AO Platinum Member
Join Date: Aug 2003
Location: London, England
Re: Water Pump or Thermostat?
If it was stuck halfway it would be overheating, or at least running hot.
When the waterpump starts to fail the impeller slips on the shaft as the revs build, then grips again when at idle.
It could be a combination of the stat stuck open (causing the low temperatures at idle) and the pump failing (causing the temperatures to rise on the move)
Changing the stat is a simple job and easily DIYable.
Changing the waterpump means a full cambelt job (so not DIY unless you are very committed).
If it is due a cambelt soon anyway then you may want to think about getting it done and changing the waterpump at the same time.
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