Hi! thanks to this forum and all contributors in "how to oem zetec with pats..." thread, I have managed the engine to work . ( )

Now about the cooling. At first I wanted to use radiator-mounted switch that switches the radiator fan ON / OFF .

Simple, should work, had a spare switch that fits my radiator (polo ) but this is probably to high temperature range switch. And as it sits in radiator, then engine could have 110C deg, and radiator lets say 70 . Not precise. Better if this sensor was mounted in the hose close to thermostat, so it gets water temp readig as is goes from engine directly. Probably by fitting few different switches I would evenmtualy achieve proper fan start temperature, but a meesy job - coolant flowing around, bleeding etc etc all many times, buing few switches etc. Thought to use what is in ecu (in metioned thread @snowy2 attached a diagram with fan relay, but not metioned in the end if this works , and last online on forum was in 2020... have send him u2u but maybe others there have some ideas ?

So, thought to use and ECU which has two pins for switching radiator fan (speed I and speed II ) . Should switch ground according to diagrams.

Today have tested getting engine temperature up, and pins stays close up to 103-104 C deg (read from OBD plug ). Was affraid to wait more and switched fan directly with wires at that temperature (which brings temp down nicely ).

Does some of You know at what temperature should ecu switch the fan (ecu is from focus mk1) ? thought it will be around 100deg.

Or should I just be more patient and wait for the water temperature on engine reading up to 110 deg ?


or does the ecu needs some more inputs? from the pin-list I read that ecu gets info from sensor "cylinder temperature sensor". It is not connected to thermostat housing. Not sure if this is sufficient for ecu to calculate and switch on off radiator?



cheers!
Andrzej

Is the cht sensor installed and wired up? (it should be installed next to the inlet manifold in a blind hole m12 thread x ~40mm deep, has ~100mm lead and plug on the outside)
The fan operates according to that on a focus, the temperatures readings from that sensor will appear higher than coolant temperatures, iirc the cht sensor will need to get to 120°c for the fan to operate at the lower speed, this is equivalent to approx 100°c in the coolant system.

The focus ecu also has overheat protection, which will restrict the max rpm to 3000 and run the engine on 2 cylinders to assist cooling while an overheat is detected, if the cht sensor fails this can be triggered at incorrect temperatures.

If you want further detail, have a look through the pages at this link:
https://workshop-manuals.com/ford/focus_1999_08.1998-12.2004/mechanical_repairs/3_powertrain/303_engine/303-03_engine_cooling/description_and_operatio n/engine_cooling/


If you're using a standard 40a relay, you need +30 to permanent live from fan fuse 40a, +86 to ignition live, +85 to ecu low speed terminal, and +87 to the positive of the cooling fan.
You can add a second relay for the high speed terminal output, but you will need a ballast resistor to use 2 speeds which needs to also be cooled by the fan while it is operating.

Dave

Thsnk You for detailed information! Was not aware about this overheat ECU feature.

As for the sensor it is the same as cylinder head temperature sensor ? If so then yes i have it. Engine is taken as is from Focus. I assume my temperature readings on smartphone via obd bluetooth plug are from this sensor. But dont know if those readings are corrected ? So if sensor sees 120deg it shows via OBD 120 or already corrected 100deg?
I have noticed that readings front OBD are quite equal to those front dashboard gauge. ( Sensor for dash gauge is on thermostat housing).
So will make wiring as in Your description and try to wait for higher temp.
Also will add a switch for manualy operate fan.