300e Overheating but not losing coolant...

[DEPRIEST]

Hi All,
I've been doing a little reading of some previous posts, but I can't seem to find anything to address my specific issue...

My '86 300e is over heating in traffic. If let sit, it will get damn hot. If I'm moving, it's fine. If I turn the heater on, that will cool it quite a bit, but that's no kind of solution. It is not losing coolant. There is plenty of coolant and plenty of oil in the car and neither is mixing with the other.

So, after doing a little head scratching, I decided it must be the radiator. So just now, I changed the radiator and the hoses. My logic for this was... If the water pump was failing, it wouldn't send water through the heater core which in essence, helps to cool the car. Water pump (to me) seems to be in order. Also, if it were the thermostat, same problem... No water could get through, therefor, the heater core trick couldn't help with cooling the car. That leaves the radiator.

So I just changed it. (the radiator that is) Now, I added a bunch of Mercedes Fluid and water... and the car is still over heating when idle. Keep in mind, it's not losing water, so that must not be the issue.

So, I'm lead to believe one thing... Either I need to bleed the water with that 14mm bolt on the block. (how do I best do that again?) OR the little water pump's internal fan/propeller thingys are worn down and simply not moving enough water fast enough. The fan is spinning fine.

So, this is where I need your help. The termostat is easy, I *COULD* change that. The water pump looks hard. Is it? (btw, the radiator was a piece of cake thanks to the DIY section of this site) Based on the symptoms, is there anything else I should do before I tackle this water pump?

I appreciate your mental energy in helping me solve my issues.
-Kyle