O/T Ford Fiesta Rad Fan sensor

[Graham King]

Folks, a bit of a long shot on this one but wonder if anyone can help.

 

My son has a Ford Fiesta Zetec S 2001. We have had problems with this overheating which now appear to be sorted, it has a new water pump (replaced as part of cam belt change), new thermostat, new rad and new heater control valve (which are problematic on these). The car now runs fine with no overheating, however the rad fan is on permanently, it comes on shortly after the car reaches operating temp. Unlike any other car that I have worked on where the fan sensor has been in the actual rad itself, the Fiesta has one of these sited in the fan cowling, it doesn't actually touch the rad at all. I have also replaced this with a new one as the old one was badly cracked but it has made no difference.

 

Firstly can anyone tell me what it is, I assume it is a thermo switch of some sort but is it sensing the temperature of the air around the rad or something else. Secondly, I found out to my cost that the green surface of it gets very hot (way hotter than the rad or air around it), I assume that this is the current flowing through it but again can anyone explain?

 

I am beginning to wonder if the fan is meant to be on all the time, the car has an aircon rad directly in front (so in the direct airflow through the grill) of the coolant rad.

 

Any advice would be appreciated as this is now driving me mad and it's getting expensive. ☹️

 

Thanks.

 

Graham.

[Stationary M25 Traveller]

It says it is a resistor for the fan - thus it will get hot as it is energised. Assume it controls the speed of the cooling fan. There will be a sensor in the water path somewhere that switches the fan, or the temperature sender that is connected to the ECU does this too.

 

Have you got the Haynes manual ?

[Klunk]

The fan switch should be in the top radiator hose on the underside, halfway between the rad and the thermostat housing on the cylinder head. It may not be visible when looking from the top but it should be there.

 

Regards,

 

Giles

[Graham King]

Ian, that makes much more sense, I couldn't see how it could take the temp of the rad

 

Klunk, do you know if the fan switch is separate from the engine temp sensor or if the ECU switches the fan based on the reading from the engine temp sensor, the engine sensor was renewed as well and is in between cyl 2 & 3 on top of the head. There is a housing on the side of the head that the top hose connects to, I'll have another look around that to see if I can see a separate sensor.

 

Thanks both, excellent info as usual.

 

Graham.

[Klunk]

Graham,

 

I have just realised; this is a zetec se engine (sigma) isn't it? I was thinking it was an earlier zetec engine

 

I will be able to tell you where it is once I get home and look at my Autodata software.

 

Regards,

 

Giles

[Graham King]

Giles, it is a 1.6 Zetec (think you're right about the SE), 2001 in a Fiesta. It has aircon which I think is relevant. I have a Haynes manual for the car but it doesn't reference the resistor at all. I have found a website that appears to infer that the fan will be on continuously when the aircon is turned on. Ours is on all the time regardless of aircon operation.

 

If you can get any further info that would be excellent.

 

Thanks.

 

Graham.

[Klunk]

Graham,

 

From what I can see, the sensor you have replaced in the head controls the fan via the ECU.

 

I know it's new but it may be worth checking the resistance of the sensor at the following temperatures. The resistances should be:

 

34000ohm at 20deg

1300ohm at 85-90deg

 

It seems to be a common problem here and here. (The second one is a 1.8 focus but there is a reference to a 2001 Fiesta in the thread)

 

Do you have any fault codes?

 

Regards,

 

Giles

[Graham King]

Giles, excellent thanks, I had seen the first link but not the one on pistonheads, sounds almost identical. I don't have any fault codes (I assume I need something special to do that), I do have a multimeter so can check the resistance as it warms up, can't check the coolant temp unfortunately as the gauge doesn't have any markings other then a red zone.

 

It may take a day or so to check it but I will post back when I get the resistance readings.

 

Thanks again, really appreciate all your help.

 

Graham.

[Klunk]

Your right Graham, you need one of the many ODB II tools available to read the codes in the ECU or get it diagnosed by a garage.

 

I would have thought that 85-90deg will be the normal running temp when fully warmed up. So wherever the needle normally sits when fully warmed up (assuming the gauge is accurate! )

 

Depending on what you find out in the next couple of days, at about £60 a go at a garage, I would buy a code reader - at least you'll have it for the future.

 

Regards,

 

Giles

 

 

 

Edited by - Klunk on 3 Dec 2012 21:24:07

[Stationary M25 Traveller]

I have one those contactless laser temperature measuring things if it helps.