E36 Check Coolant Level Warning Display

If you have ever flushed, drained, or otherwise changed the coolant in your E36 BMW 3 series, chances are you are sporadically encountering a 'Check Coolant Level' message displayed on your onboard computer display. No, this probably doesn't mean you forgot to tighten the block drain plug or the radiator drain screw. In fact, looking at bmw message boads like bimmerforums and roadfly, it seems others are getting this as well. The coolant level sensor goes bad. If you were low on coolant, clear your codes and see what happens. If it is the sensor, the annoying and misleading message can be eliminating by unplugging the two sensor wires, and jumping them. If this works, replace the sensor. If this does not work, the possibiltiy remains that un-bled air remains in the cooling system. Try using the bleed valve on the top of the radiator expansion tank (the screw with the long F-name...) and it THAT does not work, check this out:

Finally fixed my "Check Coolant Level" warning while shutting off the engine. Like most others, I tried all the usual fixes that were posted on various groups with no success. Recently while replacing the thermostat I noted that inside the expansion tank there is what I would call a siphon tube that the small bypass hose from the radiator attaches to on the expansion tank. It broke off internally and was loose inside the tank. I ordered a new tank from the dealer and installed it. After the usual bleeding of the system, the check coolant level warning during engine shutdown had finally been fixed. My theory being that the cooling system could not be bled properly because of the broken tube.

The air in the system was trapped because air would be drawn back into sytem through the broken tube. Nornally the tube would extend below the coolant level in the tank and during bleeding the trapped air would be purged and not drawn back into the cooling system. With the tube broken or cracked air is drawn back into the system displacing coolant. While the car is not running the coolant level appears good but during driving the coolant drops as the air in the system circulates with the coolant. This trips the OBC and the warning comes on after shutdown. So check your expansion tank for this possible problem.