[UberXY]

A few weeks ago, our low coolant light starting coming on randomly, and now it’s on all the time.

1. The reservoir is at the correct level, and I bled the system with the heater on full max.

2. I use BMW coolant.

3. I replaced the level sensor yesterday. The light went out for a few minutes and came back on. When the car cooled I checked the coolant level and it was right.

Car is at 152k and runs well otherwise. It does not overheat and the temp guage never rises above mid mark.

Any thoughts?

[Wgosma]

Get the car's computers scanned and see if any related fault codes are present, go from there.

[Opie55]

Maybe wiring to the sensor or the connection plug itself is corroded or otherwise broken?

[UberXY]

I think it’s solved. I put on a new expansion tank, cap, and sensor. When I pulled the old tank off the bottom connections, the automatic transmission thermostat was in a bunch of pieces...springs, pistons, plastic bits, etc. so I replaced that too. Now no more low water light.

[Marty in NY]

Originally Posted by UberXY

I think it’s solved. I put on a new expansion tank, cap, and sensor. When I pulled the old tank off the bottom connections, the automatic transmission thermostat was in a bunch of pieces...springs, pistons, plastic bits, etc. so I replaced that too. Now no more low water light.

I have heard several owners complain about expansion tank failures, glad you got it fixed. Now you don't have to keep wondering if you have a real problem or not. Can you explain in more detail or post some pix regarding the ... automatic transmission thermostat was in a bunch of pieces???

[UberXY]

The thermostat is small cylinder about the size of a small flashlight maybe 3.5 inches long. It’s a plastic tube with some openings. Inside are two springs, and two small pistons on top and bottom. It fits in one of the openings where the tank plugs into at the bottom, and extens about 2 inches into the tank. I guess it regulates water flow into the small ATF heat exchanger.

Part 11 in photo. Prices for it were all over the map.

[Marty in NY]

Originally Posted by UberXY

The thermostat is small cylinder about the size of a small flashlight maybe 3.5 inches long. It’s a plastic tube with some openings. Inside are two springs, and two small pistons on top and bottom. It fits in one of the openings where the tank plugs into at the bottom, and extens about 2 inches into the tank. I guess it regulates water flow into the small ATF heat exchanger.

Part 11 in photo. Prices for it were all over the map.

Do you have the 4 cyl model? I went to Realoem to look for the diagram you posted, didn't see it, what section is it in?

Oh wait, just read what cars you have, you do not have an F25, correct? This issue was on either your '05 or '08 X3, correct? If so, you are in the wrong forum. This is the F25/26 forum

[pungo]

Originally Posted by Marty in NY

Oh wait, just read what cars you have, you do not have an F25, correct? This issue was on either your '05 or '08 X3, correct? If so, you are in the wrong forum. This is the F25/26 forum

Too funny, I was looking at the diagram and was like that's some older system, then saw you called them out...

[tqlla3k]

I just wanted to give people a heads up on how I fixed my issue.
Coolant light is off when car starts, after driving it turns on.

1) Replaced the switch, with the reservoir still in the car
2) That did not fix the problem
3) Played around with the coolant level float to see if it would come out
4) The tip broke by accident.
5) Put the cap back on

Problem went away. I installed this Aftermarket reservoir maybe 50K miles ago. I think the float deformed. so when the cap pushed the float down, the magnet at the bottom of the float was too far down. Breaking the tip allows the float to float higher.

I did this by accident, but
I would only do this as a last resort. Good luck.