Water Pump Tech

OE Water Pump Changes

The water pump on the left is a '99 Cobra water pump (PN: YW7Z-8501-BA) and on the right is a '96-'98 water pump (PN: YW7Z-8501-AA). The front end dimensions (e.g., those that effect water pump pulley position and mounting are identical between the two pumps.

However, there are two substantial differences on the impeller side of the pump. The first difference,which is clearly apparent, is the ring mounted on the edges of the impeller on the '99 water pump. The second difference is that the overall diameter of the '99 impeller is 2.15" and the overall diameter of the '96-'98 impeller is 2.58".

The volute (i.e. portion of the block that mates with the impeller) is identical on 96-98 blocks and the 2002 Explorer block used in this big bore engine. Perhaps, Ford found that making the impeller smaller so that the water on the high pressure side of the impellor dumps directly into the water outlet passage rather than having to flow over the inner portion of the volute and then into the outlet passage.

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