1999 540i electric fan wiring advice needed

[Flak]

Hi all. I recently acquired a 1999 540i and have been fixing up some neglected maintenance items that were passed over by the PO. One of which was the engine cooling fan. The fan clutch is FUBAR and I'm leaning heavily to an electric fan setup, to the tune of a 16" SPAL. I was hoping to use their provided fan control relay and hook it up to activate at the same time as the aux fan. In my previous car, I had an M52B28 that I was able to run the same setup, tapping the sensor wire for the relay into one of the wires coming out of the radiator temp sensor. It came on when I turned the AC on, as well as when the temp sensor activated it.

I've tried looking some different setups for the 540 and they're either using a T fitting in their radiator hose or some kind of external or manual temp sensor. Would I be able to wire it up through the same temp sensing wires that would kick on the aux fan, as it was with the e36's, or is it not as simple as that?

The posted diagram shows exactly what I did, using the sending unit (grey) wire tapped into that stock temp sensor.

[rf900rkw]

Sigh, yet another Z3M owner pops up in the E39 side with a 540. Welcome.


Simple answer. No.

Long answer. It's not an E36, no. The M62TU uses a computer controlled aux fan that comes on at 80C and ramps up quite nicely and quickly. If you want to install a second fan in a E36 fashion, you will have to emulate the E36 setup. This means putting a thermal switch in the radiator outlet tank or lower hose. If you set it to 91C like the E36, it will NEVER come on, but will give you a warm-n-fuzzy.

[Flak]

YUP. Z3 was awesome, but it quickly became less practical with highway commuting.

Welp, I was hoping there was a way around it, but oh well. Maybe it'll live off of just the aux fan for now.

[qcdstick]

I have my spahl fan set to kick on when the aux fan is on (any speed). I basically use this as my AC pickup to the fan control unit, so that the big fan assists when the AC is on or any time the car is calling for additional cooling. However, I also have it set to kick on based on a coolant temp sensor which I would consider to be the primary trigger. If you do it, make sure to use a relay so the voltage from the aux fan only serves to trigger the relay (very little draw), and not power anything directly.

[rf900rkw]

You have an M62, which is the E36 style fan. OP has a M62TU, totally different and computer controlled.

[Flak]

So I'm happy I kept my Z3's old fan clutch unit. It fits and still functions properly! That will do for now, but I really would like to put an electric fan in there.

So I did a little more intensive research about the TU aux fan setup and found this nice little tidbit of information:

Just an FYI to correct some of the info in the older portion of this thread.

The OP had a 2001 540i which would have had the M62TU engine, which used a variable speed aux fan. That fan doesn't necessarily turn on when the AC button is initiated. The variable speed fan turns on when it is sent a PWM (pulse width modulated) signal by the DME/ECU.

http://www.bimmerforums.com/forum/sh...7#post27242877

This confirms what you said about not being able to tap into the temp sensor or aux fan wiring.

[qcdstick]

You have an M62, which is the E36 style fan. OP has a M62TU, totally different and computer controlled.

Whoops, missed that. Thanks for the clarification.

[BMW540san]

I highly recommend Spal. Well over a year on both cars and no complaints. IMO, Auto Meter radiator hose adapter combined with Spal temp sensor is the best way to go when wiring Spal fan. Very accurate and every single component of Spal kit is high quality.
http://www.bimmerforums.com/forum/sh...on-97-BMW-528i

[vien]

I highly recommend Spal. Well over a year on both cars and no complaints. IMO, Auto Meter radiator hose adapter combined with Spal temp sensor is the best way to go when wiring Spal fan. Very accurate and every single component of Spal kit is high quality.
http://www.bimmerforums.com/forum/sh...on-97-BMW-528i

i see that you went with the 195 degree sensor but for a 540i you think the 185 would be ok? better alternator etc?

[BMW540san]

i see that you went with the 195 degree sensor but for a 540i you think the 185 would be ok? better alternator etc?

With 185F sensor, Spal fan would come more often and stayed on longer which does put stress on alternator. In my case, with 95C conventional thermostat, the Spal fan comes on at around 101 KTMP and stays on for about 15-20 sec til the temp drops to about 98 KTMP. That is the case if the car sits and idles. If the car is moving, Spal fan rarely comes on at all since the temp stays around 95C to 98C.
Just to clarify that we're on the same page, 195F sensor means that fan comes on if the radiator outlet temp reaches 195F and stays on till it cools down to 175F. KTMP or C is the temp at the engine outlet. In case of 185F sensor, fan stays on till temp drops down to 165F at the radiator outlet.

