My car overheats for no apparent reason. Thermostat ok, fluid ok, hoses ok... any ideas?

either blockage in the hose so fluid is not getting through or check your fan & pump.

Also check your transmission fluid level.

If you are low, that can cause you to over heat

Check the oil for radiator coolant. to check this all you need to do is pull out the oil dipstick and look for a "milky" film. Kind of looks like Bailey's Irish Cream. That will tell if you have a bad head gasket. There is another way to tell if it is, what you call a radiator check valve, the thermostat. When the car is cool remove the radiator cap, grab the top radiator hose leading to the thermostat housing, and gently squeeze the top radiator hose. If you see air bubbles in the radiator, the thermostat needs to be changed. I am a certified mechanic and have been for 20 yrs.

You could possibly have an air pocket in the system causing an over-pressure condition. Or a more severe cause is a head gasket, check for water(coolant) in the oil or oil in the coolant, that would be the best indicator. This could also be a cracked head, they have the same symptoms. Does this car have an aluminum head? If so do not drive it hot, it will warp the head, which is a major job. Open the system when cold, start the car, and idle it untill warm and watch for coolant flow. The water pump may be to blame or belt driving it. Good luck!

Depends on the car, I assume its over heating at idle or slow speeds, check the fan connections, and that they are coming on, if it is a clutch fan, is the clutch kicking in and pulling the fan? Next option would be a little wild, but the fuel mixture, if your running really lean, that would make it hot!

Check the radiator make sure air can get through the vents, might have to wash it,check to see if you have the correct amount of anti freeze/coolant with water ratio. check the radiator cap and water pump the impeller might be spinning on the shaft.

Have you check the radiator valve?

Its a little expanding valve that lets through water, when hot.

It might be stuck open/closed there only acouple of quid and you can test them by getting a washing bowl filled with hot water then dunk the valve if you see bubbles then you know its working

Have you checked your car for a diagnostic code yet? Try turning your key to the "on" position then to the "off" position three times, and see if anything comes up.

Water pump may be going out. Air filter ok?

I would change out the thermostat. It doesn't cost but a few dollars and you can never tell what's going on with that thing. LOL

Possibly a bad water pump.