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Discussion Starter #1
Wife’s e46 wagon has a low coolant light that comes on shortly after switching to heat, goes off as heat is turned off. Swapped level sensors, no joy. Coolant level is correct. No signs of leaks. Temp is rock solid.

Likely going to do water pump soon will I need to replace coolant tank? Any thing I can test to find the source of the odd symptom?


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I would try bleeding the system again, there are probably air bubbles in there and it should go away.
 

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In my experience, the heat opens the heater core and more coolant flows there giving the low coolant warning. Check the coolant in the morning when it's cold and also bleed as well. That should solve the problem.

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You don't have to change the tank when you do the pump If you bleed the system cold with the key in pos 2, the heat set to high and the fan on low the heater valve will be open and any air should bleed out. The heater valve should be open by default but it won't hurt to have the heater on. Putting the car on ramps always works for me.


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Discussion Starter #5
Thanks, I’m curious, the cold bleed in key position 2 implies that there is a coolant pump between the tank and the firewall? My X5 has one, don’t think this e46 does. Or, did I not get your point?


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There's no auxiliary pump on an e46, they just specify the key to be on with those settings. It's worked every time for me. Just slowly fill the tank with the bleed screw out till there's a solid stream of coolant coming out of it. The put the screw back in, remove the excess coolant from the tank, put the cap back on and start the car. Run it to temp and check for good heat, if it doesn't overheat during a test drive you should be good. Check the level daily when it's cold and adjust until it stabilizes.
 

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When bleeding, Switch climate control to heat so it will open heater valve and coolant will circulate trough heater core.
 

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When bleeding, Switch climate control to heat so it will open heater valve and coolant will circulate trough heater core.
I do that too, but there are a few people on here that claim the heater valve is open with the key off.
 

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I do that too, but there are a few people on here that claim the heater valve is open with the key off.


Yes it opens when you off engine. And obviously closes as soon as you start engine, and remains closed till you switch heat on. So you bleed system and have to make sure there is no air stays in a heater core so you put climate to heat and it opens the valve.
 
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