Bmw e34 518 with m40 engine, problem is the temp gage rises very quickly and

[skunk9992000]

the heater doesn't come on? ok so I cant work out was this is, the engine heats up quickly and the temp gage rises very sharply, and beyond halfway and near red if i let it and also the heater doesnt get warm at all, I have today changed the thermostat to see if it was this, which it isnt because the stat is now working, as the top hose it hot after a few minutes, Is it the waterpump?, please help, thanks

 

[Ange]

it could be the waterpump or it could be the miniature radiator under the dashboard which is a heating element which is connected in line with the heater fan. it could be blocked which on some cars is a pig of a job.
check to see if you can hear the waterpump bearings. if its really noisy then you know this is the problem