Is it strange at all that the only time that this problem is coming up is after an uphill climb at a stop, or is that pretty typical for intermittent overheating problems? It doesn't overheat at all in normal around town driving or the downhill drive to work, or the drive up the hill until I stop, even in 90 to 100+ outside temps.

It could be a typical indication that all cooling air through the rad is lost when you stop at the light. Thats if the fluid filled clutch that holds the fan is shot. This would also allow the engine to store more heat up all the way up the hill than should be present.

With the engine at normal operating temperatues it should stop the fan turning fast when you have someone shut off the engine. Also when hot with the engine stopped see if you can turn it with the fan blades easily by hand. Remember the fan clutch is controlled by temperature.

If the fan fluid clutch checks out as good. You could source a new radiator youself and install it for a lot less than you have been quoted I suspect. You will have to get your hands dirty though.

I agree with the others, sounds like a fan clutch problem.

Thank you for all the feedback guys. Ok, so when I get a chance to get under the hood of my car this weekend, the symptoms of a fan clutch problem I should be looking for are:

1) If the fan keeps spinning after I have someone shut the engine off when it is hot.

2) If the fan blades DO turn easily by hand when the engine is off and hot.

While I learn quick and can follow instructions well, this is foreign territory for me. Are there guides on this site that I can dig up for doing this replacement?

I assume this is going to entail unbolting the fan and it's belts from the clutch, swapping it out, then re-attaching the fan and re tightening the belts? A mercedes OEM one of these is coming up as a couple hundred bucks, whats the best aftermarket less expensive option?

There is no need to remove the belts.

When the engine is up to temperature, you shouldn't be able to stop the fan from spinning. The easiest (safest) test is to try to stop it with a rolled up newspaper with the engine running. If the fan stops, you should replace the clutch.

Replacing the clutch requires removal of the fan/clutch assembly as a unit (you do not have to remove the belts or pulley). Removing the fan assembly requires loosening four bolts with a skinny wrench, take a look and you will see what has to be done.

The quick and easy test for a viscous problem is to (carefully) stick a fresh carrot into the fan blades (engine running up to temp of course)

If the carrot stops / stalls / significantly slows the fan, the viscous coupling is gone.

Nothing actually stopping you botching a viscous coupling to make it locked up permanently, it's only a fuel saving measure, a fan will draw up to around 1.5 BHP at revs.

Evening update:
I took it slow tonight and kept it between 50 and 55, and when i started getting close to the top of the hill I turned on the EC heater full blast. The temps never passed 100 while I sat at the stoplight. Interesting?

The heater was removing heat instead of the radiator. Check the fan clutch and let us know what you find.

As an almost totally irrelevant aside, my 307d with a 616 had a slot and a metal tab built into when. When the viscous coupling failed, you pressed the metal tab into the slot and it became a fixed bladed fan. Pretty nifty feature I thought.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13