expansion tank hose to w.pump broke, while driving
 

I was driving on the highway today when a low coolant notification popped up. I continued to drive for around 15 miles, monitoring the temp gauge - when I came to a stop after exiting coolant started pouring out.

I identified the culprit as a broken hose from the new OEM expansion tank which feeds to the water pump (17127509966). The hose broke off at the water pump connector. Temp gauge stayed constant, in the middle the entire time.

Two questions:

1. Could this be a sign of a bad water pump - i.e. too much pressure in the line?
2. I noticed this small tube which looked kinda like vacuum line or something that was totally disconnected from anything - anyone know what it is?

BMW Hose part 17127509966


Thanks in advance

The vacuum line looks like the front differential vent pipe to me. It is not a problem, it's just venting pressure in the front diff when it warms up and cools off. It's supposed to be open to the atmosphere but high enough that if you drove through a big puddle, it wouldn't get any water in it.



If the coolant hose broke, it is probably time to do a full coolant system overhaul. Not sure of your mileage or maintenance, but if one hose is breaking that probably means more are going to break soon.

That is the vent pipe for the front diff NOT the cooling system.

thanks for the info - 197k miles, car had an engine rebuild prior to my purchase due to blown head gasket. I’ve had it for 30k miles and will likely redo the cooling system in a few weeks

I thought that same line was my mystery vacuum leak (never found), but it fooled me before I was informed of its' true purpose. https://xoutpost.com/1218990-post32.html

I've had mine for almost two years, and 1000 miles (only), so I haven't fully explored the nether side of the engine bay, yet.