Help please! Faulty radiator fan.

[bockercharlie]

 Engine overheated the other day after coming to a stop after 2 hours of motorway driving, coolant escaping out the expansion tank. Suspect because the radiator fan doesn't work, and I haven't heard it come on in ages! Changed the coolant temperature sensor, checked fuses and relays and applied power to the fan itself, which works. Any ideas please? 2004 Ford fiesta petrol, 1.4.

 

Thanks all!

[TomsFocus]

Have you checked the resistor that's on the fan cowling?  It's usually a cylinder shape with green insulation around it, on a triangular plug.

[bockercharlie]

Thanks so much for the help, I couldn't see one when I removed the fan the other day. Just had another quick look and am struggling to locate it. Help very much appreciated, I really need to fix this before summer

[bockercharlie]

This is what it looks like

[TomsFocus]

3 minutes ago, bockercharlie said:

Thanks so much for the help, I couldn't see one when I removed the fan the other day. Just had another quick look and am struggling to locate it. Help very much appreciated, I really need to fix this before summer

It's right at the bottom corner of the cowling.  If you didn't see it, it's possible that there isn't one on your model.  Though I have definitely replaced one on a 2003 1.4 petrol.  The design did change slightly but it's this green thing with a large plug that you're looking for.

[bockercharlie]

Just checked, mine definitely doesn't have that. When the car overheated and coolant was going everywhere, the temperature sensor on the dash still said normal/below halfway. I've never ever seen it get above that mark.

[TomsFocus]

1 minute ago, bockercharlie said:

This is what it looks like

Hmm, well, it doesn't look like it's there on your model.

[bockercharlie]

Just checked, mine definitely doesn't have that. When the car overheated and coolant was going everywhere, the temperature sensor on the dash still said normal/below halfway. I've never ever seen it get above that mark.

[TomsFocus]

2 minutes ago, bockercharlie said:

Just checked, mine definitely doesn't have that. When the car overheated and coolant was going everywhere, the temperature sensor on the dash still said normal/below halfway. I've never ever seen it get above that mark.

The dash temp isn't actually a live reading.  It's designed so that the needle stays roughly halfway over a large range of temps unless there's a problem...the idea is not to alarm the driver if the temp fluctuates a little during normal use...but personally I find the not knowing to be more alarming!

Do you have an OBD reader at all?  Either handheld or phone app?  They can usually show the real temp for the PCM input.  It's possible that the coolant didn't overheat, but just that the expansion cap has failed.  they're designed to hold a certain amount of pressure in which increases the boiling point.  A new cap is cheap and easy to replace.  Also check for any hairline cracks around the tank itself.  And ideally check for any cracks around the stat housing if you can see it.

Does your car have AC...and does it work?

 

[bockercharlie]

Car does have AC, but doesn't work. Coolant cap and expansion tank were both replaced six months or so ago. 

 

Yes I agree, I'd rather know exactly what the temp is doing. 

 

The only thing I can't get my head around is that now that I think about it, I haven't heard the radiator fan in ages and I'm sure I used to hear it quite frequently. 

[TomsFocus]

So do you have access to an OBD reader?  If you have Forscan, that might help us with a code for something cooling or fan related.  There's also possibly a fan test procedure to make sure the PCM can power the fan.  (I've done this with Peugeot software, can't remember if Forscan has the same function.)  I'm struggling to suggest anything else that you haven't already checked or tried now.

If you don't have access to any diags, you could bridge out the AC pressure switch (under the headlight on Mk6) which should bring the fan on immediately if the PCM is able to power it.  Should also power up the AC compressor though so don't run it for long if the AC system is low on gas.

 

[bockercharlie]

I don't have an OBD reader but might be able to borrow one! Okay I'll give that a look. It isn't worth replacing the thermostat then? 

[TomsFocus]

2 minutes ago, bockercharlie said:

I don't have an OBD reader but might be able to borrow one! Okay I'll give that a look. It isn't worth replacing the thermostat then? 

As the 'stat is such an awkward one on this engine, I wouldn't replace it just for the sake of it. 

If you can see any cracks/leaks around the housing, or if we can see that the temp is rising much past the stat's operating temperature via OBD (suggesting a stuck closed stat) then it would be worth replacing.

Regarding the OBD reader, if you can borrow or buy a Forscan adapter, that's much more effective than generic OBD.

[Paulkp]

Your AC might not work - but does the fan start if you turn the AC "On" ?

