How do i know if a car is over heating?

Stick an infrared thermometer on the hoses.

What does 'very hot' mean.

In my book if it's not boiled up it's not overheated.

Thanks all. By very hot i mean the car gets from cold to hot in about 5 mins of driving and then it stays hot for hours after a drive.
Its not boiling up.....

Anyone got an infared thermometer i can borrow?

BMW temp gauges are very heavily damped. The needle will sit at 12 o'clock throughout a wide range of actual engine temperatures. In my experience (if the gauge is working correctly) the needle going beyond 12 o'clock would be a sign that something might not be right, but otherwise I wouldn't be worried.
Also, depending on what model BMW it is, it'll likely have a viscous fan and the electric fan will just be for air con. Certainly the case with e36s.

Depends which BMW it is. If it's an E46 they are damped, yes. M3s in both flavours are exceptions to the rule. If it's an E9x it will only have a light.

If it's the latter they do run hot, and it's normal. Why? Emissions and fuel economy is why.

obd reader and log the coolant temps. We had a fiesta a while ago that was similar. Fan switch often is set much higher than you would imagine too. Fiesta was 105 degrees but we have seen some as high as 115 before they operate.

I had a 330Ci (e46) that suffered overheating due to a previous owner removing the electric thermostat, this is in the fan controller circuit which meant that although the thermostat was always open it prevented the fans from running (slightly redundant mod I thought).

The car was ok most of the time, it got "hot", i.e. when stuck in traffic you could smell hot coolant and when shut off the engine would be hisssing and ticking as it cooled down. Temp gauge only moved off "fine" to "hot" after I was stuck in traffic in the middle of summer and the car was proper overheating (steam coming out under the bonnet and that smell.....). It only indicated "meltdown" (goes off the scale and a red light comes on) after the coolant header blew up as I was finally escaping the traffic. Good times.

On the e46's the fan controller can be overridden by pulling the fan fuse and using some spade terminals to add a remote switch inline with the fuse and then taking a permanent 12V feed from another point in the fuse box. Also there are 3 temp sensors, fan one is on bottom rad hose, there is another on the thermostat housing and one in the block somewhere.