'73 3.0CS wiring help needed

[CTD]

Hi everyone,

I spent today fixing and replacing some wiring around the engine area.
I found this auxiliary fan in front of the radiator without any wiring connected to it. I tested the fan and it worked.

Now I tried making it functional so here is what I did.
I took a NOS relay I had lying around and made these connections:

Pin 30: Fused wire to the battery
Pin 85: Engine temp sensor (to which the temp gauge in the dash is also attached)
Pin 86: positive wire from horn relay (accessory power)
Pin 87: positive wire to fan

Fan negative wire grounded on the chassis.

Now, for some reason, the temp gauge on the dash doesn't work, as long as pin 85 on the relay is connected. The fan turns on when the temp sensor is trigered and turns off after it's cooled down. So that's working ok.

Can anyone explain why the temp gauge on the dash isn't working when everything is connected?

Kind regards, Tom

 

[Belgiumbarry]

Tom , the gauge sensor is changing Ohms with temperature to give the gauge a "indication". You can't use this one for a fan.
For a fan you need a extra sensor , a on-off one at a certain temperature. It just switch on or off at that temperature , no Ohms gradually.

 

[autokunst]

I have a theory, but no solution. I believe the temp gauge in your dash measures the voltage potential between the engine temp sensor and ground - the value resulting in the needle reading a temp on the gauge. Adding Pin 85 to this circuit is likely changing the voltage potential and causing the gauge to be outside its parameters. It would be adding the inductance/impedance of the coil in the relay to the measuring parameters of the gauge. That is a guess, and as I said, I don't have a solution. But maybe someone else will build on my theory with a suggestion of what to do??? Best of luck, regardless.

And as I typed I see the solution is to use a separate sensor, so as not to interfere with the electrical circuit I outlined. Brilliant!

 

[CTD]

Thanks for the response! Is there another place to add a temp sensor? I have read that some coupes have a sensor in the radiator but mine hasn't.

 

[teahead]

http://www.iemotorsport.com/bmw/item/E28thermohousingkit.html

https://e9coupe.com/forum/threads/thermostat-housing-with-extra-ports.24227/

 

[CTD]

http://www.iemotorsport.com/bmw/item/E28thermohousingkit.html

https://e9coupe.com/forum/threads/thermostat-housing-with-extra-ports.24227/

And this works Plug&Play?

 

[Markos]

Tom,

Are you sure it isn’t the factory AC aux fan?

 

[Belgiumbarry]

Tom , you can get that from W&N ... as i did . They have also nice plugs for the openings you don't use. ( you use 2 , gauge and fan switch sensors)
don't forget to order also the gasket and the dedicated thermostat for that type housing.

https://www.wallothnesch.com/motorteile-kuehlung/bmw-2-5-cs-3-0-csl-e9/katalogbild-11-26.html

 

[autokunst]

I used BMW part number 11 53 1 710 959, which fit right on the engine and has extra ports for sensors.

 

[autokunst]

Are you sure it isn’t the factory AC aux fan?

Does it look like this?

 

[Belgiumbarry]

don't forget to inspect also the thermostat cover first .... look at what i found !

https://e9coupe.com/forum/threads/1970-2800cs-restoration.27508/page-2

 

[CTD]

Does it look like this?
View attachment 45809

The fan itself looks like that. But the bracket is very different.

 

[OCCoupe]

Yours is a later factory fan with a shroud. This is correct for a 73. If your car had factory air then it would have come with this fan. The later 1974 radiator has a provision at the bottom hose fitting for a temp sensor which you can wire to your fan, as well as for then the A/C compressor turns on.

 

[Ohmess]

CTD -- here is a wiring diagram for the air conditioning:

This list references the items in the diagram:

Your fan (#13) should be powered by a separate wire, incorporating a flying fuse (#7), that runs along the nose of the car to a relay (#9) on the right fender wall. This power wire runs to terminal 30 on the relay, with output on terminal 87 to the motor and the other motor wire to ground. The relay is initiated by the fan switch (#10), which initiates the compressor clutch (#12, subject to the temp switch (#11)) and turns on the fan(#13).