Ford 3.0L V6 "Vulcan" Water Pump Failure

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This is a water pump, removed from a 1997 Mercury Sable with a 3.0L "Vulcan" V6. (pushrod engine) The car had 150,000 miles on it at the time the pump was replaced. It's unknown whether this is the original water pump. The car had 84,000 miles when the current owner purchased it and the pump has not been replaced since then. The car suffered a thermostat failure two weeks before the water pump problem was discovered. The thermostat was replaced and the cooling system flushed to remove brown coolant. Afterwards it was noted that the heater wasn't producing heat. Other than the heat problem, the engine ran normally and the temperature gauge indicated a normal 1/3 deflection. You can only begin to see the problem from this angle:
Here you start to see the extent of the problem. The impellor damage was caused entirely by internal corrosion. The bearing and seal on the water pump did not fail and, amazingly, the engine did not overheat with this pump.
http://blizzard.zmm.com/waterpump/

6/5/2006

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How in the world did the engine not blow up? It was driven several hundred miles after the thermostat replacement and who knows how long before that with the water pump in this condition. The pump couldn't have been doing much more than lightly stirring the coolant:

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Here's the replacement, for comparison:
Ford 3.0L V6 "Vulcan" Water Pump Failure Apparently this sort of thing is common for this model: Ford TSB 01-11-6 (477KB PDF) COOLING SYSTEM3.0L VULCAN ENGINE ONLY VARIOUS COOLANT RELATED SYMPTOMS CONTAMINATED OR DISCOLORED COOLANT

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