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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 01-17-2014, 02:42 PM   #1
Sigrid7993
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Intermitant low coolant light, possible air in system?

Shorter version:
About 18 months ago, (the summer of 2012), I replaced the cooling system on my '01 330i. After successfully bleeding the system with a gallon of bmw spec coolant & a gallon distilled water I then had a problem free car until the end of that Winter (approx. February/March of 2013), when the low coolant light (yellow coolant light which is in the lower left quadrant of lights) would intermittently turn on for as little as 30 seconds or as long as 4-5 minutes.

The engine temperature would never elevate, and the low coolant light would always turn off, although it would sometimes cycle on/off as much as 2 or 3 times over a longer drive. There have never been any check engine lights.

During this time I tried bleeding the system (never noticed any air, just coolant leaking from the bleeder valve on the top hose). Upon checking the coolant level when the system is cold, the red stick has always floated between a finger or two above the expansion tank's cap.

The problem then completely went away during the summer of '13, (from May '13 to October '13) which I can only assume means there is air hiding in the heating system.

Now over the last 4 months this intermittent low coolant light has returned. Symptoms haven't changed, and the coolant level when cold always appears within spec.

Questions:
Am I looking at a faulty sensor? Do I more likely have an air bubble hiding out inside the cooling system? The coolant looks clean, and there is no indication of missing coolant, or that crystallized white percipient coolant leaves behind when there is a minor radiator or hose leak.

Extra Information:
This included (I believe) just about everything that pertains to the system:
- Waterpump with composite (not plastic) impeller, gaskets
- Waterpump Pully
- Thermostat
- Two drive belts
- New radiator
- Expansion tank
- Upper/Lower Radiator hoses
- New Fanswitch & Coolant level sensor
- Along with the assorted gaskets and clips that came with the kit.
- Gallon of BMW spec coolant
- Gallon of Distilled h20

I followed the bleeding procedure, Turn ACC ON, put heat to 90f (to flush coolant thru the heater valve). I first added the entire gallon of bmw spec coolant, and then began adding the distilled water. It took a while to get it so the bleeder valve (ontop of one of the hoses), to leak a constant stream of coolant w/o bubbling air but after 10 minutes or so it worked.
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Old 01-17-2014, 03:16 PM   #2
TurnersInOz
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Could be the sensor, or possibly the ET.
It has been seen where low quality ET's can cause this. What kit did you use?
You can also try swapping the sensor on the ET with the one on your washer fluid tank to see if the issue goes away.
Also, you say that you saw coolant leaking from the bleeder screw. Was this actually leaking, or were you referring to when you tried to bleed the system?
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Old 01-17-2014, 03:34 PM   #3
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If it's been working OK for awhile, and the coolant level is OK, I'd be inclined to second the expansion tank sensor. They run around $15 from a discounting BMW sponsor (I checked TheBMWPartStore.com)
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Old 01-17-2014, 04:13 PM   #4
Sigrid7993
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Quote:
Originally Posted by TurnersInOz View Post
Could be the sensor, or possibly the ET.
It has been seen where low quality ET's can cause this. What kit did you use?
I'm pretty sure I purchased the level 2 cooling kit from ECS (link). I ended up noticing that the bottom corners of the radiator were leaking coolant, and ended up replacing the radiator with an OEM part bought across the BMW parts counter.

Quote:
Originally Posted by TurnersInOz View Post
You can also try swapping the sensor on the ET with the one on your washer fluid tank to see if the issue goes away.
I like this idea; however in the process of swapping the sensors - am I going to introduce air into the cooling system (or just lose coolant)?

Quote:
Originally Posted by TurnersInOz View Post
Also, you say that you saw coolant leaking from the bleeder screw. Was this actually leaking, or were you referring to when you tried to bleed the system?
I'm referring to the bleeder screw (part #2 link). The coolant only leaks when I purposely loosen the screw.

