Aux Fan

[rishabhb]

Car is a 1975 530i. Did not come with factory A/C. I have replaced the temp switch on the rad for the aux fan. There are 2 connections on the thermo switch which are connected. Additionally, there are 2 wires with spade connectors, one of them going to the switch and the other one to the aux fan. When i connect the 2 wires the fan comes on. But it stays on all times when the car is switched on.

I was idling at a drive-thru today and temp started climbing, but the aux fan did not come on. I am under the impression that it should come on.

My fan clutch is good, bled the air from cooling system and car runs solid at half mark all times. But when it was rising i was hoping the aux fan would be triggered.

Does anyone know what those 2 wires are supposed to do and how the aux fan works in general?

Thanks.

[tlake]

From what you said it sounds like the car has a/c, but didn't come new with factory a/c My understanding is the aux fan is for the a/c condenser, and only comes on when the a/c is turned on. The aux fan's job is to expel heat from the a/c condenser. For the car's cooling system radiator you have the main engine driven fan.

[rishabhb]

The car does not have A/C. But i was surprised to see it has an aux fan.
Unless the A/C was removed by PO. There are no A/C lines at all and has the old school vents which are fixed and airflow direction cannot be adjusted.

[Lock]

The aux fan has two speeds, half and full. I don't know what non-AC cars have, but factory AC cars have two themo switches, one for 90C and one for 99C, with two sets of wires for each. The 90C triggers half speed, and the 99C triggers full speed. Also, when the AC compressor is on, it triggers the fan at half speed.
These thermo temperatures are above typical operating temperature, M30 thermostats are around 75-80C opening.
The aux fan is not designed to regulate temperature like in a modern car, it's only additional airflow for high temperature protection. The clutch fan is supposed to regulate the temperature so if your fan clutch is old it may not be spinning fast enough at idle. If the radiator coolant temps are hitting 100C then the engine is way too hot.
How far did your temperature go up during idle? 3/4 or into the red? The aux fan will come on when you go into the red. Also, what is the temperature rating of the thermo switch you installed? You can install lower one like 80C if you want, but I'd recommend ensuring the fan clutch is healthy.

[rishabhb]

The aux fan has two speeds, half and full. I don't know what non-AC cars have, but factory AC cars have two themo switches, one for 90C and one for 99C, with two sets of wires for each. The 90C triggers half speed, and the 99C triggers full speed. Also, when the AC compressor is on, it triggers the fan at half speed.
These thermo temperatures are above typical operating temperature, M30 thermostats are around 75-80C opening.
The aux fan is not designed to regulate temperature like in a modern car, it's only additional airflow for high temperature protection. The clutch fan is supposed to regulate the temperature so if your fan clutch is old it may not be spinning fast enough at idle. If the radiator coolant temps are hitting 100C then the engine is way too hot.
How far did your temperature go up during idle? 3/4 or into the red?

It went slightly over the half mark

The aux fan will come on when you go into the red. Also, what is the temperature rating of the thermo switch you installed?

I'll check on that

You can install lower one like 80C if you want, but I'd recommend ensuring the fan clutch is healthy.

[keehn]

Rishabhb,

You didn't mention the temperature outside while you were idling, but it might be possible that your radiator or elsewhere in your coolant passages are blocked to varying degrees.

Also, if you are still using the OEM brass radiator, you may want to seriously consider upgrading to the E28 aluminum radiator. It's a simple upgrade http://firstfives.org/rad.html that gives you far greater cooling capacity than the OEM brass setup.

Also, not sure how you ensure zero air pockets in your coolant channels, but a tool like the Schwaben coolant vacuum fill tool https://www.ecstuning.com/b-schwaben-pa ... 948sch01a/ or other competitor (Harbor Freight even sells a version) will make filling coolant FAR, FAR easier. I have a Schwaben and have filled many cars with it. I don't have to bother with bleed screws, plus I can also test the coolant system for leaks; pull a vacuum, close all the valves, and wait 5-10 minutes to see if the vacuum holds.

Anyways, just my .02 cents.

Mike

[tlake]

I think the aux fan on non a/c e12s could be a North American thing. I have seen pics of Euro cars sans a/c, and they don't have the extra fan, not even e28s.

Given the 530i got factory a/c standard from 1977, and you are likely to be using a/c on a warm day anyway, I guess the window of the aux fan coming on independently of the a/c is a small one.

[rishabhb]

I have a new Rad. Its OEM Brass but new.
Temp was around 20C outside.

I bled using the bleeder screw on the T-Stat.

I think i might have a bad ground issue. The temp needle rocks when i have my flasher on, much like an ammeter would.

Aux fan might well be a NA thing. I might just wire a switch to turn it on when i really need to.

[Robert Bondi]

Start with checking the grounds if your temp needle is flickering.

These cars were notorious for running hot, even when new. Check the cooling system FAQ
that covers everything I did to make the car reliable for a Texas climate.

My Euro 528 has no aux fan and no A/C....yet.

Two things trigger the aux fan on my 77 530i: A/C compressor clutch and temperature switch
in the radiator. Later E12s started using two temperature switches.

I've independently calibrated the temperature gauge. Each tick is about 10 C: 1/4 is 70C, 1/2 is
80C, etc.....

The thermostat and temp switches can be bought at different temperature specs if you want
to change your default operating conditions.

[tlake]

I have a new Rad. Its OEM Brass but new.
Temp was around 20C outside.

I bled using the bleeder screw on the T-Stat.

I think i might have a bad ground issue. The temp needle rocks when i have my flasher on, much like an ammeter would.

Aux fan might well be a NA thing. I might just wire a switch to turn it on when i really need to.

Rishabhb, Does your car still have the thermal reactors, or are they long gone Wiring in a dashboard switch for the aux fan sounds a good idea.

[rishabhb]

Thanks for all your input. I will fix the ground.

Thermal reactor and EGR has been deleted.