Overheating solved! Just a little background info for anyone with issues running hot: I bought this car in a somewhat neglected condition 3 months ago and noticed that even though the temperature gauge read around the 1/4 mark, the car seemed to run hot. All of the gauges actually read low (I think the car has a 325i cluster in it), so I became pretty convinced that I had an overheating issue. The temperature would also climb slowly but surely when stopped, returning to the 1/4 mark when moving. Since the car seemed to run hotter when stopped, the first thing I did was test and replace the fan clutch. After that, the car still would run hot and the temperature would climb, just more slowly. At this point I think I have either a faulty water pump that isn't moving enough water at idle speed (is this even possible?) or clogged coolant passages that during heavy load on the cooling system overwhelm the ability of the system to dissipate heat. So I set about thoroughly flushing the system as detailed in this thread. I also removed the old thermostat, which looked quite crusty. The result is that the car runs 2 or so needle widths cooler and holds steady temperature at idle. (this is after an hour long highway jaunt in 90F weather, so it's not just not up to temp because of the missing thermostat - and yes I'm getting another). Moral of the story: slow temperature climb at idle isn't always an airflow issue. Check for clogged radiator/block passages or a faulty thermostat. Now to find the coolant leak...
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