X5 E53 4.8is oil in coolant

[peter71]

Hi, does anyone have any idea what causing the problem:
Recently fitted a second hand engine by my mechanic, engine bought from a trusted seller, and after when 1st started with a new engine just after 1 minutes some oil appeared in the coolant expansion tank. not a big amount just the top of the water
Engine running well, it was driven for 15-20 minutes for testing, water temperature ok, coolant pipes not hard, no water in the oil, no smoke or sweet smell from exhaust but my mechanic recommended a head gasket replacement, but Im wants to make sure whats wrong with it, might be a cracked head or block, so I dont wants to do any unnecessary work
there is any more place where the coolant able to mixing with engine oil?
any hose or oil cooler, any joint?
Thank you in advance

[wpoll]

What failed in the old engine - and could that failure have left traces of oil in the original cooling system components?

Might want to run for a bit more and see if it is really a problem or just residual oil from the work on the engine.

[peter71]

The old engine had a very low compression on 1 cylinder, other 7 was ok, just had a misfire
Checked with a camera and had some internal damage, scratch on the wall

[g300d]

Could also be transmission heat exchanger. Experienced this myself.

[peter71]

will check it up, how can I test it? have you got any idea?
Thank you very much