Why does my car Overheat?

First is it overheating on the highway or stop and go...If the fan is the problem it should not overheat at high speed...if it overheats all the time you have a different problem...are you loosing any coolant?

Sensors do not always throw codes if they are close to normal parameters, needs to be checked with a scan tool and thermometer.

There is usually a high and a low speed fan relay, as well as a separate A/C fan relay (also high) Your High speed fan relay could be bad, or the fuse for it.

Engine idle surging usually means the coolant is boiling and there is no longer liquid in the throttlebody causing it to go to a high idle because it thinks the engine is cold. Warm coolant closes a valve lowering the idle on most Japanese makes of that year.

Also, sometimes Thermostats stick half open and do not allow enough flow. AND sometimes in neglected cooling systems Water pump Vains are eroded by electralosis causing low coolant flow as well. And a Clogged radiator can also cause this, as by the time the fans run on high it's to late.

sounds like your cooling fan isn't working at high speed the air will cool the engine but when your at low speeds there isn't enough air to do so so i would check your cooling fan that is more than likely your problem hope this helps.

I would make sure the radiator fan is working correctly.
It should come on with the ac or when the engine reaches 220 degrees.

You might need to replace fan assembly and/or thermostat. Mine was overheating only when stopped at traffic lights. Only one fan was working and would cause the car to overheat. Working great after fan swap.

when does it overheat ? wile driving at hiway speeds ? or at idle or wile driving in stop and go traffic ?

if it overheats on the hiway, supect a restricted radiator, or a blown head gasket or cracked cylinder head.

if it only over heats at idle or in stop and go traffic, supect no cooling fans.

Check the coolant temperature with the car stopped. At idle with the hood up keep the thermometer in the coolant. Confirm if the coolant is not overheating but the engine is!!

Run the A/C keeping the thermometer in the coolant and allow the fan to kick on.

If with the A/C on the engine doesn't overheat then it confirms that the low speed on the fan motor is not working. Read the description of the Taurus where the low speed is used for normal operation when temperature is required but the high speed is activated when the A/C is on. The circuit is simple.

In your case the low speed has to be activated for the A/C to go into the high speed. The fact that the high speed is working and low speed is not indicates the low speed of the fan is defective.

Other problems such as the thermostat or plugged cooling system(radiator clogged) could be the root problem!

Hope this helps?

Two things come to mind: 1) The electric fans are working intermittently, and somehow stop receiving electricity at high engine speeds. With the car stopped, in park, wait till the fans come on, and have somebody else race the engine while you observe the fans to see if they stop. 2) Happened to me once that a mechanic reversed the polarity of the fans, so they would run backwards. At idle it is no problem, the fan just pushes the air outwards, toward the bumper, but at high speed, the fan air cancelled the oncoming fresh air, and the car would overheat instantly.

check level of fluid

try the main fan. Then check strip fuse for the Aux fans. Then check A/C charge or the sensor that checks it because that turns on the low speed on the Aux fan. Then check the Engine temp sensor as that controls the high speed Aux fan control.
Also a stuck open thermostat will cause overheat.