Rad fan elecrtical issue

[donslade]

Ok, I've searched the forums, I've searched my Bentley manual and the BMW service CD, and I'm stumped.

Here is the problem and what I have done:

Rad fan will NOT turn on during normal operation (no hi/lo speeds).
Rad fan WILL cycle on/off with the AC compressor when AC is on
Rad fan WILL run both hi/lo speeds when rad fan switch on radiator is bypassed (shorting terminals per Bentley manual).
Checked for B+ voltage at black/green wire per Bentley manual. B+ voltage present.
Rad fan switch on radiator replaced with new switch, tests good. No change.
All fuses are good, both relays test good, swapped relays for new ones, swapped fuses for new ones.
All harness connections test good (fan to harness, rad fan switch to harness, fuses and relays to harness).

Any ideas?

[zoner]

Does the temp. gauge ever go past half way (12 o'clock) under normal driving? If not, it might just be that you're not getting the car hot enough to need the fan. I live in So. Cal. and it's pretty rare that my fan kicks on under normal driving conditions.

[bazar01]

Originally Posted by donslade

Ok, I've searched the forums, I've searched my Bentley manual and the BMW service CD, and I'm stumped.

Here is the problem and what I have done:

Rad fan will NOT turn on during normal operation (no hi/lo speeds).
Rad fan WILL cycle on/off with the AC compressor when AC is on
Rad fan WILL run both hi/lo speeds when rad fan switch on radiator is bypassed (shorting terminals per Bentley manual).
Checked for B+ voltage at black/green wire per Bentley manual. B+ voltage present.
Rad fan switch on radiator replaced with new switch, tests good. No change.
All fuses are good, both relays test good, swapped relays for new ones, swapped fuses for new ones.
All harness connections test good (fan to harness, rad fan switch to harness, fuses and relays to harness).

Any ideas?

The DME has an influence on the radiator fan operation when the AC is OFF. Check the prints. I had to bypass this and just ran it just thru the rad temp switch and straight to the fan relay in the fuse box.

[dave45056]

The DME get's its temp signal from the sensor on the side of the head (right next to the oil filter cap). On early models there are 2 sensors (one for the temp guage and one for the DME). On late models the functions are combined ito one sensor. Not sure what year car we are talking about here, but this temp sensor could be faulty.

One more thing... have you verified the system is bled properly? All of these sensors are immersion type sensors and will not read the proper temp when not in liquid.

[Noneone2]

I am having sort of the same problem. I am able to get the fan to run at high speed per the Bentley manual but not at lo/normal speed. I've replaced both radiator switch and the cylinder head sensor (only 1 in a '97 m44), also replaced the lo speed relay, thinking of replacing the hi speed as well. The system has been bleed well and the heater vents will fry. The fan only kicks on with the ac. The temp needle sits 1/2 a hair past 12 while driving but creeps up after a few minutes at idle and the fan never kicks on. I'm in toasty S Fl and don't want to melt the engine.

[bazar01]

Originally Posted by Noneone2

I am having sort of the same problem. I am able to get the fan to run at high speed per the Bentley manual but not at lo/normal speed. I've replaced both radiator switch and the cylinder head sensor (only 1 in a '97 m44), also replaced the lo speed relay, thinking of replacing the hi speed as well. The system has been bleed well and the heater vents will fry. The fan only kicks on with the ac. The temp needle sits 1/2 a hair past 12 while driving but creeps up after a few minutes at idle and the fan never kicks on. I'm in toasty S Fl and don't want to melt the engine.

I had the same issue on my daughter's 1996. Drove me crazy tracing the issue. I just removed the DME input by running a jumper wire from terminal 85 of the normal speed fan relay direct to the low temp contact on the double temp switch. The radiator fan low speed has been operating flawlessly since then.

Refer to the red line in the diagram.

[Noneone2]

Pm'd

[donslade]

Update:

I rechecked the old rad dual temp switch and found the ground terminal was bent and not making contact. The new switch is good. But the fun continues.

1. I replaced the water pump and thermostat just to be safe. I thought the WP was original to the car but they had been replaced in 2008 when the burst plastic water pipe was repaired. They were not listed as replaced in the repair receipt from the garage!
2. Using an OBD2 bluetooth interface and Torque software running on my phone I have been monitoring temps for the last several days. The temps reported by the ECU will get to 105C (221F) before the cooling fan turns on. The temp at the rad dual temp switch at this point is about 82C (switch is supposed to be 80C for low and 88C for high, measured with a cheapo infrared thermometer). When the fan turns on the coolant temp drops to around 100C within 1 minute. Ambient temp here has been ranging between 95 and 105F (35 to 41C) during the day.
3. I have tried to ensure that there is not air pockets in the system by bleeding while the front of the car is elevated. I am not getting any air out at the bleed screw on the rad. So far so good.

So far everything seems to be operating as designed. I am still a bit concerned about the temps reported by the ECU but until now I have no historical data to compare to. The temp gauge stays at the center position even though the coolant temp reported by the ECU ranges from 85C to over 105C. I guess that is what it is programmed to show.

I'll keep monitoring this for a while. Very easy to do with the bluetooth OBD2 interface.

Thanks

[BlackBMWs]

Hi Don!

I know this is an older thread, as I a researching inconsistent operation of the fans on my 97 M44. On startup, the fan will turn on at around 105c the first time, drop temp, then not start up again. I've had the temp rise to 120c (3/4), before I either turn on the A/C to force the H/S fan to engage or just shut her down.

I've swapped relays, bench tested the fan for low/high speed operation and also observed using a OBD II BT device.

I will pull the rad sensor connection and jump test the T1 and T2 to ground connections to see if the L/S H/S fan works from there.

I'm looking for some consistency as far as fan activation and it is very inconsistent. As we move into the 100+ summers out here, I want to confirm the cooling system is fully addressed.

How'd your issue play out over time? Thanks!

Originally Posted by donslade

Update:

I rechecked the old rad dual temp switch and found the ground terminal was bent and not making contact. The new switch is good. But the fun continues.

1. I replaced the water pump and thermostat just to be safe. I thought the WP was original to the car but they had been replaced in 2008 when the burst plastic water pipe was repaired. They were not listed as replaced in the repair receipt from the garage!
2. Using an OBD2 bluetooth interface and Torque software running on my phone I have been monitoring temps for the last several days. The temps reported by the ECU will get to 105C (221F) before the cooling fan turns on. The temp at the rad dual temp switch at this point is about 82C (switch is supposed to be 80C for low and 88C for high, measured with a cheapo infrared thermometer). When the fan turns on the coolant temp drops to around 100C within 1 minute. Ambient temp here has been ranging between 95 and 105F (35 to 41C) during the day.
3. I have tried to ensure that there is not air pockets in the system by bleeding while the front of the car is elevated. I am not getting any air out at the bleed screw on the rad. So far so good.

So far everything seems to be operating as designed. I am still a bit concerned about the temps reported by the ECU but until now I have no historical data to compare to. The temp gauge stays at the center position even though the coolant temp reported by the ECU ranges from 85C to over 105C. I guess that is what it is programmed to show.

I'll keep monitoring this for a while. Very easy to do with the bluetooth OBD2 interface.

Thanks