'00 X5 4.4i cooling system
 

Hey Gang, Just had some engine work done (timing chain and guides) since the reassembly my temp gage is normal but I have coolant coming out of my over flow cap. Pressure test is fine. No codes. Thought it could be an air bubble in the top of the rad due to improper fill. Have been told by a BMW Buff that it could be a sensor. Apparently there is 2 sensors for the rad 1 that is read by the computer the other not but can affect the cooling system in this manner. Has anyone heard of this? or maybe some insight? Thanks.

I'm surprised to hear you have coolant coming out from your cap. What pressure cap do you have installed (marked on it in bars pressure)?
To remedy your problem I suggest loosening the bleed screw in the top of the expansion tank (looks like a plastic screw with a cross on top) to allow any excess air to escape from the system. From what I've read, it's easy to overfill the system, which can cause expansion tanks to split, so take care there's not too much coolant in there.

Thanks, I will check it out. I have changed the overflow(reservoir) cap twice. Display says low coolant after a few km drive and is leaking as I said from there. I top up to required amount but again leaks out. Overflow tank seems to be in good shape.

Sounds to me like you have air trapped in the system. When it was replenished, did they have the heater turned on fully? I'm very surprised to hear that you are still getting coolant coming from the cap - considering the OEM cap is supposed to have 2.0 bar pressure... I suggest ensuring the heater is turned on fully, get engine to operating temp and bleed the air out via the screw on the tank. My system has never leaked and the float indicator is quite low in the tank (I can push it with my finger and it moves a little but is no where near the top of the tank).