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1997 E420
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37 Posts
Discussion Starter #1
Ok, I've searched and searched...cant find the exact info I need...wondering if any of you all are in the charitable mood? ;-)

It think my 1997 E420 has the fairly common "faulty temp sensor" thing where a) the cars temp is normal at highway speed, b) runs up to overheating if sitting still.

I am not certain that the electric aux radiator fans even work anymore because they never seem to kick in...but instead of replacing them, I would guess this is a sensor issue?

So, help me out with this:
1) for this car, does the ECT sensor fulfill the responsibility of switching the aux radiator fans on/off?
2) what is the part number for the ECT?
3) How many ECTs? 1 or 2?
4) for this engine, where are they located?
5) Anyone know of an online parts dealer that carries these?

Also, anyone know how to test the fans to see if they work by perhaps bypassing or overriding the ECT (assuming the ECT actually controls them of course)??

My appreciation in advance,
shage1966
 

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1997 Mercedes-Benz E420
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139 Posts
the auxilary fans on these cars have been known to kick the bucket especially now since these cars are getting old (being 13 years now), the only way to get it working again is to replace the whole fan assembly or the driver's side one with the motor, and while youre at it i would suggest a new belt as well.
 

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1997 E420
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37 Posts
Discussion Starter #3
I'm thinking of running a bypass power lead to the fans to see if, given some DC, they fire up. I would rather not replace the fans unless I know they are the problem. in the couple years I do know that the fans would come on at temperatures that I would think are higher than they are supposed to, so I've been suspecting a sensor malfunction for a while...though your point is good: I suspect I might replace the sensor(s) and then in a few months replace the fans because they are 95% into their life span.

Now, if I could figure out what the best way to get in that super-tight engine compartment, find the sensor, and pull it out! ;-)
 

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1996 210.020
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3,972 Posts
Are you in the US? Do you have automatic climate control?

If so, first run the fan test mode by holding both AUTO buttons down for >10 seconds. My car seems to take about 12 or so. This should set the system for full auxiliary fan demand. If the fan does not run, watch it carefully to see if it twitches every few seconds. If it does this twitching (and you can see it on a connected voltmeter), the problem is very likely a bad motor. If it doesn't do any twitching, yet you can see it on a voltmeter, it is almost certainly a bad motor. If it doesn't do any twitching and you can't see any voltage fluctuations on the wires, it is probably a bad controller.

Running a 12V lead to the fan motor is not a valid test; if it runs with 12V, it does NOT mean that the motor is good. This fan control is not a simple relay and ballast resistor.

If you have a sensor malfunction, your gauge will show the wrong value. Are you suspecting that the car is not really getting hot?
 

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E-Class 300 TD 1998, E-Cllass 290 TDi 1996, 601 DKB 1982(207D)
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117 Posts
I also have the same problem, albeit that I have not found the solution yet.
But I do know that there is a temp-sensor and a pressure sensor on the dryer of the airco. Above a certain temp and/or pressure is should switch on. My fans do work in the override mode by pressing the auto-buttons as indicated above, but they do not automatically switch on. In am planning to check the relais now, which should be located below the left headlight, basically the same location as the dryer. The access to this should be provided by removing the left head-light.
I have noticed that the hoses for the headlight washing system have been repaired in a somewhat stupid way. It could very well be that due to this the cables for the sensors on the dryer are loose or damanged.

Some people say that you can remove the temp-sensor if it appears to be faulty...others say that prior to this the airco should be vacumized and emptied...what is true.

I do not have a problem with a engine getting too warm, at least not now with the averages still being below 20 degrees centigrade. My visco engine fan produces enough ait I guess for now.

BTW...the Car is a W210 E300 TD 1998

Cheers,
Ingmar
 

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1996 210.020
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On my '96, you must depressurize the system prior to removing the temperature sensor. Its hole is not blind, but goes into the refrigerant path.
 

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E-Class 300 TD 1998, E-Cllass 290 TDi 1996, 601 DKB 1982(207D)
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That was my assumption as well, judging by the looks of it. I do think that the place where it has been mount, just below the reservoir for the windows, is not the smartest place. The location is very likely to get wet from spilled spraying liquid. So there is a chance that it will also be a bit corroded.

Cheers,
Ingmar
 

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E-Class 300 TD 1998, E-Cllass 290 TDi 1996, 601 DKB 1982(207D)
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Ok...wouldn't have expected otherwise, having the quality standard of MB connectors in mind. What I did notice is that the hoses for the headlight-washer have been arranged quite messy, perhaps that has damaged the wires...
It is done in such a way that I do not have the impression that it has been done by an official MB dealer. I will have a look to it and post about it with pics.

