I am needing to replace the water pump in my 07 base Cayman and there are numerous choices. The factory is composite, some aftermarket are "metal" some are brass. Since the factory item seems to be a given to wear out in 40,000, which should I choose?
Lots of opinions on this. "They" say a failure of a plastic impeller will let chunks into the water passages and get lodged in places causing hot spots. "They" also say a metal impeller can chew up and destroy the block if the bearing gets loose. Most seem to go with plastic. I went with metal. I think a bad bearing will cause the seal to fail and start leaking before it gets to eat up the block. At least thats what it did on my original pump. Bearing failed and it started leaking real bad before the impeller made contact with the block. I am a bit of a risk taker, for the record.
water pumps are a wear n tear item. its not just the impeller but the bearings, shaft and pulley. Not sure if there is going to be a huge distinction made by the type of impeller. In my car, the original was a non metal one and was replaced with original parts.
I went with plastic. Cleaning out broken bits seems easier than dealing with a damaged block. Mine started making noise at my office and there was some visible damage to the block in my 12 mile drive home with only a minor leak.