Think your radiator clutch fan has locked itself up, I had the same problem a while back. Here's what greg told me
"Sounds like the fan clutch has locked up, that's if it's a belt driven standard fan unit.
Certainly NOT normal and will disintegrate the fan if you leave it like this.
The fan clutch is designed to slip so the fan NEVER goes above about 3000rpm. If the fan clutch seizes, then the fan will rev way over its designed limit and then they just fly to bits, usually wrecking the radiator at the same time.
You should be able to grab the fan blade with a cold engine idling and it will slip in the fan clutch. I don't suggest you try this, but that's what you can do when it's working properly.
Obvious tell tale signs from a seized fan clutch are the huge fan noise, like a jet taking off and very poor fuel economy as the fan will now be drawing lots of power.
With a hot engine, not running, the fan must be free to rotate by hand. If it's stiff, grabs or make grinding noises, there you go.
Greg."