Cool Harness - Anybody here use one?
 

Has anybody here had experience with user -JimF's- "Cool Harness" product. I am looking to put one on my '95 E320. Please advise.

I just received mine in the mail today, but I had plans tonight so I won't be able to install it until tomorrow. It's supposed to be 90 degrees here tomorrow, so that should provide a great day to test it out. I'll let you know how it works.

I have an older version... made by someone else. Yes, they work.

There is no compatible connector. . .
 

for the E320's of '95 vintage and on. That year MB combined both sensors into a 'square' four (4) pin housing, so my CH doesn't fit this configuration. Also, bad news, there's no mating female/male connector to interface.

But contact Art Dalton. I believe he's familiar with that configuration to see if you can 'bridge' the appropriate pins.

JimF,

Isnt 95 the end of the w124? That's what he has. I thought things changed in 96.

Willy

Ok JimF, I guess I'll have to check around. Not a big deal, it just gets pretty hot here in the summer months, and I thought it might help. Thanks anyways

The new 4 prong sensors were from manufacture date of 9/94 on..prior was the single sensor...
The aux a/c fan resistor of the new sensor will be pins 2 & 3
[ br/yl - bu/gy ].
I have found the resistance of 15-1600 to be best on the 104s... They are avail at Radio Shack [ 5 for 99 cents].
Use metal film only ..

Pu in the Cool Harness Today
 

I found some time this afternoon to install the Cool Harness. Went for a nice long test drive, about 15 miles out into the country and 15 back into the city on the highway. Temp stayed below 100 most of the way, but did get up to about 102 during the stop and go traffic back in. I checked when I got back and both aux fans were running. I can say that overall it ran cooler for a longer period of time, and it peaked less than before. I think I may have some other cooling issues, but overall the Cool Harness seemed to help. BTW, it was a piece of cake to install.

Rich, glad it got there ok!
 

Check your af/water ratio: see Menu #17 for some tips. Currently using 35/65% ratio with MB AF and distilled water.

If you haven't flushed/changed your af, this might be a good time to check it out.

Good idea Jim. I did just have a flush and fill at an inde shop here in town. They were SUPPOSED to use MB AF, but when I checked it this weekend it was green. I believe if it is genuine it would be an orange color. I'll be draining and refilling with the proper ratio of "the real stuff" this weekend. I also wonder if the temp sensor might just be bad. I've noticed that I get up 80 degrees after only about 2 minutes of driving (Before I can even get out of my neighborhood). Thats first thing in the AM after sitting all night. Seems pretty quick to me.

In the past, I might have agreed . . .
 

with you re quick warmup. Before I changed my tstat, it would take a relatively long time to warm up which appeared ok!

But after changing it, you could see that the old tstat would not fully close, open about a 1/8". Thus the engine would take a longer time to warm up: that's maybe ok for SoCal but probably not good for any other place.

The replacement tstat does the same as yours: very quick warmup so don't think there's anything wrong.

But would advise the use of MB af and distilled water if you haven't in the past. Consider a good flush before refilling. And try the 40/60% mix (af/water).

...and oddly enough, when I had the flush and fill a couple of weks ago I also had the t-stat replaced! Sounds like you nailed that one!

I'm going to check the mixture ratio Saturday and see where it stands. I'm also going to call the inde shop and ask about the distilled water. It would not surprise me if they used it. The head Benz guy there seems to be really good. If not, I'll just do it over (myself this time) to make sure it's right.

While we are on the topic, would a shot of Water Wetter help?

BTW, what a great forum! Where else can you get this kind of info? This is like the Master Card commercial:

1993 500 SEL - $17,000
Annual maint........a XXXX-load!
Great information on how to do it yourself...PRICELESS!

Thanks Jim!

Didn't mention anything about . . .
 

Water Wetter but if you have read my page (menu #17), you know I use and recommend it.

Use 1oz per quart (S500 = 16qts) so that means, 16oz, about 1-1/4 bottles. Probably one bottle will be sufficient for your.

And don't forget the distilled water! Sorry to harp on this but, it is probably the most important item. Tap water is what destroys the effectiveness of af. Also plugs your radiator.

Sounds like a plan Jim. Thanks again for all of the great tips!

I'll let you know how it turns out.

new issues
 

JimF,

I did flush and refill with 60% distilled water, 40% MB coolant, and used the watter wetter. I'm still running over 100 when it's hot outside. I've also discovered that I have no heat in the car as well. I followed the tips on your site, and I get these codes from the A/C system:

Codes Meanings
E0 43 A/C system coolant temperature sensor (B10/8), open or short circuit **)
E0 74 Heater supply unit circulation pup (A31m1), open or short circuit *)
E0 75 Heater supply unit circulation pup (A31m1), open or short circuit **)
E0 83 Heater supply unit left duovalve (A31y1), open or short circuit **)
E0 87 Heater supply unit right duovalve (A31y2), open or short circuit **)
E0 99 Auxiliary fan, 1st activation, open or short circuit **)
E1 3 Auxiliary fan, 2nd stage activation, open or short circuit **)

Sounds like the heat thing is from a bad heater supply unit. But what do you think about 43,99, and E1 3? Could I have installed the cool harness backwards?

There's no polarity . . .
 

to a CH; you can't install them incorrectly.

But you could have a bad wiring harness; they do go bad. Just remove the CH and reset the codes. Wait a short time and re-read them.