Yesterday evening the low coolant light came on twice during my commute (car was warmed up; about 20 miles - mostly highway driving) so I left the engine running, turned the heat to 90f, popped the hood and loosened the bleeder screw. I had a rag over the hose because I wasn't sure how pressurized the system would be if I over-loosened the screw. I was slow to loosen the screw; I didn't hear any obvious air hissing - and then I eventually got to a point where the rag quickly became wet with coolant so I closed the bleeder valve.

And I noticed the problem on my commute in this morning.

Last edited by Sigrid7993; 01-17-2014 at 04:16 PM. Reason: spelling.
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Old 01-17-2014, 04:15 PM   #5
Sigrid7993
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Quote:
Originally Posted by Sansho View Post
If it's been working OK for awhile, and the coolant level is OK, I'd be inclined to second the expansion tank sensor. They run around $15 from a discounting BMW sponsor (I checked TheBMWPartStore.com)
I'm all for the problem being a $15 dollar sensor; however it doesn't feel right that the low coolant light turns on in the winter months; and then ceases to be a problem in the summer (when the heater would normally be off).
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Old 01-17-2014, 04:26 PM   #6
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I wonder if a symptom of gasket failure's from any of these parts would cause air entering the system as the system cools off? I haven't been able to locate any leaking coolant, however it can be easy to miss.

Once the car has sufficiently cooled off I'll check the expansion tank's coolant level gauge again.
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Old 01-17-2014, 04:36 PM   #7
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Does anyone know what temperature range the coolant should operate at?

I know that the e46 dashboard coolant gauge is not designed to provide an accurate reading; and is instead designed to tell the driver if the car is warming up; operating at normal temperature (middle or 12'oclock position), or all of the way to the right (ie. serious overheating and/or loss of coolant).

There does happen to be a hack for the onboard computer (the button at the end of the stalk that cycles mpg/clock/average speed/average mpg). With this enabled, item 7.0 will digitally read out the current coolant temperature value in degrees centigrade. For those that are interested in knowing more ( link ).

Perhaps I can find a relation between the digital coolant temperature readout & when the low coolant light turns on & off.

Last edited by Sigrid7993; 01-17-2014 at 05:08 PM.
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Old 01-17-2014, 04:42 PM   #8
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I had the same problem... all of the sudden I started getting low coolant light from time to time. After a month, turned out my 10K mile thermostat was broken!
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Old 01-17-2014, 05:13 PM   #9
Sigrid7993
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Quote:
Originally Posted by MrSlacker View Post
I had the same problem... all of the sudden I started getting low coolant light from time to time. After a month, turned out my 10K mile thermostat was broken!
Did you learn of the thermostat failure via a check engine light?

From my understanding; these thermostats are designed to fail in the always open position. Which is easy to diagnose because the car's heating system doesn't work well, and the dashboard coolant gauge tends to not reach the middle (12'oclock position).

My heating system has been working well...
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Old 01-17-2014, 05:29 PM   #10
Sigrid7993
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I just took a photo of the coolant level dipstick (found in the expansion tank), if anything it may be slightly too high?


I also took a photo of the expansion tank's cap; the two seals look good to me (not rectangular/flat)


Edit: The white powder/dried coolant found ontop of the expansion tank in the first photo wasn't there last night (when I decided to open the bleeder valve after my commute).. So I'm confident that is left over coolant that didn't get absorbed by the rag.

Last edited by Sigrid7993; 01-17-2014 at 05:33 PM.
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Old 01-17-2014, 07:45 PM   #11
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Quote:
Originally Posted by Sigrid7993 View Post
Did you learn of the thermostat failure via a check engine light?

From my understanding; these thermostats are designed to fail in the always open position. Which is easy to diagnose because the car's heating system doesn't work well, and the dashboard coolant gauge tends to not reach the middle (12'oclock position).

My heating system has been working well...
I did not have check engine light on. However when my buddy hooked up his computer to the car, it did give him thermostat error. I also had some visible coolant on the outside of it after i removed it. I had perfect heat the entire time and car drove exactly in the center of temp gauge.

