2003 BMW V6 330i E46 standard 5 speed tranny. Expansion tank blew up summer of 2009 while doing 85 on the interstate and it wasnt safe to pull over so had to drive another 3 miles with overheating engine. Towed it home and ordered parts; replaced the expansion tank, radiator cap, thermostat, water pump, top and bottom hoses, new coolant obviously, and removed the radiator for a good flush. Reassembled and ever since have had intermittent temp fluxuations, occasional rough idle, and rarely have some performance droppage (sputters slightly when accelerating rarely). I also have to release air buildup in cooling system after nearly every drive via the bleeder screw. I'm losing coolant everytime I drive through the radiator cap so i'm topping it off every day. I just changed the oil for the 3rd time since this occurred and am not seeing any foam or whiteish colored fluid in the oil. When releasing pressure through the bleeder screw it does seem to smell slightly sweet and exhaustish. Is it possible to have a blown head gasket without the coolant/oil mix? Based on what I have read on several bimmer forums i'm pretty sure it is the HG but i've also read that the temp sensor in the lower hose could cause the coolant loss as well. Planning on a new temp sensor just to eliminate the possiblility and was wondering if you had any other suggestions? Also was wondering if the head gasket "repair" mixes available online are worth trying or if they are mostly for suckers. Thanks for your time and advice!
Rather than "candy coating" my response, and due to the fact that I have 2 cars that are in the same place you are now, I need to be straight with you and tell you that the cylinder head will have to come off and be inspected for heat related cracks, and the cylinder block will need to have all the head bolt holes "timeserted" I am sorry about the bad news, but I dont make the news, I just report it.
The M-54 motor in your car is an Aluminum block, and when overheated the head bolts pull out. To save the engine and to have the car back on the road, you will need to have the aforementioned work performed. Let me know what you decide.