 Cooling System Help Please!
Here is the story: I noticed that while driving on the highway my temperature gauge reads 1/4 [the top edge of the blue mark]. However, lately I have noticed that in idle the car starts warming up to mid mark and then to 3/4 mark. If I apply the accelerator it decreases down or if I go driving it decreases as well. Furthermore, when I was at a red light the heat would blow cold. Now, after searching this site and reading the Bentley Repair Manual; I came to realize that it could be a slew of different things. So, I warmed up the car to the mid point temperature mark. shut the engine off and felt the coolant hoses leading from the thermostat housing. The one on the right was warm [facing the engine from front of car view point] and then one on the left was lukewarm. I massaged the left hose moving towards the thermostat housing and I got a mild "burb" sound. Like something, perhaps an big air bubble, just passed through the hose. Then, I start the car. Holy ****, the car made a mild whining noise and had fairly bad vibration. It was abnormal. After about 1 minute of this, all of a sudden I hear a loud depressurizing noise. I cannot identify exactly where it came from however, on my engine, front side [above all of the belts and located on the left front edge of the valve cover] is a small device that looks like a miniature pump or regulator of some sort. I can take a picture and email it to whomever can help me identify it. In any case, I believe the sound came from there. After this, the engine purred just fine and everything was copacetic. The temperature gauge registered the mid mark and did not budge from there at all as I left the car idling for the next 10 minutes. When I drove around the temp gauge did not decrease but remained in the middle position. After about an hour and a half of sitting still [off] I start the car again and everything operates just fine. Gauge, after a while, registers the mid mark and the heat works 50% better. Even at idle the heat worked just fine. However, a couple of problems now came up: The car has a slightly more pronounced vibration now. Kind of like a set of bad spark plugs. [I just replaced them a month ago with NGK's]. Furthermore, if I push the "M" button the roughness of the idle decreases by 50%. Second problem, when I am sitting still and I turn the rear defroster on I noticed the rpm go down by about 50 rpm. perhaps a little more. In any case my normal idle rpm is about 750 and this looks more like 700 or 650. It happens for an instant and then it is gone. Long story short; What do you guys make out of this? I called the shop and found out that the previous owner, while maintaining perfect maintenance, apparently disregarded to flush the coolant system. Perhaps he did it at some different shop but the BMW dealership has no record and the private BMW shop that he went to afterwords for everything from oil changes, brake flush, and Inspection II [done last February] has no record of a coolant flush. So. My thinking is that I will flush the coolant. however, that doesn't explain the vibration issue and the decrease in RPM issue. What's the deal here? | 
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