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Discussion Starter #1
Hello, I drive an '87 300DT with about 180,000 miles and had a question regarding the aux fan. Does the aux fan operate without using the A/C when vehicle reaches a certain temperature? I recently installed a 'Cool Harness' and the aux fan isn't kicking in at about 95C. I also replaced the coolant temperature sensor, too. Could the aux fan relay be bad? If so, which chrome cube is the aux fan relay?
Please advice and thanks for your help and expertise!
 

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Does the aux fan come on at a certain temp. Yes.

Are your temps regularly exceeding 100C? If they are then you have something to be concerned with, maybe.
 

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Check the aux fan resistor behind the driver side headlight. It is a often overlooked item that causes a non op fan.

I am not a big fan of the cool harness. IMO, it just a band aid that covers up other cooling system problems such as worn/bad fan clutch, clogged radiator, etc.
 

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Discussion Starter #5
Thanks for the tips! I had the fan clutch replaced about one month ago and I'm going to install a Mbz water pump and thermostat (80C) this coming weekend. The temp tends to go up only in city traffic, will usually hover between 100C and 105C in stop and go Los Angeles traffic. As soon as I get moving, temp drops. Thanks, again.
 

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Sounds like a lack of airflow. Since you're already doing a water pump job, make sure to pressurewash the cooling fins on the A/C condenser (front and back) and the radiator (front and back) and the space in between.

And don't forget to remove the aux fan shroud and clean out the gunk that tends to accumulate there like a vacuum cleaner bag.

IF you still see temps above 100C after doing the above, then you might have gotten a bum fan clutch. Did you install a new genuine MB unit?
 

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Discussion Starter #7
Thanks again for the great tips, really appreciate it. I'm also replacing the tensioner belt shock because my mechanic noticed that the tensioner belt shock is loose/worn which could be causing cooling issues, too. I did not use a geniue Mbz clutch, used a Behr clutch (Not made in China, German made).
 

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There might be part of your problem. Behr clutches are not what they used to be. Do a forum search on one of my fan clutch tales. Went through 3 Behr clutches, all with the same symptoms as yours, until I finally coughed up for a new genuine MB Horton clutch.

Problem has never reoccurred.
 

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I love the cool Harness, not as a band aid, but as a backup. If everything is working properly it is not really doing much, but it is there to cover and get the fans on sooner if something else in the system goes wonky.

My Behr clutch lasted something like 10K, but I thought the Mercedes fan clutches were also made by Behr, no? The Sachs clutch I bought last time was made by Horton. Haven't had any problems with it so far...
 

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Discussion Starter #10
Hello, again. Have any of you bought a Niessens radiator for a w124 300D? I've read good things about them and they are still manufactured in Denmark.
Thanks!
 

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No on the Nissens. Why? 1) Because the radiator petcock is a unusual size and cannot be obtained separately. 2) No reinforcement at the connecting pipes, 3) Fit and fitment is not as good as the BEHR.

There is virtually no difference in price between BEHR and Nissens.
 

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Hello, again. Have any of you bought a Niessens radiator for a w124 300D? I've read good things about them and they are still manufactured in Denmark.
Thanks!
I put in a Nissens radiator a year and a half ago. I have not had any troubles with it, but would note a couple things:

1) There was a tab on the passenger side that I had to grind off with a Dremel so that it would fit properly with the radiator support.

2) It is true that sourcing a petcock, if necessary, could be problematic. It seems most likely that it is the same as some other Nissens radiator, but I have not been able to figure out which one or where to get it. Honestly, I may have gone with the Behr if I had known this before I got it.

3) There seems to be some disagreement about the lack of reinforcement in the connection necks. It seems that they are a bit heavier and more sturdy than the Behr, and perhaps a different material composition, so many feel that they are actually better than the Behr, which is seen as a flimsy neck with an afterthought "fix." Many others think the reinforcement insert makes the Behr better. This argument could probably go on for a long time...

FWIW, the radiator I replaced was the original and had small cracks in the upper neck when I bought the car. I drove it that way for another 5 years thinking the hose had just leaked a bit. I will need another 20 years or so to see how the Nissens holds up. ;)
 

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One of the W124s I had came with a Nissens installed. I was aware of the odd petcock issue, so I can give these words of wisdom.

1) Don't use the petcock, don't touch it, don't even look at it. Pretend it's not even there. Drain coolant by disconnecting the lower hose

2) Reinforce necks by inserting a copper sleeve and use epoxy to bond it to the end tank. Do this for both upper and lower necks, but particularly the upper neck.
 
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