant temp sensor. BLED the heck out of the system multiple times in multiple ways. Still same issues. I can feel the both heater core hoses are hot, so I think it's flowing, but enough? I think my next step is replace the electric water pump or try and flush out the heater core.

[SteveG66]

sounds like you need to bleed the system, I've read that on multiple occasions on this site, that should free up your issue.

[Licensed Monkey]

Problem resolved- Air in the coolant system.
Sorry for bumping this old post. I joined this site just to answer this issue, as it seems no one came back with a conclusive resolution.

I replaced the composite coolant pipes beneath the intake manifold, but after bleeding the coolant system by every suggested means (factory manual, countless educational threads, and even some crappy Utube vids) still had no heat from Cabin Vents at idle. Took 3 days of checking the level in the coolant reservoir each morning once the engine was completely cold. Each time it was empty, and I would top it off and open the bleeder valve to check for air. Seems the system will 'burp' itself upon cooling down. Now have heat in the Cabin at idle once again.

Some notes on what I tried in bleeding the system:
As per Service Manual- Key in 'On' position with Heater set to highest setting (to fully open Heater Control Valve), with Coolant Reservoir Cap off and Bleeder Screw opened.
As per some useful online advice- Elevate front of vehicle before attempting Service Manual procedure; rev engine several times up to at least 3K with engine at running temperature (with Coolant Reservoir Cap off and Bleeder Screw closed); 'Pump/Squeeze' Lower Radiator (with Engine OFF) while bleeding system.

All of this works to some extent, but the design of the Heating System appears to keep air in the Heater Core (likely due to the elevation of the Heater Core in relation to the lower position of the Heater Control Valve). In my case none of it worked to get all the air out. It figures that as soon as I got heat from the Cabin Vents the car tossed me the pesky P1622 code for the Thermostat, but at least I know now what to expect after cracking the Coolant System open again... patience... along with a jug of 50/50 and a Screw Driver for at least 3 mornings after I complete the repair.

Some footnotes to all the suggested considerations regarding this issue of 'No Heat at Idle'...
-A failed (or failing) Water Pump would cause Engine Overheating long before lose of heat in the Cabin Vents
-A failed and stuck open Thermostat would cause the Engine to run cooler that it should (as well as effect other systems in Engine Management), but the most that would happen with the Climate Control in the Cabin would be less heat, but not a total lose of heat.
-A failed Heater Control Valve could cause a total lose of heat in the Cabin, but it would have to be stuck (or failed) in a closed position to do so. More often this valve would fail in an open position, and allow hot Coolant to enter the Heater Core while attempting to use the Air Conditioning System.

Hope this helps!

[mpire]

Air bubble is the reason anytime you have hot air when moving and then no hot air when stopped.

[Vintage42]

The heater core receives coolant from the head through the connector pipe under the manifold.
I think that lack of cabin heat at idle is caused by low coolant that fails to fill the head until the RPM of the water pump is raised.
Bubble is an innocuous term for low coolant that could overheat the head without showing on the temperature gauge.

[CuriousGeorge15]

I have the same problem. I start my car, the engine warms up, but it's still blowing cold air. This morning I actually used my wipers to clear my windshield and bits of snow started coming out of my vents. After 100 yards or so of driving, it starts to blow warm air.

Did anyone ever get resolution to this?

My symptoms were similar at idle my car would blow cold air but at rev or while driving it would blow hot air, my battery lost its charge because the terminals came loose and I had to retighten the terminals and I also discovered that my tensioner bracket for my alternator had came loose and had enough play to lose charge on my alternator this was due to the tensioner nut shearing off the teeth on one side I turned it to the other side that could still lock onto the bracket teeth for a quick fix until I could get the parts in and ordered a new bracket, tensioner nut and alt belt and now the problem is fixed. 89’ 325ix

[BimmerBreaker]

I think that lack of cabin heat at idle is caused by low coolant that fails to fill the head until the RPM of the water pump is raised.

No coolant at the head at operating temp means a ruined engine