Fan goes full speed when cold engine idles

[Neviiim]

Fan goes crazy straight after I start the engine. From the moment engine starts running it takes 3-5s for fan to spin slower speed and second later it goes full speed.

Some notes:
Fan behaves normal when puma moves but when it just idles the fan kicks in again almost right after I stop.

Engine has to be stone cold (it's 2°C outside..) for this to occur.

There is always proper amount of coolant.

The fan does this every single time.

 

[John Woodward]

I had a similar problem, fan came on full speed, temp gauge went to no reading, start driving and would idle at about 3000 RPM, after about 2 miles everything was normal. Checked with OBD2 scanner, P0118 temperature sensor, before replacing I checked voltage to sender (4.8v) and resistance of the sender, which was open circuit (should have been around 3000 ohms) replaced sensor and its been fine. I think once the engine warmed up the sensor was no longer open circuit.
Not sure if this may be of help.

 

[DOH]

This is likely to be the coolant temperature sensor, or corroded connection where it plugs in or not making full connection .
To assist you a new sensor has the following resistance values . It can be tested hot off the car in a bowl of almost boiling water.

Ford Puma Coolant Temp sensor resistance values
Cold 30 .2 k ohms
Hot 5.4-5.6 k ohms

 

[John Woodward]

Faults such as this can be found with a cheap OBD2 scanner, mine was £15 from Aldi. I also have Forscan which is obviously far more comprehensive and confirmed P0118, which was the engine coolant temperature sensor, which on my late 1.7 is just below the coil pack. Despite what the Haynes Fiesta Mk 4 manual says, there is no need to drain the coolant, only a small amount comes out.

 

[caprixpack]

I replaced my CTS as I the fan was coming on at random times for no reason, I took the opportunity to replace hoses while I was there as one was leaking due to the aluminium housing growing and the other wasn't far off.