Hello gentleman hope you all are having a good day. I have a unique one for you guys to wrap your heads around. I have a 2003 Land Rover Discovery II with only 48k on her. Yesterday it was cold out here in Michigan so I decided to start the Rover and let it warm up while my wife got ready to go out. Aprox 10 mins after we got into the truck to find the temperature red light on and the temp gauge was just below the red. I turned the truck off for two min started it up again drove it a hour with no problems and the temperature gauge was right were it was supposed to be. Today the next morning I went and started it up same thing happened went out there ten min later and temp gauge was just below the red. I turned the truck off check the coolant tank there was very little in it. I took of the cap and it filled all the way up. No idea myself I do not see any leaks anywhere and I can hear the electric fan running just fine. Any advice would help. Thank you very much.

 

The coolant leak should be the most troublesome issue that you need to address.

But, If the car was not loosing coolant, I would say that your fan clutch has died. The Fan clutch moderates how fast the mechanical fan connected to your motor spins. As the motor heats up the resistance on the clutch should increase, speeding the fan up.

When the car is warm/hot. Turn it off and spin the fan under the shroud. It should not make a full revolution(Or something like that). If it spins freely, you need a fan clutch.

While moving your driving is forcing enough air through the radiator, so the fan clutch is not so important.

 

FIND THE LEAK FIRST - Check all the upper radiator hoses and T Connector with bleeder valve, the lower radiator hose and all the small hoses that attach to the reservoir. Also make sure the reservoir is not cracked and make sure the reservoir cap is good. There is also two more hoses that need to be checked that connect to the firewall that go to your heater core. Usually if the heater core is bad it will leak on the front passenger floor board. It can also leak from your water pump bearing. Worst case if you can't find the leak is that it's being vaporized in the engine, meaning a damaged head gasket. But normally it's a simple leak that can be found and fixed quickly. -Good Luck

 

Check for coolant leaks first, make sure your radiator and the reserve tank are filled to the appropriate level with the correct kind of fluid.

 

you need to have you cooing system pressure tested to find the leak. the fact that your are hearing the electric fan on cool day is your first warning.
i would not continue to drive the truck until you fine the problem these engine do not take well to being over heated