[bockercharlie]

3 hours ago, Paulkp said:

Your AC might not work - but does the fan start if you turn the AC "On" ?

Just tried, it does not.

Does this rule anything out/point to anything in particular?

Cheers

[TomsFocus]

2 minutes ago, bockercharlie said:

Just tried, it does not.

Does this rule anything out/point to anything in particular?

Cheers

No.  If we assume there's no gas in your AC system, the compressor isn't switched on as a failsafe.  With no compressor, there's no need for the fan.  If you bridge out the pressure switch (as mentioned in earlier post) and then switch on the AC with the engine running, that should bring on both the fan & compressor.

[bockercharlie]

18 minutes ago, TomsFocus said:

No.  If we assume there's no gas in your AC system, the compressor isn't switched on as a failsafe.  With no compressor, there's no need for the fan.  If you bridge out the pressure switch (as mentioned in earlier post) and then switch on the AC with the engine running, that should bring on both the fan & compressor.

Okay thanks very much, I'll have a look for the pressure switch as you say! 👍

[Paulkp]

I bow to Tom's superior knowledge !

Fan Relays are controlled by engine management, whether initiated by engine temp or AC I believe.

[isetta]

A temporary work around.  About 30 yrs ago my wife had a 1977 mk1 fiesta. It would overheat. The fan would come on but too late.  As a fix so we could use it I wired up a switch on the dash so I could manually switch the fan on and off.  Of course needs thick enough wire and high enough amp switch (or a relay) and fuse for safety.  But sometimes due to difficulty if finding fault or lack of parts to hand when you need a quick fix, this kind of fix (some will say bodge) saves the day

[bockercharlie]

14 hours ago, isetta said:

A temporary work around.  About 30 yrs ago my wife had a 1977 mk1 fiesta. It would overheat. The fan would come on but too late.  As a fix so we could use it I wired up a switch on the dash so I could manually switch the fan on and off.  Of course needs thick enough wire and high enough amp switch (or a relay) and fuse for safety.  But sometimes due to difficulty if finding fault or lack of parts to hand when you need a quick fix, this kind of fix (some will say bodge) saves the day

I did think about this, although not done it before, don't imagine it can't be that hard. Find a suitable wire/fuse, Hook it up to the battery, feed the switch into the cabin and tidy it all up right? Then just switch it on in traffic?

[isetta]

That’s the idea yeah. No idea how many amps it would use or exactly where to take the live supply from. Maybe from battery so you can keep it on for a bit after turning engine off?  Perhaps use a switch which has a light in it so it’s more obvious if you’ve left it on.

[bockercharlie]

On 3/30/2022 at 9:35 PM, isetta said:

That’s the idea yeah. No idea how many amps it would use or exactly where to take the live supply from. Maybe from battery so you can keep it on for a bit after turning engine off?  Perhaps use a switch which has a light in it so it’s more obvious if you’ve left it on.

I've looked into this for a bit and it seems fairly do-able. Just struggling to find a switch that can handle 40 amps since that's what the fan seems to be.

[TomsFocus]

12 minutes ago, bockercharlie said:

I've looked into this for a bit and it seems fairly do-able. Just struggling to find a switch that can handle 40 amps since that's what the fan seems to be.

Much easier to use a relay.  Then you just need some skinny wires an a basic switch into the cabin.

[bockercharlie]

49 minutes ago, TomsFocus said:

Much easier to use a relay.  Then you just need some skinny wires an a basic switch into the cabin.

Glad you commented Tom because I was just about to update you. Sorry for the excess detail but I am a rookie. Am hoping you can give me another push in the right direction. 
 

I did as you suggested and bridged the pressure switch from the air con underneath the left headlight. With engine running, fan comes on when air con button is pressed in cabin and only stops when engine is turned off. 

[TomsFocus]

3 minutes ago, bockercharlie said:

Glad you commented Tom because I was just about to update you. Sorry for the excess detail but I am a rookie. Am hoping you can give me another push in the right direction. 
 

I did as you suggested and bridged the pressure switch from the air con underneath the left headlight. With engine running, fan comes on when air con button is pressed in cabin and only stops when engine is turned off. 

As the fan works with the AC (albeit fooled into thinking the AC is working) then that suggests the wiring from the PCM is good.  In this case, I really would recommend getting Forscan on it to see if there are any fan related fault codes that could help us pinpoint the problem.  You could wire in an extra switch as Isetta suggests, (I've also done the same on a mates car...would annoy me on my own lol!) but I've often found bodges take longer and cost more than just making the correct repair in the first place.