Rover 75 fault finding

This is normal. If the coolant is warm, the cooling fan continues to run until it's brought down to an acceptable temperature.

The thermostat has a differential built into the temperature sensing operation. The differential is normally a degree or more. If the stat shuts down at 72 degrees it should not start the unit again until the temperature in the room reaches 73. If the AC runs and cools properly until it shuts down, I would check the thermostat. The AC can not restart immediately after it shuts off because the pressures in the system are too high at the compressor. It takes a few minutes for the pressures equalize allowing the compressor to start. If the stat tells the unit to start under high pressure, the compressor will shut down on overload. It will start and run after the pressure falls enough for the compressor motor to run.

Engine temperature sensor faulty, not supplying correct quantity of fuel to a cooler engine, wrong cold start supply mixture.

{: ) The engine control module is programmed to protect the engine by disabling the starting system whenever it detects that the engine temperature is beyond safe limits. Depending on how fast the engine cools, it will resume normal starting after cooling down for a while.
A diagnostic scan tool readout can give you a quick idea about the possible causes of your engine overheating. For the meantime, as soon as you can start the vehicle after cooling down, drive the vehicle and try to turn off or minimize the loads , and avoid traffic sitting as possible, just enough time to reach home or a nearby service shop.
There are several things that need to be checked:
The coolant level and quality, and check for signs of coolant leaks.
The cooling fans,are they operating as designed? Check for fan blades damage or cracks.
The water pump could be faulty. Check also the engine belt.
The engine oil.
If the engine temperature sensor is faulty, it can also bring inaccurate signals and may affect operation of the cooling fans.
Check fuses and relays that power the cooling fans.

You probably need to bleed the cooling system properly.

Open the cooling system bleeder screws.

Slowly fill the cooling system with a 50/50 coolant mixture until coolant runs freely out of bleeder screws.
Close the cooling system bleeder screws
Install the coolant pressure cap
Start the engine.
Run the engine at 2,000 - 2,500 RPM until the engine reaches normal operating temperature. (midway on gauge)
Allow the engine to idle for 3 minutes.
Shut the engine off.
Allow the engine to completely cool.
Top off the coolant as necessary.
Run engine again at 2000 - 2500 RPM until the engine reaches normal operating temperature.
Allow engine to idle until cooling fans come on. It should come on with the gauge about 3/4 of the way to red. - if it gets to where is touches the red, shut down immediately.
When the fan comes on, put your hand behind the fan and observe the temperature of the air coming from the fan. It should feel hot. If it is blowing cold air, the coolant is not circulating through the radiator like it should. This could be caused by lots of things including an improper/defective thermostat, corroded water pump impeller, or a blown head gasket.

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.

This is perfectly natural for the fan to continue running when the motor is turned off. I have seen them run for up to 15 minutes depending on how hot the day and the engine are. If it is not cutting off at all then you may have a problem in your heat sensor.

The cooling fan is required to operate when the engine temperature rises above the maximum operating temperature threshold.
After the car is started, it will usually take some time for this temperature to be reached.
Ensure fan runs when fan control temperature sensor switch demands.

replace the crankshaft position sensor.

Hi it is common on range rovers that the flywheel flex plate cracks or brakes up, this in turn damages the crank sensor causing the engine to stop. I have had more than one car with this same fault.
Remove and inspect crank sensor for damage10 mins job just above the sump on left side of car from underneath.
Thanks rob