2007 4.8i Low Coolant Warning but tank full

[Wahooz]

Hi all,
I finished doing a ton of work on my 2007 4.8i, including valve seals, water pump, valley pan, and coolant transfer pipe. Anyways, got everything back together, truck runs amazing and no more smoke from valve seals, however, I can't seem to get rid of the "Low Coolant" warning light (yellow).

I used a vacuum system to pressure test the system and it held -27Hg vacuum for several mins, telling me there are no leaks or cracks in my expansion tank (which is only two years old...replaced it once already). Upon filling system via vacuum, and properly topped up to min level in tank, still get "Low Coolant" warning light. I've replaced the coolant level sensor in then bottom of the tank w/ a genuine BMW sensor, I've replaced the tank cap w/ genuine BMW expansion tank cap, I've bled the system, but still get the low coolant warning.

I'm kinda thinking I have air bubbles in the system, as heat is not that hot and fan comes on immediately upon starting the truck. Since I have a 2007 w/ mechanical water pump, I tried bleeding first by simply putting the temp on max and fan on low. That didn't work, so I tried the method of running the truck w/ cap removed. Is there another way to bleed the system since there are no bleeder screws? Supposedly self-bleeding system....

Another thought was a stuck thermostat, as i reused the old t-stat from the busted water pump. Could that be contributing to the low level warning? Any other thoughts or ideas? Thanks in advance-

[mkurniawansyah]

Originally Posted by Wahooz

Hi all,
I finished doing a ton of work on my 2007 4.8i, including valve seals, water pump, valley pan, and coolant transfer pipe. Anyways, got everything back together, truck runs amazing and no more smoke from valve seals, however, I can't seem to get rid of the "Low Coolant" warning light (yellow).

I used a vacuum system to pressure test the system and it held -27Hg vacuum for several mins, telling me there are no leaks or cracks in my expansion tank (which is only two years old...replaced it once already). Upon filling system via vacuum, and properly topped up to min level in tank, still get "Low Coolant" warning light. I've replaced the coolant level sensor in then bottom of the tank w/ a genuine BMW sensor, I've replaced the tank cap w/ genuine BMW expansion tank cap, I've bled the system, but still get the low coolant warning.

I'm kinda thinking I have air bubbles in the system, as heat is not that hot and fan comes on immediately upon starting the truck. Since I have a 2007 w/ mechanical water pump, I tried bleeding first by simply putting the temp on max and fan on low. That didn't work, so I tried the method of running the truck w/ cap removed. Is there another way to bleed the system since there are no bleeder screws? Supposedly self-bleeding system....

Another thought was a stuck thermostat, as i reused the old t-stat from the busted water pump. Could that be contributing to the low level warning? Any other thoughts or ideas? Thanks in advance-

Does the water level actually gone that low when the light's up? Maybe a bad sensor/contact?

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[Wahooz]

Coolant level does not drop in the expansion tank...in fact it rises a little as it gets up to temp. Cold the level is at the min mark but as it approaches 220 degrees, the level rises to just below the neck. Of course this is with the cap off so I can bleed it and monitor level. Also, put a brand new level sensor in .

[Wahooz]

Anyone?

[80stech]

Unplug connector and try open and shorted to see if light goes out. That way you rule out everything but the sensor/expansion tank.

[Wahooz]

Originally Posted by 80stech

Unplug connector and try open and shorted to see if light goes out. That way you rule out everything but the sensor/expansion tank.

Unplugged the sensor but warning still showing. Does the 2007 tank have a floating magnet like previous generations? I know there’s no bobber in the tank but wondering if it still uses some kind of floating magnet since it still uses the sensor in the dry well. Perhaps my magnet is stuck? Thank in advance all

[the_ulf]

the only electrical connection into the expansion tank is for the sensor that sits underneath. since those expansion tanks all prematurely fail and they all come with the sensors included, maybe just stick your ears out and see if someone who replaced their tank recently might still have the old sensor sitting around.