Coolant bleed problem - 1997 540i
 

I was bleeding my coolant system after changing my water pump and hoses, had the expansion tank cap off and the bleeder screw out. Added coolant to expansion tank as coolant and bubbles bled out of bleeder hole, heater on max, engine at 2000 rpm. All was going well, lots of air escaping when suddenly coolant started coming out of the expansion filler hole and the bleeder hole. Don't know what the problem is...thermostat?

Any help would be greatly appreciated!

just maybe you overfilled it, coolant is definately supposed to come out of the bleeder screw hole, i wouldnt worry about it honestly, i would just bleed it again, and once a tiny bit of coolant coems out the bleeder hole, stop it, and then see if the car overheats

:doh That's how you know the system is full when air comes out then coolant. When coolant finally trickles out = air is gone.

The problem is that I continued to see air bubbles coming out of the bleeder hole up to the point where coolant flowed out of the expansion tank so the air was not completely purged. According to the DIY on steeringzone.com I should be able to replace the bleeder screw after the bubbles end and see the coolant flowing back into the expansion tank through the return line.

Acutually that was on understeer.com, sorry...

To see if your t-stat is working properly, feel and squeeze the top radiator hose. If there's pressure while the engine is running warm, then coolant is flowing through it and it's opening properly. You may have just gotten a large air pocket come out. Try it again. Your temp gauge should also give you a clue as to whether or not there's a problem.

Personally, I find it easier to leave the bleeder screw on, and watch the flow back into the expansion tank. When you see a steady solid stream at around 2500rpm with the heat full on, you're good to go. If it's coming out in spurts, then you're not done yet.

The method I prefer is to bleed it as you did, put a few miles on it, and re bleed it a couple of times after a couple of driving cycles. This way it takes into account the thermostat going through a couple of cycles and the heater circulating

Thank you for your help, I will rebleed the system again today.