Coolant hose collapses when cool
 

Recently had a leaking coolant expansion tank that I replaced and refilled. Since then I've noticed that my the engine cools down, the large hose that runs from the waterpump to the top right of the radiator collapses.

Maybe hard to tell from the pic but the left side of the larger horizontal hose right before it splits and then connects to the waterpump is almost completely sucked in and flat.

Part #1 (the larger section) here: https://www.realoem.com/bmw/enUS/sho...diagId=17_0295.

No overheating issues to date. Just curious if this is normal or something I show be concerned about?

Yes, that is more or less normal as far as I know. Softer after-market hoses are worse. Having additional air in the cooling system (not full or not bled) makes it worse. If cap would vent at a lower vacuum it would help. It is a bit of a concern because I would think the constant flexing of the hose would weaken it. Maybe someone with new or old OE hoses could chime in.

I can see some residue around my coolant tank. So at some point I guess some has vented out the lid. I've also turned the bleeder screw on top of the tank a few times and let some air out. But not 100% sure what I'm doing when it comes to all of this...

to properly bleed turn the ignition on, but don't start the engine. Turn the heat on and turn it up to full high. this will kick on the secondary water pump. Remove the cap from the expansion tank and open the bleeder screw. If there is air in the system you will hear it as it bubbles out at the bleeder. When the coolant coming out the bleeder stops bubbling any air out you can close the bleeder screw, turn everything off and top up the tank.

I have tried this before and nothing seemed to happen after several minutes. Will try again.

So coolant will come out the bleeder (bubbling at first if air but then not)...but coolant will not come out the open lid?

How long should it run before you open lid and bleeder and see all this action?

you should see coolant bubbling from the bleeder if there is air in the system. You should not get coolant coming out of the expansion tank other than a little spray possibly as the secondary pumps coolant back into the top of the tank near the top. It can splash out sometimes. You can pop the cap and open the bleeder right after you turn the car on and crank the heat full hot (90 degrees). Putting on the heat full opens the valves to the heater cores and allows any air in there to escape also.

Got it! Just trying to figure out what to expect and see how messy it was going to be. :D Sounds easy - going to try this again...

Not normal. Your radiator cap has a vacuum valve in it which is designed to allow the system to return to atmospheric pressure after cooldown from a running engine. Try another cap.

Not normal! Sounds like your expansion tank cap isn't allowing the system to vent the vacuum pressure generated during thermal contraction as the car cools off. Try another cap and I bet the problem will go away.

I'll toss the old cap on and watch it for a few days and see what happens.


Attempted to bleed the system again today. Removed cap and loosened bleeder screw. Ran with heat all the way on high. It burped once or twice every 10-20 seconds. Let it run for 6 minutes.

Here's a video (after about 4 min of running) - note the burps around 10 and 30 seconds in.

Is that what it should be doing? Should I let it run longer (it never stopped doing this bubble every 10+ seconds)?