Water Pump

[Aitch]

My MR2 has been sat in my garage for a while due to an earth problem, which involved it turning over and over but never starting. I have been round all the earth points, cleaned them all up and eventually a month or so ago got it started. Which was great, but it spat its alternator belt as the alternator had seized.

Last weekend I had help to change the alternator, fitted a new battery, and then found the water pump was also very stiff and the belt slipped over it, threatening to ruin another one. So I ordered up a water pump and today we went to fit it. We got the belt off and found that the water pump would move freely by hand. So we fitted the belt back on and when turning over the belt moves the pump pulley. But as soon as the engine is running, it stops and the belt slips over it again.

Any ideas what could cause this?

[PW@Woodsport]

The pump bearing is knackered.

[Aitch]

But why will that make it turn when the engine is turning over to start, but not when the engine is running?

[PW@Woodsport]

The engine cranks at 200rpm but runs at 2000rpm when cold, dropping to 900 rpm when hot, i'd guess that 2000rpm is too much for knackered bearing and it locks up.