Twin speed fan always on regardless of water temp

[scoobydo]

Hi I have a 333i that the fan is always running as soon as IGN I switched on. At the bottom of the rad are two temp switches these both read open circuit. However the wiring that goes to the switches on one of the switches has a dead short. Anyone got any ideas? Fan does go to fast speed eventually so one is definitely working. This needs fixing as the car takes an age to warm up and is probably also making the cold running enrichment to stay on longer than required which ain't good on the pocket.

Thanks

[Brianmoooore]

First of all, the fan being on shouldn't significantly affect the engine warm up time. Check the engine coolant thermostat for this.
As for your 'short', that could be anywhere and anything. Has it always done this? What happens if you pull out the low speed relay?

[scoobydo]

Thanks, here is an update if I pull the low speed relay then fan stops. Have tried to swap low and high speed relays and it still is always on. Just took it out for a spin and it sits at below quarter. Also not so good in the winter months for the battery I guess. If I pull the fuse for the low speed relay fan also goes off, but strangely if I also pull the fuse 19 which looking at online guides is the mirror heating circuit then the fan goes off. Any Ideas please.

Thanks

[Billwill]

Have you disconnected the wires on the thermo switches and measured the switches to see if the low speed contact has welded together?

I don't suppose your 333i has an aircon? If it did then the low speed relay would also get power from the aircon ON button.

I do not have 333i diagrams...my 325i diagram shows that fuse 19 is the fuse that directly supplies +12 volts to the common on the thermo switches (Green/Black wire?)

[scoobydo]

yes have air-con and power steering, not original fit aircon though. My aircon has two condensers behind the drivers lamps with separate fans for them. Yes switches are open circuit but the wiring to one of them has continuity between the two wires.

[Brianmoooore]

With OE aircon, the feed that switches the low speed fan on when the aircon is turned on comes from fuse 20, but if the low speed fan is switched on by the thermo switch, the power comes from fuse 19. Of course, with your non OE system, this might not apply.
As you've probably worked out for yourself, fuse 19 feeds the coil of the low speed relay and this feed should be via the lower temperature part of the thermo switch, but in your case is somehow bypassing it.

[scoobydo]

This is a pain. Ok in the summer to stop heatsoak as the rad is very small but this time of year it is very noticeable. Is it an easy job to re-wire from the thermoswitch back to relay not the physical running of cable but getting to underside of relay. Note I have two thermoswitches rather than the single 3 cable one so in effect I have 4 wires. Car seems much happier if a bit more temp gets in there.

cheers

[Brianmoooore]

Easy enough to get at the underside of the relay. One screw outside the fusebox, one visible one inside the box, and one hidden under a relay. Don't touch the hex. cap bolt!
The top of the box will still be held down by the mass of wires connecting to it, but can be eased up enough to work on it. I would expect any second connection to the relay to be right at the pin itself. I.e. Two wires soldered onto the relay socket.
I still think you should check the water thermostat in the engines outlet elbow.

[scoobydo]

Ok will have a look to see if I can work out what is going on. Will see what voltage is at the ECU to check if enrichment is happening when not wanted/needed and perhaps adjust to suit the fault.