OK I am hearing that this is a plastic versus metal impeller issue, but does anyone have any idea what type of polymer Ford's supplier uses? From a material technology standpoint the 'plastic' must be a thermosetting type rather than a thermoplastic type meaning heat cannot be used to reform/remold the material (it does not melt) and that only it's upper temperature limit will cause it to degrade and breakdown. My understanding is that it is a phenolic which means it is hard and brittle unless it has a some strengthening agent such as fibreglass etc. However from a strength comparison the 'plastic' impeller will be and order of magnitude or 2 less in strength than metal like steel. As for efficiency of pumping the 'plastic' impeller being more efficient than a metal one is purely a manufacturing issue and a dependent on cost. Metal impellers are used in all kinds of pumps and are of high efficiency. I have designed all kinds of pumping systems from small to large from 2 inch piping up to 14 inch piping and the calculations are the same and take into account the same basic parameters. The pump is chosen from ones available to do the job. It is not designed from scratch for the project. If Ford wanted to use a high efficiency metal water pump instead of plastic it could have used a cast metal or forged metal one from those that exist already. Even metal stamping processes can produce parts of the desired shape given the correct steel material used. This was a cost per unit issue for Ford given other physical parameters for the water pump. It was a trade-off. Ford made the decision based on expected lifetime and overall manufacturing costs for the car. They made a mistake. It is that simple. Replacement ones that are of metal impeller design will be appropriate for the engine if selected for quality rather than cost. Choose carefully.
