2005 focus overheating at speeds greater than 45 mph. Does not overheat at idle. Gauge goes back to normal immediately when speed is reduced. Radiator, thermostat, coolant reservoir and sensor have been replaced. No change at all.

is cooling fan working? A failing water pup will do this problem. the impeller is stamped steel and it will erode or the the pump is bypassing water inside.

Are your "cooling fans" working? Let the engine run until it starts getting hot, the cooling fans should be running if not check the fuses and fan motors.

Throttle Learn
Description
The engine control module (ECM) learns the airflow through the throttle body to ensure the correct idle. The learned airflow values are stored within the ECM. These values are learned to adjust for production variation and will continuously learn during the life of the vehicle to compensate for reduced airflow due to coking. Anytime the throttle body airflow rate changes, for example due to cleaning or replacing, the values must be relearned.
A vehicle that had a heavily coked throttle body that has been cleaned or replaced may take several drive cycles to learn out the coking. To accelerate the process, the scan tool has the ability to reset all learned values back to zero. A new ECM will also have values set to zero.
The idle may be unstable or a DTC may set if the learned values do not match the actual airflow. Without Scan Tool - Learn Procedure
• DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0122, P0123, P0128, P0171, P0172, P0174, P0175, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0222, P0223, P0300, P0351, P0352, P0353, P0496, P0601, P0604, P0606, P060D, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, or P2176 are not set.
• The engine speed is between 450-4,000 RPM.
• The manifold absolute pressure (MAP) is greater than 5 kPa.
• The mass air flow (MAF) is greater than 2 g/s.
• The ignition 1 voltage is greater than 10 volts. Without Scan Tool - Learn Procedure
Important: Do NOT perform this procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
Start and idle the engine in PARK for 3 minutes.

The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
Ignition OFF for 60 seconds.
Start and idle the engine in PARK for 3 minutes.
After the 3 minute run time the engine should be idling normal.
Important: During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.
? If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.
After the drive cycle, the engine should be idling normally.
? If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.
Once the engine speed has returned to normal, clear DTCs and return to the diagnostic that referred you here.

check grill and radiator fins are not plugged and fan is not damaged and is working.
sounds like a thermostat or water pump issue.

overheats at idle only are typically the fan system. Cars use the fan to pull air across the radiator for cooling. Any speed over 10 mph there is more than enough natural wind to do this without a fan. If the problem immediately goes away when you start moving, it is probably a malfunction or issue with the fan. I have on more than 1 occaision had a customer tell me they had the fan replaced and car was still overheating, and it ended up thje fan was spinning backwards or not turning on because of a fuse or relay issue.

If it doesnt cool down fully once speed is above 20mph for more than 30 seconds, there may be other issues like plugged radiator or weak water pump impellars. water pump is a fan that moves water instead of the air. if the blades wear, they still kinda work, but at idle they work poorly because the broken blades only move a little air at low speed, rev the engine up, they spin faster and work better. If the fan is functioning OK (Turns on and off by itself) and car still runs warmer at idle than at rev, water pump may be worth investigation.

Does the radiator fan come on before it overheats?
And is it boiling over, or just showing hot on the gauge ?
Is the cooling system full of coolant and no air pockets ?
How do you know the thermostat is ok ?

100 degrees is the normal operating temperature for the motor. If it goes higher than that, the thermostate needs to be replaced. The temperature will be higher on the highway because the engine is producing more heat energy due to the higher load on the motor. Diesels idle cooler and the engine will cool down at idle or lower speeds. That is why it is best not to idle your car for long periods of time because this will cause deposits in the engine and glaze the cylinders. The engine is working normal from what you described and there is no reason to worry. I hope this helped.

At idling speed an engine does build up a lot of heat and the cooling fan will kick in. In slow moving traffic or traffic jams the temperature gauge can touch the red - particularly on hot days. The reason it cools down when you start moving is because of the air flow through the radiator.

Presumably there are no leaks from the cooling system otherwise you would have mentioned it. In normal circumstances the fan will not be running as you are driving at speed, as the air-flow through the radiator is sufficient to cool things. The fan only kicks in to get rid of excess heat - and this usually occurs at idling speed or after you have parked the car.

If the fan is running all the time as you drive, this points to either a fault in the fan switch, or the car is running too hot. presumably in normal driving the fan isn't running and the temperature gauge reads normal?

It is common - in stationary traffic many cars overheat (particularly big engined models) try to stall and 'cut out'. Restarting can be difficult until the engine cools down.

Is your car overheating in normal driving conditions or just at idle speed? Overheating in normal driving conditions can be caused by things like a failing water pump, blocked radiator, collapsed hose, faulty thermostat or, in the worst case scenario, cylinder head problems.

Overheating at idling speed is 'common'. Check your coolant level. If your car isn't using/losing coolant then there probably is no major problem. You can flush out the cooling system and refill with new coolant - and also check your radiator. Are the cooling fins crumbling with age? Or maybe they're partly clogged with insects and debris from the road? A blast with a hosepipe wil sort that out ..

The question is how much does your car overheat in normal driving? If it doesn't .. it appears as though you have nothing to worry about as such. Most cars have 2 speed fans... the 2nd faster stage kicks in at some point dependant on engine temperature. Perfectly normal.

sound like the trans is gettin hot, i would have a trans cooler installed

If you haven't flushed your radiator, i would recommend this asap. i would also inspect the water pump and thermostat as well. replace both components if found to be faulty.

Make sure the cooling fan is operational. it should cycle on and off if the air condition is activate.