E36 (K reg) Temp. overheat light

Your water pump's plastic impeller has parted company with it's metal shaft. You need a new pump, I'd do the thermostat at the same time. About 25 for the pump and 6 for the thermostat from euro car parts.

Just out of interest. What does the bottom of the rad look like visually?

Me thinks you have a stuck thermostat.

I'm with John. I said the tstat was gone, earlier. But, in retrospect, the water pump is a huge suspect too. In any case, replace them both.

Thanks to John, Jeff and Leroy for your comments. Really appreciated! I think I will change both the pump and the thermostat. I wasn't planning on changing the pump but I guess whilst most of the engine is in pieces I may as well! Leroy, with regards to your question, the bottom of the rad is clean. Well, it isn't showing any signs of leaking. I have had it suggested to me by a friend that the sudden jump from normal to hot on the temperature gauge could be an indication of an air blockage in the system. This would fit in with the fact that one of the hoses (exiting the rad) felt empty (no water inside) and cold!

OK. The reason I asked was because I remember that there was a problem with the rads whereby the bottoms would bow out. I think that this was a year or two later though.

They are a pain to bleed. Have a look on google for the procedure.

Na, rubbish, the M52 can be a pain to bleed, not the M50.

I thought they had pretty much the same cooling system? I have an M52 but never had an M50.

I know the M42 is a cut down M50, and they can be a pain.