Morning all

 

First post, be kind. I have just acquired a Mk 6 Fiesta Style Climate, 1.25 petrol, 93k miles. Loving it so far. One small issue - the cooling fan runs constantly, even from a cold start. From the Haynes manual, I believe the fan is thermostatically controlled and should only come on when the engine starts to overheat.

My guess is that the temperature sender in the cylinder head just below the coil is faulty, and I intend to replace that first. Would that be an obvious place to start, or is there a more likely fault somewhere else? No experience of small Ford petrol engines.

Any advice, suggestions, warnings or observations very welcome. Thanks for reading.

   Had    a     B max same thing happened. asnwer lay in the fuse box.

Ah, OK, never thought of that. What was the issue?

Anyone any thoughts?

I had the same problem but my fan continued to run when the ignition was switched off and the cause of that problem was a stuck relay. As a quick fix I used to tap it with a spanner until I got around to replacing it but if yours only runs when the engine is running then it is getting a false signal either from the temp sensor or a short in the wire coming from it.

not likely, but possible, that it has been fixed to run all of the time as the car overheats and having the fan running all of the time reduces the chances of it overheating in one journey.

Have you got the air conditioning switched on permanently?

Leaving the vent dial switched to 'windscreen' will automatically trigger the AC which makes the fun run constantly.

16 hours ago, billyboy said:

I had the same problem but my fan continued to run when the ignition was switched off and the cause of that problem was a stuck relay. As a quick fix I used to tap it with a spanner until I got around to replacing it but if yours only runs when the engine is running then it is getting a false signal either from the temp sensor or a short in the wire coming from it.

No, it's only when the engine is running.  There's no sign of any damage to wiring (all looks v good) so I am looking at the temp sensor as the obvious culprit at the moment.

10 hours ago, isetta said:

not likely, but possible, that it has been fixed to run all of the time as the car overheats and having the fan running all of the time reduces the chances of it overheating in one journey.

This did occur to me, in fact.  I've been watching the temp gauge closely and it gets to just below half then never moves, however long the journey or the outside temp. My guess is that an overheating engine would show some variation in temperature, even with the fan running.  No sign of wiring bodges, so I am hoping you're wrong!

10 hours ago, TomsFocus said:

Have you got the air conditioning switched on permanently?

Leaving the vent dial switched to 'windscreen' will automatically trigger the AC which makes the fun run constantly.

Yes, I have. I tend to leave aircon (when I have it) switched on full-time. I had a Mondeo for 7 years where the aircon was never turned off, and it didn't make the cooling fan run. Are you saying that having the aircon on will trigger the cooling fan to run constantly? Seems bizarre, but I will switch the aircon off and see if it makes a difference.  Thanks for the info - a new one on me. (Edit: just tried it out. Aircon on or off makes no difference. Thanks for the suggestion anyway. Hadn't thought of that.)

Thanks for the input, guys.  Will report back. I have a coolant temp sensor on order and I intend to fit that next week.  Cheers.

Edited July 21, 20196 yr by Another Richard
Update

Yes, the air con on will make the cooling fan run constantly, that's how it cools the AC gas in the condenser to operate.  It would have done the same on the Mondeo as well, there was a fault with either the AC or the fan if it didn't.

I have to say that doesn't match my experience. No car I have ever owned with aircon has run the fan constantly. The Mondeo was owned from 12 months to 8 years/80k miles and didn't do it. The only time the cooling fan kicked in was on long fast runs in hot weather, exactly as you would expect. I don't believe it was faulty all that time.

I have checked again on the Fiesta. From cold, the fan runs as soon as the engine starts. Switching the aircon on and off makes no difference to the fan, although you can hear the compressor switching in and out and the engine revs compensating.

I'm going with a faulty sensor for the moment.

Damn, waited a week and they sent the wrong sensor. Try again ...

OK, just a final update as I think it is now sorted. I had the HT leads off and the CTS disconnected before I realised I had the wrong part. All went back together to wait for the correct part. (For anyone else doing this, there are two types of CTS, one clip-in and one screw-in, and they are not interchangeable. However, you can see which type you have without removing it.) I started using the car again without really thinking about it, and then a few days later I was walking back to it with the engine running and realised the fan wasn't going. Sure enough, the fan does not now run with the engine running and the AC on. However, I ran it on the drive this morning after a trip out, and after 15 minutes or so the fan came on. Temperature of the top hose when this happened was 92-93 degrees, whereas at the start of the test it was 73. The fan ran for a short while and cut out again.

As far as I can see, that's exactly as it should be, so I am calling it cured. The only thing I disturbed was the multipin connector for the CTS (pulled off and pushed firmly back on again) so my guess is that there was a dodgy connection giving false temp readings to the ECU.

Interestingly, without the fan running constantly, the mpg seems to have improved from an average of 37.6 mpg to 41.1. The new figure is only over one tankful, so not a reliable result, but interesting all the same.

Thanks to everyone who commented for thoughts and ideas.

Just wanted to say thank you for posting the final update with the solution in your case. You have just helped me fix the same issue that I'm sure would have taken me ages without your information. Much appreciated.