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

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Kyle De Priest
2007 e320 Bluetec
2013 GLK 250 Bluetec

If it is not overheating while driving the water pump and radiator are fine. Most likely the fan clutch is not working like it should. Even if it seems to spin fine it may be spinning to slow, getting enough air though the radiator takes a lot of force.

I agree that the fan clutch is probably bad.

You can test it by: when it is 'overheating' (up over 110 C) stop the car, pop the hood, and see if the fan (inward or the radiator) spins easily. If it has no resistance it is bad.

Also sounds like your auxiliary fan may be bad.

How hot does it get in traffic?

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

You can also do the broomstick trick. Be careful!

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

don't replace the fans yet. check the temp switches first if they're working.

Replacing expensive parts is never a good way to diagnose a problem.

Diagnosing a failing fan clutch is easy. Let the engine running until it is above normal operating temperature (not to hot). Stop the engine with someone watching the fan. If is does not stop immediately if the engine stops it is defective (or the bold that attaches the fan to the clutch is loose).

Never stick something in a running fan, that is very dangerous, the fan will break and parts will fly out.

You may also check if the fan cowl (the plastic thing around the fan) is properly seated, if air can enter between the radiator and the cowl cooling is dramatically reduced.
If you do not know the history of the car check also for the less obvious mistakes in the past, like mounting the fan the wrong way. If it tries to blow the air towards the front cooling will not be as effective.