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There is a special tool but usually the strap wrench will work, you have to shock it to get it loose. With the strap wrench on use a hammer on the wrench and give it some sharp hits until it comes loose.
The nut needs to turn the same direction as the engine to come off, look at you new pump threads to be sure you are going the right way.
Also make sure you put the belt back on correctly as you can easily reverse it on the pump and it will overheat.
If your looking at the engine can you tell me which direction i should be turning the nut? Im not sure which way the engine turns, so should i turn the nut towards the battery on the right or towards my coolant and window wash resivoir on the left
Left should be loose on that one, I always double check the new pump threads to be sure since I work and al models and engine sizes.