Z3 replaced waterpump now overheating

Can someone pls help me. The waterpump went out. Replaced it along with the fan. Now car is running hot. Coolant is coming out top of radiator (coolant is cold), top hose is extremely hot, bottom hose is cold. Do you think its air in the system, stuck thermostat or something else? Also, heater blows cold, no smoke out of tail pipes. Any help would be appreciated. Thanks

Be very careful not to drive your car when it is over heating ! I'm not sure about the Z3 but, I know I had to bleed air out of my cooling system when I replaced my water pump in my Z4. If I were you I would go ahead and replace the thermostat. My Z4 has a screw by the rad inlet to let the air out of the system. I had to remove a cover plate that covers the top of the rad to get access to it. After I refilled my rad I put the cap back on and has the car warmed up I would loosen the air bleed screw and the air would come out . I did this until water started to come out thr air bleed screw. While doing this keep a close eye on your temp gauge. Good luck.

Thanks for the advice. I just hope it is not a HG or a busted head. I've read others say if your top hose is really hot and the bottom hose cold, while the car is trying to overheat, then its not the thermostat. I hope its just a air pocket. Thanks again.

You bled with heat setting on high? You kept the engine above 2k rpms to open the heater valve?

I did put the heater at full heat and on high, blew cold. I didn't keep the car above 2k rpm, I will try this tomorrow. Thanks for the info.

The heater valve needs the higher rpms before it opens. Any air trapped in the heater core will remain if you don't get the valve opened. Keep it at 2200-2500 rpms for a minute or so. If you have the heater fan set on high, you should be able to tell immediately when the valve opens and the coolant circulates (it will blow hot air).

Here's a video on how to bleed air from coolant.

Thank you for the video.

Thanks for the help guys. I changed the thermostat and its working great. I had no problems getting the air out of the system. I guess when water pump goes out it causes the thermostat to automatically close.

Very well done video! Thanks

Glad to hear it all worked out.

Glad to hear you got it fixed !

Originally Posted by jrblanks

Thanks for the help guys. I changed the thermostat and its working great. I had no problems getting the air out of the system. I guess when water pump goes out it causes the thermostat to automatically close.

More like a coincidence.

Glad you got it fixed.