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Old 12-30-2009, 02:36 AM   #73
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Join Date: Jan 2006
Location: Cyprus
Posts: 6,564
My Ride: ESS TS2 320ci
It's not a plastic impeller but rather a composite material. Unfortunately there are 3 parts that can go wrong in the BMW and other OE water pumps: impeller, bearing and seal. The Graf one with the metal impeller has 1 less thing to break although I've read a couple of posts where the metal impeller went into pieces when the spot welds broke. In that case, better to have composite material floating in the cooling system rather than metal bits. The stewart pump addresses all 3 issues with upgraded seal, bearing and of course impeller and as a plus you get the lifetime warranty & the claims of better flow and higher efficiency. If it's a remanufactured unit it probably uses the OEM housing with a new bearing, seal & impeller.
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