I have an annoying overheating problem. Often, the car warms up from cold very quickly and goes straight into the red zone after approximately 5 minutes. It then stays there for the next 10/15 minutes before dropping down to normal temperature and not budging,. It doesn't do this again in the same day; despite being sat for several hours. I've done the obvious and changed the thermostat (twice). I was advised that it could be the water pump. Apparently, some have a plastic impeller that can slip on its shaft. This sounds feasible. Has anyone else had this issue? It's a big job to change, so I don't want to do it unless someone has had the same experience? Thanks.