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Discussion Starter #1
Hey all,

Its starting to get cold here in Memphis, we got our first frost a couple of days ago. After the first frost, on my drive down to Starbucks the low coolant warning light came on. This was the first time I had actually powered up the heater to full since owning the car. As I don't have an ice scraper I left the car running with the defroster on full and the heat at 80 degrees for about 10 minutes before my Starbucks run. Anyways about halfway to Starbucks the light came on, however, just as I was pulling into Starbucks it went out. On my drives around town Saturday I monitored engine temps carefully and they never exceeded the midpoint on the temp gauge. And yet the low coolant warning flickered on and off all day long.

I checked the coolant levels several times, once when the engine was fairly-warm and once when the engine was cold and the results were the same, coolant levels were normal.

I decided to run some tests and I took the car out this morning with the engine completely cold (it had been sitting overnight) but did NOT turn on the heat. The result: No low coolant warning light. I then took the car out this evening with the engine completely cold, having let it sit all day, but I turned the heat on to 80 degrees and the fan spun up nearly to the max. I did the exact same route as I had that morning and the result: about halfway through the low coolant warning light came on.

So from this informal test, it seems like this is some issue with the heating system...any ideas on how I can fix it? I'd rather not be freaked out by this low coolant warning light coming on all the time or worse yet become desensitized to it and ignore when I really do have low coolant! :eeps:

Any help is appreciated! :thumbup:
 

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This just happened to me. It ended up that everything was fine but the metal clips by the radiator cap were loose (probably from my mechanic removing the radiator cap after installing my new water pump). I found myself on the side of the road with a crap load of steam and coolant shooting out of there, so I just took out the metal clip, put the pipes back together, put the clip back in, put in some distilled water and bled the system a bit and filled it up properly when I got home. The low coolant light was on for days, I'd fill it up and it'd come right back on, then I finally figured it out. This might help?

Other than that, the car's big tank (coolant reservoir?) of coolant is known to go bad on the e46's, it's a $150 part.
 

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Discussion Starter #3
I don't think its the metal clips but I'll check tomorrow when I see my car.

I don't know if its a leak in the expansion tank or the coolant system. I don't think so, I did a fairly thorough visual check of what I could see and their were no significant drips under the car from what I could see.

Could this be a faulty sensor in the coolant tank somehow? Is the sensor fairly easy to replace?
 

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Its most likely your sensor, I had to replace mine twice on my own personal E46.

We have replacements available below...

Click HERE for more information.


Please let us know if you have any questions! Feel free to shoot me a PM or email.

Best,
Joe
 

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I don't know if this would hold true for the e46, but my e30 had been doing this exact thing. I replaced the sensor, and it went away...for two days. I was starting to get frustrated, because it was annoying. Level of coolant seemed fine. Right before I was going to unplug and short the thing to make the light go out, I instead decided to add a little more coolant even though it looked like it was at the proper line. Low and behold, the light went out and stayed out! Here it turned out that the level sensor only needed about 5 more ounces of coolant to be happy. I suppose it's just a little overly sensitive, like the gal I share a toothbrush holder with. LOL Try it, good luck. My e46 hasn't had this problem yet.
 

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I am firmly convinced that these cars have computer/sensor problems. I get all kinds of lights that come and go, everything from coolant to brake to DSC to SES. I can probably count on both hands the number of days I've owned the car that a light hasn't come on.
 

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When you turn on the heater, a coolant line opens and runs to the heater core. There is enough coolant in the system to keep the car from overheating, but when the heater core opens the level drops tripping the light. You need to add coolant with the heater on the bleed the system once the cars off and the air bubbles rise to the top.
 

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don't worry, as it gets colder the car starts pumping coolant into heater core which was previously closed. This may cause some drop in coolant level. Just top it off.
 
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