Hi everyone:

So far so good.

Here's a summary of what has happened so far:

• the vehicle is a 1982 380 SEL 225,000 KM
• it has been fully serviced for 25 years at MB. (Even all of the oil changes.)
• the radiator was replace approximately 34,000 Km ago.
• about a month ago the car began to over heat and boil over when I drove up a steep long hill to my home. (Approximately 3 Km up to an elevation of 1200 feet.)
• the ambient temperature has been quite hot in the low 20's degrees celcius.
• the car was running between 80 and 100 degrees with normal city driving.
• I spoke to friends and posted this thread for some ideas.
• I first changed the thermostat. I used a MB thermostat that opens at 84 degrees celcius.
• I continued to have the problem. When I drove up the hill, the temperature guage would slowly rise and then spike to just over 100 then fall slightly then rise close to 120 degrees. Occasionally it would boil. (Four times in total.)
• whenever I started the car in the morning or drove down the hill, the temperature remained below 80 degrees.
• I replaced the radiator cap with a MB cap as suggested in this thread.
• no change with the new cap.
• I drained and flushed the coolant. Again, not much change in the symptoms.
• I checked the fan in the back of the radiator to see if the clutch had failed. I checked this by driving the car until it was good and hot, then I opened my driver's side window, opened the hood and reached in to turn off the engine while the hood was open. The fan immediately stopped spinning when the engine was turned off. I am told this indicates that the clutch had not failed.
• Next I was ready to tackle cleaning the radiator from the outside, when I noticed that there was an additional fan (The Auxillary Fan) in front of the radiator.
• I am told that this Aux. Fan helps cool the radiator under very hot conditions when there is insufficient air crossing the fins on the radiator.
• my next problem was to determine if the fan was broken or the Aux. Fan Switch.
• I grounded the Aux Fan switch and the fan spun. I am told by MB that these fans rarely fail. In fact they didn't have any Aux. Fans stocked in Western Canada and if I needed one, they would have to ship it in from Toronto. (Fan cost?.....$600.00)
• This indicated that the Aux. Fan Switch was malfunctioning. (The switch is located on the Thermostat Housing)
• I replaced the switch today and all is well. Switch cost: $55.65 CAD
• The car ran between 80 degrees and 100 degrees all day today. (I did a lot of driving, but the ambient temperature was quite cool at about 18 degrees celcius.)
• The temperature never rose above 100 degrees. When I drove up the hill, the temp rose to 100 degrees and by the time I got to my house, the fan had kicked in and the temp remained at 100 degrees.
  
  I'm pretty sure the problem has been solved. The ambient temperature is suppose to rise to mid 20s this weekend. I'll let everyone know how she fares.
  
  Wish me luck.
  
  I have to thank everyone for their assistance and suggestions. This type of forum is fantastic.
  
  Thanks again....
  
  Brad.

__________________
Dr. Brad

2003 C320 4Matic Station Wagon
2002 C240 Elegance
1982 380 SEL Star Certified