e36 cooling system mystery

Hey all, I'm trying to wrap my brain around a problem with my 1999 e36 328is and it's cooling system.    I replaced the expansion tank on the weekend, topped up fluid and "burped" the system.    Now when the engine is warm/hot, the fluid in the expansion tank drops until it's quite near the bottom.    If i let the engine cool, the level in the tank comes up a bit but looks super low.    Once I open the cap to refill, I can hear the vacuum "release" and the coolant gurgles and refills the tank to the top.   Do I still have an air bubble in the system?  I've tried another radiator cap and it's still the same and the thin overflow hose at the top doesn't seemed to be pinched.    Google isn't helping much. 

Thanks!

You are trying to fill a German cooling system.  If you can hang the car upside down, it might bleed...

Yes, you still have air.  There might be some sort of bleeder screw somewhere, or a heater hose or sensor you can remove to let the air out.

Did you perform the proper bleeding procedure? Get the nose of the car as high as possible, heat on full, and slowly fill the system. I can't recall if the E36 has one or two bleed screws, but you should have them open while filling, only closing once a steady stream of coolant flows.

Forget about Google and buy a Bentley manual.

I've had really good luck bleeding cooling systems with this:

https://www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY

It was the only way I could get my E30 to bleed properly. 

Try elevating the front of the car when you bleed it. Either on ramps or jack stands. 

I usually set the heater to full hot with the fan on high. Crack the bleed screw and remove the cap. Then, run it at idle while it gets up to temp. Then, rev it to about 2500 rpm for a while. Add coolant as you go. Once the heater blows hot both at idle and 2500 rpm, and you have a steady stream of coolant coming from the bleed screw, you should be good to go. 

The cooling system on these cars is such a pain. This procedure usually takes care of it though. Hopefully it helps!

This is also a symptom of a blown head gasket.  You can try rebleeding, this is what worked for me on my 98 M3...

Lift the nose of the car in the air.  Make sure you have a small hole drilled in the thermostat.  Start car, heater on full blast.  Fill tank, start squeezing the hoses.  Watch bubbles.  Keep adding coolant, keeping it at high in the tank as possible.  Once you stop seeing bubbles and are getting hot air out of the vents, turn the car off.  Allow to cool.  Cap on, start car.  Let it run up to temp.  Turn car off, let it cool and fill tank to the cold line.

Check this out -- bought it because it because of the 996, however now changing the coolant on everything is almost trivial.  

Drain the system (mostly.)

Connect to air compressor and flip the valve (venturi draws down a vacuum)

Close valve and validate it holds vacuum for 10min

Put the pickup tube into a 5gal bucket of fresh coolant and flip the valve....system refills and is self-bled.

Air Lift

In reply to fastbmw :

This is why an e30 expansion tank (self bleeding) is the ultimate upgrade. Have one on my ls swap and it it AMAZING after all of these years jacking with the OE expansion tank!

Thank you all,  I figured it was another bubble.   Back to the garage I go!

In reply to fastbmw :

You need to do a "drunk senior frat boy" burp on that. It's a pain, but somewhere is a big pocket of air.

In reply to Tyler H :

That is really cool. Thanks for sharing that! (adds to Amazon wish list)

I was having similar issues. My (finally) successful bleed had the heat on full, warmed the engine up with the cap off then taped my shopvac to the expansion tank and let it eat. Heat works now and my coolant level stays even.