Hattie, the aux fan(s) can be tricked to go on at a lower temp than the factory set temp.

See below...

http://pages.prodigy.net/jforgione/MB_CTS.html

I used on of his switches in my fomer 1991 420SEL and it worked just fine in heavy, So. Calif stop and go traffic.

For some reason the W124, with the M103 engines tend to run a tad hotter than othe Benz engines.

So Far So Good
 

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.

86560SEL:

Try doing what I did. First ground out your Aux. Fan switch to see if the fan works. If it spins, the fan is probably good. Or you could try hooking the fan up to a 12 volt battery and see if it spins.

I've learned that if the fan is good, but it doesn't spin at high temperatures, your switch is probably at fault.

The fan will only spin when the temperature gets too high...and the temp would definitely rise with the AC on. I've been told that the fan doesn't necessarily turn on when the AC is on, just if it gets too hot.

Try changing grounding the switch and let us know if your fan works.

Hatterasguy, you're correct. The fan only turns on when the coolant temperature rises above a certain point. In my case 100 degrees. I ran the fan constantly by grounding out the switch as a short term fix until I could change the switch.

The switch appears to have solved my problem. I'm still not sure if the fan is suppose to run whenever the AC is on, or just when the coolant temp rises above 100 degrees.

Thanks drbrad for the part number, actually my car (89 300SE) uses a different switch, I got the part number from the dealer. I hope that solves my problem. Thanks again.

These cars shouldn't run near 100C during normal driving.

I've always read that 82 - 92 is the normal operating range for these cars.

The thermostat on the 617 is fully closed at 80°C. and fully open at 94°C. The gauge on the panel will probably climb a bit higher than this figure due to the location of the sensor.

By 100°C. on the gauge, the thermostat is certainly fully open and the cooling system is doing all it can possibly do with the airflow that it has through the radiator. Radiator airflow is assisted by two different fans and further assisted if the owner would clean the fins periodically.

Fin Cleaning
 

Thanks Brian, LGB and Hattie

What's the best way to maintain the rad? i.e. What's the easiest way to maintain fin cleanliness?

I think I'm running within normal range for temperature. The needle typically sits between the 80 degree and 100 degree marks, and only rises to the 100 degree mark when I go up the hill.

.........post #33.

Easy!
 

Thanks Brian:

I did read your previous post on how to clean the rad.

I was hoping there might be an easier way to do this. I'm not sure I want to tackle taking the rad out....

Brad.

Just for some perspective:

I took the rad out and spent two hours with compressed air and some foaming bath cleanser.

It was not all that clean when I finished, although it was significantly better than when I started.

Don't even bother to clean it in the vehicle.

Next time I use a commercial condenser cleaner or I'm not bothering either.

I did several 0-80mph WOT pulls today, 90 degree temps. I just managed to get the needle to almost move a bit, she was almost up to 85C!:D

Hill still the problem
 

Ok...I've been driving for a few days with the new sensor.

Under all driving conditions the car temp guage remains between 80 and 100....I assume it is running in the high 80s as it is closer to the 80 degree mark. I never hear the Aux. Fan kick in under normal city driving with the ambient temps in the mid 20s.

HOWEVER, the temperature continues to rise to just above 100 degrees celcius when I tackle the hill. No matter what the ambient temperature is, the Auxillary fan has to kick in to keep the temperature at just over 100 degrees. The car has NOT boiled, but it sure does rise when put under the stress of driving up the hill.

I am seriously considering pulling the rad out and doing the cleaning as Hatterasguy and Brian have suggested.

Any other ideas?


Brad.

Just as a reminder, it's a slow and tedius job. You can't clean the rad in 30 minutes due to the multitude of fine passages.

I have not mastered the art of the cleaning yet and will make an attempt with condenser cleaner, and, possibly some pipe cleaners.

Hold the radiator up to the sun and look between the passages..........you'll see what your task will be. When you get done, it should be perfectly clean through the passages..........not an easy task by any means.

If you have any tips after you do the job, please advise.

BTW, a temperature of 100°C. is nothing to be concerned about. Two of these will also bump 100°C. on any significant load.