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N52 coolant & bleeding woes

Discuss problems you have had or are having with your Z4
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GTwice
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N52 coolant & bleeding woes

Post by GTwice » Fri Apr 09, 2021 11:24 am

I have a 2007 3.0si, with the N52. The car is pretty much new to me, I bought it in January and then immediately went to work with stuff, among others I did OFHG and coolant flush.
When doing that, I was never fully satisfied with the coolant bleeding results - I would often hear bubbles of air going through the heater after engine shutdown, and doing multiple bleeding procedures in the row I would still hear some air around the engine with the second or third cycle. Also occasionally I get a 2E83 (Electric coolant pump, power-reduced operation) at startup, which apparently could indicate air in the cooling system - the pump was replaced last year.

Anyway, since then I drove about 2000 miles, and yesterday the low coolant light came on, but then disappeared and appeared again a few times on my way home (temperature was good). I bought some antifreeze and wanted to refill today in the morning, but the coolant level is still at maximum - about 10-15cm below filler neck, just touching the float bracket. It was however even higher after initial refill and bleed, so I guess I have a minor leak, but with almost 200k miles on the clock I am not too worried, at least the engine oil is clear with no sludge at all.
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One more thing I've noticed - even after not driving it for a few days, the cooling system stays pressurized - when I try to open the expansion tank cap, some air and coolant escapes, which surprises me, because I would expect air only - after all, the liquid is at the bottom, right?

Now I'm not sure if I should do anything about the situation? Why would I get low coolant light if the level is right? Could there still be some air trapped after 5 or more bleeding procedures?
Is it safe to add coolant above the max level to silence the low level warning light?
Is it normal for the system to remain pressurized for multiple days and spew some coolant instead of just air when opened?
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N52 coolant & bleeding woes

Post by enuff_zed » Fri Apr 09, 2021 11:51 am

I believe I am right in saying that the low coolant light is triggered by the float shown in your photo sinking to the bottom and actuating the switch at the bottom of the expansion tank?
It could be that air in the system is making it sink as that air arrives at the expansion tank?
It could be a sticky float?
If the level is a little lower than when you first filled it, that would indicate that some air has escaped and the water level dropped a bit.
If you still have pressure after a few days then I'd say there's very little chance you have a leak of any kind.
Have you tried running it for a while with the filler cap off? That may release a little more air?
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N52 coolant & bleeding woes

Post by ph001 » Fri Apr 09, 2021 11:18 pm

What procedure are you using to bleed it?
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N52 coolant & bleeding woes

Post by GTwice » Sat Apr 10, 2021 12:12 pm

The one from TIS: ignition on, blower on low, max temp, AUTO on A/C panel, and then you press accelerator for 10s or just trigger from INPA (I did it both ways)
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N52 coolant & bleeding woes

Post by ph001 » Sat Apr 10, 2021 4:04 pm

That is the correct procedure. Can you park your car at a steep angle or put the front wheels up on ramps and repeat the process? Then do the same with the arse end up in the air. That usually sorts it.
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N52 coolant & bleeding woes

Post by GTwice » Tue Apr 13, 2021 6:56 pm

Unfortunately I just moved and don't have a garage anymore or any spot to wrench really. I'll have to come up with something.
On today's ride I think I've noticed that I get a low coolant lamp when the heater is on, after lowering the cabin temp. or just switching of the blower (so the full A/C system) the light disappeared - might be a problem with the heater core?
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N52 coolant & bleeding woes

Post by ph001 » Tue Apr 13, 2021 7:17 pm

GTwice wrote: Tue Apr 13, 2021 6:56 pm Unfortunately I just moved and don't have a garage anymore or any spot to wrench really. I'll have to come up with something.
On today's ride I think I've noticed that I get a low coolant lamp when the heater is on, after lowering the cabin temp. or just switching of the blower (so the full A/C system) the light disappeared - might be a problem with the heater core?
It’s not unheard of to get air locks around the heater core. I would go find a steep hill to park on and repeat the bleed procedure.
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N52 coolant & bleeding woes

Post by Patchkabel » Wed Aug 18, 2021 11:34 pm

Hi,

did you resolve your problem?
I have the same fault on my car like you described.