Also use an ohmeter to tell if the B10/8 sensor is REALLY open; it should read around 350 ohms or so at 90C apx. If it reads open, or much higher than that, then r&r.

I almost went out to the garage and removed the CH to test, but It's past midnight here and if my wife finds me out there she will confim that I am actually, indeed, crazy! I'll try that tomorrow.

BTW, I just had the wiring harness replaced about 6 weeks ago.

Glad to hear that you can't install it wrong. I would have begun to doubt what limited mechanical ability I do have if I had messed that one up!

I'll let you know about the removal test tomorrow.

Thanks once again Jim...you're a life saver!

Bad CTS
 

JimF,

I had the CTS tested today while I was at the inde shop and you were apparently once again correct. It read 181 ohms at 83 degrees. According to the Alldata sheet they showed me, it should be reading around 300 ohms or so at that temp. So, it looks like my CTS is just reading the temp too high.

I wonder how many other people who THINK their 140 is running hot actually just have a bad CTS???????

I just emailed Philip in the parts shop to get a price on a new one. I think I can handle that job myself! ;)

Thanks again. You are THE MAN!

<<I wonder how many other people who THINK their 140 is running hot actually just have a bad CTS???????
>>

You are talking a different sensor

CTS sensor has nothing to do with the gauge sensor .
And the gauge sensor specs are :
60C-110 ohm
80C-67 "
100C-38 "

Thanks
 

Thanks for setting me straight on that Arthur. I just assumed that the guage got it's info from the the CTS. Oh well, you know what they say happens when you assume....

Thanks again!

I'm not sure we all are. . .
 

straight!

The CTS is the B10/8 sensor; that's what I call it; the ECT is B11/2. Check the picture on my page under MENU#18; clearly shows both sensors.

The ECT sensor (B11/2) temperature vs resistance readings are:
Temp(C)--Temp(F)-------- Ohms
20 --------- 68 ----------- 2500
30 --------- 86 ----------- 1700
40 ---------104 ----------- 1170
50 ---------122 ------------ 830
60 ---------140 ------------ 600
70 ---------158 ------------ 435
80 ---------176 ------------ 325
90 ---------194 ------------ 245
100 ------- 212 ------------ 185

The reistance of this sensor should be within +/-5%. Again this is the ECT sensor.

The CTS (B10/8) sensor's temp vs resistance characteristics are different from the B11/2 sensor. But the key values for this sensor's resistance is the resistance value at 100C, 107C and 115C.

For 100C, the resistance sb 310 ohms;
For 107C, the resistance sb 250 ohms;
For 115C, the resistance sb 200 ohms.

At these resistance settings, the fans should come on at low speed (310 ohms); second speed (250 ohms) and high speed (200 ohms).

For your '93 500SEL (W140): If your CTS sensor (B10/8) reads 183 ohms at 80C, it is BAD! Also if your ECT sensor (B11/2) reads 183 ohms at 80C, it's bad also.

This assumes it was read correctly. Hard to see why it's that low: normal failure mode for this device (varistor) is going to HIGH resistance.

Here's the "skinny"
 

JimF,

Once again, you are dead on. I have the ALLDATA sheet the inde printed for me in my hand right now. It is called "Coolant Temperature Sensor: Description and Operation". Under "Purpose and Location" it reads "The coolant temperature sensor (B11/2)........" The second page of this sheet has the temp and ohm chart listing the proper readings. They are exactly as you described. If you remember the A/C TDCs I posted, I had an E0 43 - A/C system coolant temperature sensor (B10/8), open or short circuit ** error. I asked the inde to check this out. (I faxed them a copy of the TDCs, so I know they had B10/8 in black and white). What they tested was, apparently, the ECT sensor (B11/2), not the CTS (B10/8). I looked at the title of the ALLDATA sheet, saw Coolant Temperature Sensor (CTS?) and thought they had tested the right one. Sounds as if both may be bad. My gut tells me that neither of these could be very costly, so I think I should probably just replace them both and have some peice of mind.

I'm going back to the inde tomorrow afternoon to get this straight. You have been a lifesave Jim!

Hope my ignorance hasn't put anyone else on the wrong track with their problem!

I would make sure that . . .
 

somebody who reads those sensors that can properly operate a ohmmeter, even if you have to do it yourself. If you not able, maybe you can enlist the aid of a neighbor.

The easiest way is to start 'cold'; just watch the temp gauge and take some readings at easy points: 60, 80, 90, 100C. As you know, 90C is halfway in between the two lines that mark 80 and 100C on the temp gauge.

The most important are the readings at 80, 90 and 100C. They should be close to what the table says. If way off, then r&r the sensor (B11/2).

Do the same thing for B10/8 and watch for the readings around 100C. Remove the Cool Harness for this testing. BTW, you probably have to close the hood to try to get it to 100C.

If the SENSORS are ok, then you may need to test the car's electronics. Mercedes recommend the use a resistance substitution 'box' (rsb).

To test the AUX FANS operation: Remove the cable that connects to the B10/8 sensor and hook-up the rsb.
1) Set the resistance to 310 ohms. The fans should come on 1st stage (low).
2) Set the rsb to 250 ohms: fans should come 2nd stage.
3) Set rsb to 200 ohms; fans should be on high.

This testing can be done with discrete resistors: select/test to make sure that they MEASURE very close to the three values: 310, 250, 200 ohms. Just clip them across the B10/8 leads.

Then let us know what happens.