Water Pumps - The good, bad and ugly

[3gunF1guy]

I replaced my water pump 2 years ago and it has been leaking a little water ever since. Then my cps went out and I thought while I'm in there i'll replace the water pump again. Let me start by saying that the first water pump I put in 2 yrs ago I purchased from one of those BMW discount places and it was about $80.00. The new one I got was from the BMW dealer and it was $90.00. When I pulled out the "discount" water pump and compared it to the new BMW part I was suprised to see the quality diference.
http://img292.imageshack.us/img292/9782/1003906waterpumpdk0.jpg
If you look at the impellers you will see a BIG difference. The discount impeller looks like a 6 year old made it in the sand and then cast it. The BMW part looks good.

Here is a close up.
http://img337.imageshack.us/img337/7083/1003906waterpumpimpelleki8.jpg

I do not know how this thing pumps water smoothly, It's all rough and mis-shappen. I wonder what the bearings look like if the impeller looks this bad. And no I do not work for a dealer. I had to pay retail for the new BMW part.

But I thought the rest of you would like to see this.

Scott

[Washburn]

As ugly as that cast impeller looks, I would not doubt it may pump with more efficiency. Smooth, pretty surfaces don't mean better pumping, in fact rough surface might be better. I would be more concerned about the bearing and seals and I'd rather have the metal impeller than the plastic one since the reason they fail is because they are plastic.

EDIT: whats up with this forum? I can barely follow most threads. This note just got stuck in a weird place. Not to be a whiner, but is someone on top of this problem?

[ProZak]

BMW impeller still looks like plastic. Not for me, thanks. Graf metal FTW.

[Ross]

As pretty as the BMW pump may be they still suck and fail with alarming regularity.

[3gunF1guy]

The BMW impeller is metal NOT plastic. It is so well cast it has that plastic look to it. I do know that turbulance from not having a smooth impellers does not make it bump better.

Scott

[535Nick]

I thought all BMW water pump impellers were plastic, one of the ways they shave weight and make the engine more efficient?

Hence why it's a maintenance item. The price we pay for a high performance engine.