Mercedes-Benz Forum banner

1 - 11 of 11 Posts

·
Registered
1966 230S, 1991 560SEL
Joined
·
56 Posts
Discussion Starter #1
I would like to add a switch for the auxiliary fan on my 1991 560SEL. In the Florida Heat and AC and Traffic I would just like to be able to switch it on when I feel like it should be on.
So how would I best go about it, which wire do I tap into?

Thanks
 

·
SuperModerator
1986/1990 W126
Joined
·
14,461 Posts
It's super easy. The info is pictured here on the forum already somewhere but you just take the wires from the receiver drier I think it was. I ran wires from there through the grommet on the firewall and put a switch in the glove box.
 

·
Registered
One Smoke Silver '87 570SEC, one Black Pearl '87 560SEL
Joined
·
4,505 Posts
Here in Las Vegas (supposed to be 112F today) I put a resistor across the sensor on the thermostat housing. The aux fan now comes on in the high 80's engine temp and it does fine keeping the AC working and the engine a little cooler. I thought about a switch, this is exactly what a lazy guy needs...

In the picture I have a 730 ohm resistor installed because that's all I could find at the moment and it gave me the 80's "on". The recommended size is 1,100 ohms for about 100C "on".
2644469
 

·
Registered
1989 300SE 232k miles
Joined
·
1,546 Posts
Here in Las Vegas (supposed to be 112F today) I put a resistor across the sensor on the thermostat housing. The aux fan now comes on in the high 80's engine temp and it does fine keeping the AC working and the engine a little cooler. I thought about a switch, this is exactly what a lazy guy needs...

In the picture I have a 730 ohm resistor installed because that's all I could find at the moment and it gave me the 80's "on". The recommended size is 1,100 ohms for about 100C "on". View attachment 2644469
This is at the sensor/switch for the engine temperature, right? Vs down at the AC drier?

It seems to me doing this at the engine temperature is a better set up.
 

·
Registered
1985 500sel and 500sec 2012 E63 1989 Porsche 911
Joined
·
5,444 Posts
whats interesting on my SEC (which its only running at 95/100C all the time no matter what) ive jumped temp sensor switch to have the aux fan run at all times, and i does nothing to the over all temp of the car.

from the ac drier side ive determined with great assistance from there that the pre resistor is bad. Ineed to get that sorted first and then ill look to doing a switch from that side .... i guess just to have it
 
  • Like
Reactions: isthenew

·
Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
Joined
·
4,768 Posts
whats interesting on my SEC (which its only running at 95/100C all the time no matter what) ive jumped temp sensor switch to have the aux fan run at all times, and i does nothing to the over all temp of the car.

from the ac drier side ive determined with great assistance from there that the pre resistor is bad. Ineed to get that sorted first and then ill look to doing a switch from that side .... i guess just to have it
Too bad about the aux fan resistor.. I think if you remove left section of the false firewall you'll likely get more access to the area underneath the brake master cylinder..
That's my hope for you anyways.. All the brake lines, wires & such have dedicated multi avenue grommets that stay in place when that panel is lifted.. so not too too bad at all.

In addition, I think your car's coolant temperature would probably benefit from swapping to an R107 75C or a Gen2 80C [Using your Gen1 t/stat seal in either case] from the 84C Gen1 'stat that is in there now. The thermostats are the same diameter, and the only thing is to make sure the bypass valve is the wide type, close to the T/stat body as in the pictures.
With that 'tweak' I think you'll see a good result straight away, especially if the 75C 'stat is chosen 116 200 00 15
There are pictures of Wahler & Mahle-Behr offerings on this page:
* As an aside, Gen2 can use either the long or the short versions as they mount differently. I have used both configurations in my 1991 M116.965 engine with good results.

Hang in & stay safe

M

IMG_2768.JPG IMG_3586.jpg
 

·
Registered
1989 300SE 232k miles
Joined
·
1,546 Posts
I’m going to add, if the new thermostat comes with 2 gaskets, you only need to use one. ...as I found out when I cracked the thermostat housing trying to get both to fit 🤦‍♂️
 

·
Registered
1985 500sel and 500sec 2012 E63 1989 Porsche 911
Joined
·
5,444 Posts
test that 75 stat in a pot of water before u install it...remember i did that and they both opened at 84... just saying
 

·
Premium Member
1999 500SL, 1988 SEC
Joined
·
1,349 Posts
Yes I also would install a rheostat inside the passenger compartment instead of an on off switch for the aus fan. That way you could adjust what temp the fan comes on at. You don’t need it all the time and if its on it causes unnecessary wear
 

·
Registered
1991 560sec. 1991 560sel 1969 280SL
Joined
·
1,324 Posts
Yes I also would install a rheostat inside the passenger compartment instead of an on off switch for the aus fan. That way you could adjust what temp the fan comes on at. You don’t need it all the time and if its on it causes unnecessary wear
[
These fan motors are not designed to run all the time and would wear out the motor bearings, if set up that way. That happened to me on my 1985 500sel back in 1998 after I didn’t realise the temp sensor on the thermostat housing was internally shorted causing the auxiliary fan to run any time the engine was running. On the Gen1 the system is set up so as to turn on the auxiliary fan any time the engine coolant temperature sensor develops a fault.
 

·
Registered
1989 300SE 232k miles
Joined
·
1,546 Posts
[
On the Gen1 the system is set up so as to turn on the auxiliary fan any time the engine coolant temperature sensor develops a fault.
Given the aux fan runs when the sensor is unplugged on my 1989 300se, I’d say it’s the same for the M103 engine, regardless of the generation.
 
1 - 11 of 11 Posts
Top