Originally Posted by Brian Carlton

The chances of the water pump as the culprit are slim. If you must waste your time with a removal and replacement, you'll definitely need a 10mm box wrench with a nose rounded off in a grinder. Otherwise you'll use a 10mm open end wrench to remove the four screws holding the fan and you'll quickly round the fasteners. It's a horrible design that won't allow a standard socket or a box wrench.

So, consider sacrificing a cheap box wrench and rounding the nose on a grinding wheel before doing the job. Otherwise, you risk being in a world of hurt if you round off those fasteners.