Keep in mind, thermostat was replaced about 1 year ago (10k) miles.
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Old 01-17-2014, 08:12 PM   #12
Sigrid7993
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Quote:
Originally Posted by MrSlacker View Post
I did not have check engine light on. However when my buddy hooked up his computer to the car, it did give him thermostat error. I also had some visible coolant on the outside of it after i removed it. I had perfect heat the entire time and car drove exactly in the center of temp gauge.

Keep in mind, thermostat was replaced about 1 year ago (10k) miles.
Thanks. I'm going to look into getting a tool that pulls the BMW codes in addition to the OBD2 ones.

Were you topping up coolant or anything like that?
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Old 01-18-2014, 02:26 PM   #13
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I have a similar problem. My light has only come on twice this winter but its definately got my attention. Ill be following this thread for results. GL OP!


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Old 01-18-2014, 03:10 PM   #14
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Quote:
Originally Posted by Sigrid7993 View Post
I just took a photo of the coolant level dipstick (found in the expansion tank), if anything it may be slightly too high?


I also took a photo of the expansion tank's cap; the two seals look good to me (not rectangular/flat)


Edit: The white powder/dried coolant found ontop of the expansion tank in the first photo wasn't there last night (when I decided to open the bleeder valve after my commute).. So I'm confident that is left over coolant that didn't get absorbed by the rag.
Your coolant level is too high. The top of the float should not be above the rim of the ET. You risk blowing out the ET due to excessive pressure. Take a poultry baster and suck some coolant out. Also check your temps using the OBC. See jofj's thread on how...


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Old 01-18-2014, 04:14 PM   #15
TurnersInOz
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Did you replace the cap? In the pictures it looks like this may be an area where coolant is escaping.
Swapping the sensor will not introduce air into the system as it is not in direct contact with coolant.
Once you've bled the system, I'd leave the bleeder screw alone. Use the float in the ET to determine level.
When the coolant level is correct, the top of the neck of the ET will be in between the two spheres on the float. Yours does look high, and if that is the case you should remove some.
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Old 01-18-2014, 05:23 PM   #16
Sigrid7993
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Quote:
Originally Posted by TurnersInOz View Post
Did you replace the cap? In the pictures it looks like this may be an area where coolant is escaping.
Swapping the sensor will not introduce air into the system as it is not in direct contact with coolant.
Once you've bled the system, I'd leave the bleeder screw alone. Use the float in the ET to determine level.
When the coolant level is correct, the top of the neck of the ET will be in between the two spheres on the float. Yours does look high, and if that is the case you should remove some.
Yes, summer of '12 I replaced the ET cap w/Expansion Tank. It looks like coolant has been leaking because two nights ago I tried bleeding the system using the philips head bleeder valve that's in close proximity. Prior to opening that valve the ET / Airbox area was clean.

It's good that I now know the water level is too high, I'll lower it prior to my next drive and report back.
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Old 01-20-2014, 12:32 PM   #17
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I apologize in advance if I"m further complicating things. However I believe I had not let my car cool enough prior to taking the photo of the expansion tank dipstick.

This current photo is after the car has been off for 16+ hours, sitting in a heated garage.
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Old 01-20-2014, 12:39 PM   #18
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That looks about right ... not quite to the max mark ... that's where mine sits.
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Old 01-20-2014, 01:23 PM   #19
Sigrid7993
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According to the diagram on the expansion tank; the red level should be between the 1st and 2nd sphere - so I sopose the coolant level is correct.

I'm going to try bleeding; loosen bleed screw so air can escape, set heater to 90f, lowest fan setting, rev engine a couple of times (leaving engine on for no more than 30 seconds), close bleeder screw. Go for another drive to see if symptoms have changed.

If that doesn't correct the intermittent low coolant light; I guess I will buy a replacement coolant level sensor and see where that takes me.

Last edited by Sigrid7993; 01-20-2014 at 01:25 PM.
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Old 01-21-2014, 09:41 AM   #20
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An intermittent low coolant light can be caused by a bad switch in the underside of the tank. You can replace it without losing any coolant. Takes about 5 minutes. Check the connector first- it may be loose. Also if you have a coolant leak the coolant could be shorting out the switch's pins.


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