The electric fans are only really important if you are running the AC, other then that they almost never come on. On my SDL at least they don't kick on until 105C.

I'd say the viscus fan clutch is week, or your radiator is clogged. Overheating under heavy load is a classic radiator problem.

Thanks.
 

Thanks Hatterasguy. Would you still think that the radiator is the problem even though it was changed by MB 34,000 km ago?

I read on the other thread that the Aux Fan should be running the same time the main clutch fan runs. I guess this person was wrong?

Thanks. I guess I'll take your advice and flush the radiator this week.

This task is not the most simple of tasks.

When you remove the radiator from the vehicle, hold it up to the sun. If you see accumulated debris in the fins, it's your task to remove same. Water from a garden hose won't cut it. Compressed air won't cut it.

The solution is the use of a commercially available condenser cleaner in conjunction with compressed air. Careful use of a pressure washer will also assist in the task, but, extreme care must be used to prevent bending any fins.

It's a very common problem with M/B radiators due to the very close passages between the fins. My SD is running warm now........nearly all the time.........even at 75° ambients..........without a/c. The culprit is surely the radiator as it has a new water pump.

The fans are never the culprit if the vehicle is at highway speeds.

Yes, anything could have happend in 34k Km's. Heck the car could have sat in a garage and their could be nuts and a mouse nest in between the condensor and radiator.

I thought I posted this yesterday - oh well ...

I think this is a pressure issue:

1. Water pump seal -check for seepage at the weep hole
2. Reservoir leak (above the coolant level) -usually in the area of the neck (the cap could be OK, but still not hold pressure due to another leak)?
3. Head gasket leak - worst case, but could account for the spikes in temperature you are experiencing

Fix cheapest first - 1 and 2, above, are easy and inexpensive. 3 is expensive, but with megamiles, possible.

Mechanic's Advice
 

I spoke with a MB mechanic this morning.

He said it's probably either my Auxillary Fan or the 100 degree Switch.

He suggested I try to turn on the Air Conditioning and then the Auxillary Electric Fan in front of the radiator should begin to spin. This was suggested in the thread earlier. Well the fan didn't spin. The temp guage was at about 60 degrees so it wasn't hot, but I understand that the fan should still spin.

So...I think I have either an Aux. Fan problem, or the 100 degree switch problem.

Can someone give me some insight into these two possible problems? How hard is it to change these two myself. Any insight into diagosiing and fixing would be appreciagted.

Brad.

Doc:

A 1,200 foot climb over 3 kilometers is significant. What is the ambient temperature when the temperature climbs?

Check the link below. Especially items #'s 17 & 18.

http://pages.prodigy.net/jforgione/MB_S500.html

Good luck.

Let us know what worked (if you were able to fix the problem).

drbrad,

Are you replacing anything as we go through these discussions? Likely, you won't find "the" single thing the first time out - I'll watch the discussion and look forward to seeing what you have actually done related to the many things you have heard.

Please let us know how it goes.

Yup
 

Yes, I've been doing almost everything everyone has suggested.

• replaced thermostat with new MB thermostat (opens at 84 degrees celcius)
• replaced rad cap with new MB cap from dealer.
• Flushed rad and changed coolant.
• Checked fans. Appear to be working, at least the one that is behind the rad.
• Trying to figure out if the Aux. fan is malfunctioning. Turned on A/C and the fan wasn't spinning.
• Bought a new 100 degree switch today at lunch and will replace that tonight.
  • Any new suggestions? Thanks to all....
    
    Brad.

Hey doc- an RN from Chicago consulting with you here! Our 190d had similar symptoms where sitting in traffic idling for long periods, and driving up steep inclines at highway speed would cause the temp to climb relatively high on the guage. After chasing several possible causes- I ran her till she got hot, and saw that the fan would not engage. I used a jumper wire to activate the magnetic fan clutch (which clicked beautifully), so the switch that activated the clutch turned out to be the first problem. I replaced it for $40 US. After the AC was repaired she began to overheat again- this time it was a disconnected wire to the pusher fan similar to the one you have described. With these two problems addressed she rarely runs hot- even at highway speed, with 4 passengers, climbing a hill with the ac on. I think you may have found your problem in the switch- with the new cap and flush you've done good preventative maintainence as well. Good luck- John

Problem Solved?
 

Hi guys:

I've solved the problem with assistance from chiro, a member on this forum and everyone else's suggestions. Chiro showed me how to ground out the switch to test if the Aux. Fan was okay and that the switch was malfunctioning.

We grounded the 100 degree switch as recommended by grounding it to the block. Guess what???? The Aux. Fan kicked in and the temperature began to drop.

I will install the new switch tomorrow and let you all know how I made out.

I have to thank everyone for their suggestions and I am looking forward to using my A/C again!

I will recap what symptoms I was having and what we did and how we resolved the problem, once the switch is installed and tested.

Thanks again,

Brad.

Aux fan switch
 

What is the part number for the Aux fan switch? I have the same problem and want to install the 100 degree switch, the car originally came with the 130 degree switch 0085424517, but I want the fan to come on sooner. Thanks

Part Number
 

Hi fbotros:

I bought the part from Mercedes Benz Canada for $55.65 (CAD)

The part number is A 006 545 14 24. ("SWITCH.AUXILIARY FAN")

I still haven't installed it as I have to wait for the engine to cool. It looks relatively easy to install.

I've had the Aux fan grounded and running and the car has remained at a constant 84 degrees all day. It's been pretty hot today 23 degrees celcius, and I've had the Air Conditioning on.

I'll summerize everything once I get the switch installed.

Thanks to everyone!

Brad.

Well, I guess that explains why my auxillary fans do not come on..... my A/C is on the fritz. :rolleyes:

Of course the temp will drop if the aux fans come on, they move a lot of air!

But you are barking up the wrong tree with that one, they don't do anything until 105C. If you are by passing the switch to make the fans run all of the time, you will burn them out. Also this is a band aid at best over the real problem.


Under normal driving the temp should stay between 80C-90C, and the aux fans should never come on. Unless you have the AC on of course, even then they seem to cycle.