Thx
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N52 coolant & bleeding woes

Post by GTwice » Thu Aug 19, 2021 8:13 am

Not really. I have a small coolant leak somewhere, but it's so minor that I just occasionally top the coolant to keep the level high enough to avoid any lights on the dash.
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N52 coolant & bleeding woes

Post by colb » Thu Aug 19, 2021 9:50 am

Shame you have no garage and access to a compressor, I invested in a vaccum coolant filler to get over the air trapped in the heater matrix, used it on a 1.9 and it worked very well, only had a few air bubbles after the fill via the bleed screw.
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N52 coolant & bleeding woes

Post by GTwice » Thu Aug 19, 2021 9:55 am

Yeah, it's a shame, I'm used to having a lift in my garage and being able to do everything...
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N52 coolant & bleeding woes

Post by enuff_zed » Thu Aug 19, 2021 10:01 am

enuff_zed wrote: Fri Apr 09, 2021 11:51 am I believe I am right in saying that the low coolant light is triggered by the float shown in your photo sinking to the bottom and actuating the switch at the bottom of the expansion tank?
It could be that air in the system is making it sink as that air arrives at the expansion tank?
It could be a sticky float?
If the level is a little lower than when you first filled it, that would indicate that some air has escaped and the water level dropped a bit.
If you still have pressure after a few days then I'd say there's very little chance you have a leak of any kind.
Have you tried running it for a while with the filler cap off? That may release a little more air?
Following further investigation, which involved another member close to me (Ratcatcher) cutting open my old tank, it seems the float you can see is there purely for visual reference and has no bearing on the low level warning light. This is operated by another float, trapped in the bottom half of the tank, which has a magnet in it. It curves around the low level sensor, which in fact is fitted into a recess in the bottom of the tank, but does not intrude into the coolant itself (so you can swap it without getting wet)
When the level falls, initially the visual float drops down. This stops around 2/3 of the way down the tank.
If the level falls further it allows the magnetic float to fall, which actuates a reed switch in the sensor, putting on the low level light.

I know it doesn't solve the issue, but I had to correct my initial hypothesis.
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N52 coolant & bleeding woes

Post by Patchkabel » Sun Sep 05, 2021 11:43 am

Just want to update you:

I run the coolant bleeding procedure four times. Each time i could add some coolant of about 250ml.
In the end there was about 1 litre missing. Before every bleeding the expansion tank showed full level.

The fifth run didnt change anything. For now the car runs fine with heater on or off. On the first run you could clearly hear the air in the hoses.

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N52 coolant & bleeding woes

Post by GTwice » Thu Sep 23, 2021 5:59 pm

An update from my side as well: a few weeks ago my coolant leak got worse, had to add some after almost every trip to work. The shop replaced the expansion tank, coolant leak stopped completely, no more problems with bleeding as well. So, the conclusion - if you have problems with bleeding the cooling system, first fix all the leaks, even minor ones.
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N52 coolant & bleeding woes

Post by Z4Mariner » Tue Apr 11, 2023 4:12 am

Calling up an older thread to add my "+1" to the advice to put the front up on ramps for bleeding.

I replaced much of my Z4's cooling system about six weeks back with the car level, on jack stands. Thus began my saga of auto-bleeding coolant, thinking things were fine, finding the coolant was low, topping up, and auto-bleeding again. Five times so far, and I hope I've got it now. I kept looking for leaks, but I think now that it's just a problem with trapped air. The last of my five auto-bleed cycles was done with the front of the car on ramps, and it ran for over twenty minutes with no leaks visible. I will check it again tomorrow before driving again.

If I were to do it over, I'd start with the car on ramps !
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