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Hey there guys, I have a 2004 325xi.

When I bought the car it had a blown head gasket at about 247k. The car was running rough and was building exhaust gas pressure in the cooling system causing it to over heat/pop rad hoses and expansion tanks. Not to mention there was stop leak found.

I ended up swapping another motor with about the same mileage (247K) into the car, and since then it has ran like a dream.

Went about 5 months of DD with zero issues until one day the coolant light came on. Car wasn't over heating or anything just the light.

She was almost completely empty, so I then topped her off and then took it to work where I noticed that the expansion tank had cracked. Fixed that, bled the system and was on my way.
I noticed that my heater started to stop working, so I figured I hadn't bled the system out completely. When I popped the cap the expansion tank was dry.

A bit nervous I filled it and then pressure tested it. It held plenty of pressure so I bled it again. The heater still wasn't working.

So if I fill the system then crack the bleeder then hold the rpms at about 3K the heater gets warm then cools of when I take my foot off the gas.

If I hold the rpm's up for a while with the expansion tank cap open coolant will start to bubble and overflow like normal, then it will pulsate violently shooting coolant like a volcano.

Another thing I have noticed is that when I turn the car off then rad hoses both top and bottom will collapse.

There are no system leaks, system holds pressure.
Brand new Water Pump/Thermostat (Pulled and inspected, everything looks good.
No leaks inside the cabin (Suspected Heater Core.)

Coolant is constantly being lost, but there is no smoke and the engine still runs great. I tried too do a comp test but 3 of the cylinders had 120, and the other 3 read 0. That cant be right, the car still runs great so I'm still not sure what happened there...

When I replaced the engine the only components of the cooling system that weren't replaced were he radiator and the heater core. Do you think one of these two could be clogged or something all of the sudden?

The car hasn't over heated at all or anything else unusual.

No puddles or traces of lost coolant.

What do you guys think? Do I have head gasket on a high mileage engine or is there something else I am missing? A root cause failure?

Anything helps, I appreciate it...
-Gbro
 

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Here's an easy and free check.
- get the engine up to full operating temperature
- allow the engine to full cool (overnight is best)
- squeeze the upper hose:
* compresses easily: head gasket is likely ok
* hard to compress: head gasket is suspect

Also, you can buy test strips that will tell you when your coolant has combustion contaminants. Also, have a cooling system pressure check performed.
 
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