cooling problem

Would help if you told us which engine you have. Anyways, on all Foci the cooling fans is controlled by the ECU, which grounds one or both coils in a relay in the engine fuse box. This starts the fans at low speed, and if the ECU sees the temp rising further (measures it through a single sensor- the CHT or CTS) then it will pull in the other contact in the relay and switch the fans to full speed.

With the a/c engaged, the ECU grounds the slow speed position to run the fans all the time, unless it receives a signal from the thermostat in the air con evaporator saying the evap is cold enough (4 deg C) in which case it releases the air con compressor clutch, and 10 seconds later switches the fans off.

When the thermostat calls for more cooling, the clutch pulls in, and 3 seconds later the fans start again at slow speed.

So, if your temp gauge is rising past 12 o'clock and the fans arent running, then I suggest firstly you check the fan control relay and the 2 fuses in the engine fuse box.

I'd then put the dash in DTC mode and see wot temp the ECU actually thinks the engine is running at- your CHT / CTS may have gone out of tolerance- and sending a signal back saying the engine is cooler than it is. However in this case I would expect the dash gauge not to reach full temperature.

Tim..

Tim thanks for the info. The engine in my focus is the zetec. I checked the fuses but dont know how to check the relays if i can. When the engine idles for a long period of time it the temp gauge goes in the red and i have to shut it down , but if i am running the a/c the fans work and there is no problems with overheating. is there an temp sensor for the computer that i should be looking at ? thanks in advance Edd

engine size 2.0 zetec

The temp sensor is fine- this is cos your gauge is working fine- the gauge gets its signal from the ECU, which gets its signal from the one and only CTS (under the alternator at the back) Your problem would seem to lie either with one of the fan fuses, or the primary fan relay. I've buttered up on the wiring diagrams, and there are 3 fan relays on a/c cars, one for the a/c and

2 for fan actuation when the a/c isnt on, all of which the ecu controls. You must have a problem with one of these.

If your not reasonably conversant with vehicle electrical systems, then I would suggest you get a dealer to check and rectify the problem.

That said the Zetec E ECU is very cunning and can avoid an overheat situation for whatever reason by at first reducing engine power (wont rev over 3000rpm) and then cycling the engine onto 2 cylinders at a time (to allow the other pair to cool off) and finally it will shut the engine off alltogether. Obviously the dash will be lit up like a christmas tree during all of this, but you can at least drive the car a short distance to a place where it is safe to stop. The handbook details all of this.

Tim..

Tim

I have an extremely similar problem. I am very observant though and have done a few things and noticed some differences. The fan running while the ac is on is definltely right. I have noticed, however, that if it starts to overheat, and gets to about the 1:30 position, if i free rev the motor a few times to 3000 rpms or so, i heara the fans click on and the car cools down. as long as i watch the temp gauge and tap the throttle when it starts to overheat the fans come on and cool it down. The other symptoms are exact. Do you think this could be a faulty relay also?? How would i determine which relay is bad? thanks in advance.

Brian

Tim

also, i have a 2001 zx3 with the 2.0 liter zetec. it just seems odd that the fan comes on with higher engine rpms.......

thanks

brian