Cheers,
Ingmar
 

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E320/E250 Bluetec Ford F350 6.7l
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36,199 Posts
I know those fans are controlled by pretty funny way and not connected directly to AC. When I replaced radiator, I lost a nut holding the fan, what made the blades rubbing the grill. Having to go in cold weather I took off assuming those fans will not be activated.
About 20 seconds into the drive, with engine still cold I hear the fan rubbing the shields and had to pull the plug to stop it from turning.
So as far as I am concern, if you know the motor is good, you need to run full diagnose test on clima to find the problem.
Than placing components in the car can't be always done with practicality in mind. Besides computer under the gear shifter/cup holders in W210, the W163 has ABS unit mounted under windshield fluid reservoir. Prone to leaks 80 cents grommet cost $700 in ABS module replacement.
 

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1997 E420, 2002 C230 Coupe, Ford Expedition
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41 Posts
Please check if the fan starts at the moment you start the engine. If it does, replace the relay.
 

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1997 E420, 2002 C230 Coupe, Ford Expedition
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41 Posts
I have an issue with my E420 that everytime I turn the key, i could hear the aux fan start running but after few kilometers run, i could see the temperature rising but I don't hear the fan kicking. I thought i need to overhaul my clutch fan but was fixed when I replaced the relay.
 

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1996 210.020
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I don't recall the figure, CR. I would have to look at the climate-control manual (or the FSM) again. It's pretty high though. At least 100C.
 

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2010 E350
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200 Posts
Temp Fan Relay

I have an issue with my E420 that everytime I turn the key, i could hear the aux fan start running but after few kilometers run, i could see the temperature rising but I don't hear the fan kicking. I thought i need to overhaul my clutch fan but was fixed when I replaced the relay.
Can you please tell me the location of the Temp Fan Relay.
thanks, donald
 

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2000 MB
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803 Posts
MattL,
Thanks for the method of checking the aux. fan. Pressing the auto buttons for 12 secs. Mine took 15 secs. and the aux fan came alive. Tell you frankly, I was worried for them a bit because I have never seen or heard them come on. It sounds good. Thanks.
 

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1996 210.020
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Can you please tell me the location of the Temp Fan Relay.
thanks, donald
It's not a relay, but...

It might be behind the left headlamp. It might be in the underhood fusebox. I think there's one more potential location but I can't remember where that is. A few different systems were used for this over the years.
 

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1996 210.020
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3,972 Posts
MattL,
Thanks for the method of checking the aux. fan. Pressing the auto buttons for 12 secs. Mine took 15 secs. and the aux fan came alive. Tell you frankly, I was worried for them a bit because I have never seen or heard them come on. It sounds good. Thanks.
Idle with the AC running on a hot day, and the fan will start (unless something is wrong). But it starts on very low speed at first, and that's often enough. The low speed is why you never hear the thing; it almost never gets to full demand unless you enter the test mode.
 

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1997 E420
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Discussion Starter #20 (Edited)
AHHH! I ended up replacing my thermostat....what a royal pain in the arse that thing is! Had to buy a 10mm racheting box end wrench for the one bolt hidden down behind that bugger (Husky brand seemed so much finer and believe me you need a very thin-walled wrench to fit...so I recommend Husky over Craftsman in this case). Also had to pull up (and bend) the dip stick tube to make it happen (the replacement job...that is). Then, had to play cat and mouse with the tiny hose and clamps....no fun. 30 mins of fussing and she finally went back on. I recommend this procedure:
1. With the old thermostat housing assembly off and the hose off, install the new thermostat housing.
2. Install the hose (without the ring clamps). 30 mins of fussing...I promise it is possible...though it doesn't look it.
3. install each of the two ring clamps AFTER the hose...so much easier that way.

Anyway, I got the new one installed.....and no luck!!!!!. Same problem: car runs cool while at speed...runs very hot (to 118C) while idling in traffic. Aux fans come on strong but don't seem to keep the temp down.

So, even with the fans running, a new thermostat, and a fresh coolant fill....car still overheats. Now then, after looking over and over and over at the duo valve problems...and the "air in the system" problems...and the "can the water pump ever spin but still not pump coolant?" discussions...and the "might have a leaky head gasket" scare talk, I decided to pay better attention to the primary cooling fan...and low and behold! the clutch is out! Well y'all, there's my problem. You all did help me so much...thanks a million billion!

Now I have to figure out how I am going to take that bugger off! Doesn't look like a job that's kind to the knuckles.
 
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