[vien]

With 185F sensor, Spal fan would come more often and stayed on longer which does put stress on alternator. In my case, with 95C conventional thermostat, the Spal fan comes on at around 101 KTMP and stays on for about 15-20 sec til the temp drops to about 98 KTMP. That is the case if the car sits and idles. If the car is moving, Spal fan rarely comes on at all since the temp stays around 95C to 98C.
Just to clarify that we're on the same page, 195F sensor means that fan comes on if the radiator outlet temp reaches 195F and stays on till it cools down to 175F. KTMP or C is the temp at the engine outlet. In case of 185F sensor, fan stays on till temp drops down to 165F at the radiator outlet.

gotcha gotcha so the best would be the 195 degree then so no strain on the alternator?

[vien]

any updates?

[Flak]

Yes! I decided to remove the clutch fan assembly entirely and live with just the auxiliary fan since I finally got a replacement for the shattered remains the PO left me. I'm just going to save up and use the setup that BMW540san suggested.

Now I have a new issue. The auxiliary fan is always on high, with or without A/C on and even if the car has just been started up after sitting all night. It's definitely the right fan too. I made sure I got the one for the TU engine and it matches the one I pulled out, albeit with the correct number of blades. I'm doing some research on what may be causing it, but if anyone has any insight on this problem I would greatly appreciate any help.

[ninetyseven1]

Yes! I decided to remove the clutch fan assembly entirely and live with just the auxiliary fan since I finally got a replacement for the shattered remains the PO left me. I'm just going to save up and use the setup that BMW540san suggested.

Now I have a new issue. The auxiliary fan is always on high, with or without A/C on and even if the car has just been started up after sitting all night. It's definitely the right fan too. I made sure I got the one for the TU engine and it matches the one I pulled out, albeit with the correct number of blades. I'm doing some research on what may be causing it, but if anyone has any insight on this problem I would greatly appreciate any help.

The aux fan is meant to cool off the A/c compressor not cool the engine
Put an electric fan on or use the factory mechanical fan.

- - - Updated - - -

Yes! I decided to remove the clutch fan assembly entirely and live with just the auxiliary fan since I finally got a replacement for the shattered remains the PO left me. I'm just going to save up and use the setup that BMW540san suggested.

Now I have a new issue. The auxiliary fan is always on high, with or without A/C on and even if the car has just been started up after sitting all night. It's definitely the right fan too. I made sure I got the one for the TU engine and it matches the one I pulled out, albeit with the correct number of blades. I'm doing some research on what may be causing it, but if anyone has any insight on this problem I would greatly appreciate any help.

Do yourself a favor and go to a junkyard and purchase a Ford Taurus 3.8L 2 speed electric fan, they outflow most aftermarket fans. They will flow past 3000 CFM! Should cost you like $50

[rf900rkw]

Either the fan is defective, power transistor shorted, or the computer is commanding max speed. The primary reason the computer would do this is a bad radiator outlet temp sensor, the sensor in the lower hose.


You'll be fine on just the factory electric fan. Cooling isn't about CFM. Cooling about airflow through the radiator. The factory pieces do it well.

[Flak]

The aux fan is meant to cool off the A/c compressor not cool the engine
Put an electric fan on or use the factory mechanical fan.

- - - Updated - - -

Do yourself a favor and go to a junkyard and purchase a Ford Taurus 3.8L 2 speed electric fan, they outflow most aftermarket fans. They will flow past 3000 CFM! Should cost you like $50

I was looking at the Taurus fan option as well but I'm leaning towards the SPAL setup due since I'd be using their temp sensor and relay anyway. I've used them in the past in a z3 and i like their product.

I haven't actually gone and removed the mechanical fan yet, so I guess I'll just leave it on, but the non functional clutch won't help it do much anyway.

[Flak]

Either the fan is defective, power transistor shorted, or the computer is commanding max speed. The primary reason the computer would do this is a bad radiator outlet temp sensor, the sensor in the lower hose.

You'll be fine on just the factory electric fan. Cooling isn't about CFM. Cooling about airflow through the radiator. The factory pieces do it well.

Would the outlet temp sensor be what gives the reading to the dummy temp gauge on the dash? Because that still works normally. I'll hook up a diagnostics reader tonight and see what temp it gives me.

[vien]

The aux fan is meant to cool off the A/c compressor not cool the engine
Put an electric fan on or use the factory mechanical fan.

- - - Updated - - -



Do yourself a favor and go to a junkyard and purchase a Ford Taurus 3.8L 2 speed electric fan, they outflow most aftermarket fans. They will flow past 3000 CFM! Should cost you like $50

is it 2 fans or 1 fan, would like to check this out ??

[rf900rkw]

No the gauge (it's a real gauge, BTW, BMW has very sound reasons for the behavior) is driven by the sensor on the thermostat. The sensor in the lower hose is purely for the cooling system control.

[Flak]

The lower radiator hose temperature sensor is what's causing it. It looks like it was damaged and the wires inside have been stripped out. The fan control is probably setting it to high as a safety precaution to prevent overheating in the case of a bad sensor.