2001 BMW 530i coolant boiling

[Momma1963]

I recently had my water pump, water pump pulley and my fan clutch replaced. I took the car for a drive today and kept a close eye on the temperature gauge.
It was fine for the entire trip. When I got home and shut the car off, the temp gauge was still at normal. However, I could hear a bubbling sound coming from the overflow tank. I let the car cool down and opened
the rad cap. I then started the car for a few minutes and the coolant was boiling in the overflow tank! I shut the car off immediately. The top rad hose was hot, so from what I have been reading, it sounds like my thermostat is OK. What could the problem be? Was the system not bled enough when the repairs were done?

[Heel n Toe]

It was probably not bled properly.

Here is something you can do to check and rectify that. Make sure engine is completely cold... overnight cold... or at least, hood up, 4-5 hours cold.

Print this out and take it to the car with you... you will be glad.
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Cold engine bleed technique:
- open overflow tank cap and check/make sure coolant level is correct
- put cap back on, but not fully tightened
- turn ignition to last position before start position, but do not start engine
- set heater temp settings to max
- set heater fan manually to a lower speed
- start engine and within 30 seconds, gently rev it 3-4 times up to 2500-3000 RPM
- shut off engine before end of 30 seconds (before it starts to heat up)
- turn ignition back to the position just below start position
- open the overflow tank cap, and you should see coolant flowing into the tank because of the auxiliary pump
- turn off ignition, check coolant level, and top up if necessary
- replace cap tightly

This procedure is for pushing out any air pockets left by improper bleeding. In a day or so, if you still hear the bubbling sound, repeat the procedure.

If a repeat doesn't end the noise, take the car to your trusted indy BMW mechanic.