Help-please

[covrover520i]

Got A 1992 520i And When Its Cold It Over Revs When First Started ,to About 2000 Then Settles Back To Normal, But When The Car Was Left Running For 15 Mins The Temp Gauge Was Over Threequarters To The Red And Only Went Back To Centre After Driving It For 5 Mins; I Have Changed Air Filter, Has Plenty Of Coolant/water ....any Ideas Whats Causing This And Is It Or Could It Be Serious Or Costly ..many Thanks For Any Help=new Member

[632 Regal]

first things first, you need to clean your icm, then bleed the engine properly. Search, there tons of info to help you here.

[BillionPa]

i would also replace the thermostat while you bleed the coolant, and if you are gonna be all up in there, check all the coolant hoses for oil damage.