Hi all, I’m new to the owners group. So I’ve had my 1.25 2012 mk7 fiesta for about 10 months now. Obviously there’s been the occasional age and mileage related issue however nothing too big. However, 2 days ago I was stuck in stationary traffic for about 40 minutes and my engine suddenly overheated and sent coolant our the cap. Obviously it’s not supposed to have done this so I took it to work ( I work in a HGV garage as an apprentice ) once it had cooled down to try and find the fault. I thought the most likely cause would be faulty fuse and/or relay for the fan however when I isolated the fan and tested with a power probe it spun. This is strange as there’s power from the fuse board and down to the plug but yet it still overheated? I have switched the relays around to see r1 and r2 if it was the relat at fault but it seems fine. Also, I was not able to find a correct fuse board diagram for my car but have made and educated guess r1 is for the fan from other boards I’ve seen. I’ve now driven it 15 miles to test the fan to see if It spins and it seems like my temperature won’t get passed 90 no matter the fact it’s under load and had been idling for 30 mins before hand. Whilst on this drive the ‘engine malfunction service now’ light has come on. Does anyone have any suggestions as I’ve tried every electrical option with the fan so 1) I don’t understand why it overheated and 2) why the engine malfunction light has come on.

 

 

Any help would be appreciated and obviously times are tough so paying for a diag from a Ford garage is last case.

 

Cheers in advance.

14 minutes ago, Tmetter said:

I work in a HGV garage as an apprentice

Just think of the Fiesta as a mini HGV and fault find like you would on something bigger. 🤔

Start by getting the Ford specific DTC's using FORScan (not a generic code reader).

Try unplugging the coolant temp sensor.  Then start the engine.  That should bring the fan on as a failsafe if everything is working with the fan control.

And also invest in Forscan to check the fault codes from the warning light, as above.

Does your fan have two speed control with a resistor on the bottom corner of the cowling?  (I don't think it will but worth checking in person)

On 3/12/2025 at 11:13 PM, unofix said:

Just think of the Fiesta as a mini HGV and fault find like you would on something bigger.

When I changed my wet belt I obviously had to tackle the stupidly tight crank bolt. My neighbours Dad is an HGV mechanic and so he brought some tools round - the sizes in his socket set pretty much started where mine finished off! 😂

Edit: I knew I had a photo somewhere:

(The one outside the box is mine, and a 22mm I think!)

Forscan is the way to go as suggested. Download to laptop you will need a cable from USB to Diagnostic port. OBD11.  Maybe a sensor or wireing issue as its not the fan, fuse or relay. Water ingress ? high resistance joint. 

On 3/12/2025 at 10:56 PM, Tmetter said:

However, 2 days ago I was stuck in stationary traffic for about 40 minutes and my engine suddenly overheated and sent coolant our the cap.

Are you sure it was that way round? Or, could it have been the cap ruptured / came off first thus lowering the boiling point and allowing an excessive amount of coolant to evaporate?