Just wanted to share my latest cooling system headache with everyone in case it helps someone out.
Background 3 years/30,000miles ago I installed a Graf water pump with cast metal impeller. I didn't think much of it at the time because metal impeller was supposed to = good.
Lately, I had spots of coolant slung all over the front of my engine bay. Turns out that coolant was leaking past the bearing on the Graf and hitting the pulley which sprayed it everywhere. It was also apparent that the bearing was shot because the shaft had a significant amount of play in it.
Tech From what I have read, BMW had 3 versions of the water pump. First was a plastic impeller (this caused all the original horror stories), second was a stamped/welded metal impeller (metal impeller was too heavy/costly and wore out bearings), and the latest is the composite impeller (OE manufacturer is Saleri). The cast metal impeller was never an OE option.
Results I replaced the water pump with a
Saleri unit from pelican which has a composite impeller. This is the OE BMW water pump without the OE BMW price. The Saleri weighs 0.5lb less than the Graf, which seemed to be due to the lighter impeller. Hopefully, this will help extend the bearing life.
The composite impeller also has much more uniform ports which can only help to improve the flow characteristics.
I've been watching my water temps since doing this and the engine is running a consistent 6F cooler. Also, my temp needle used to be a hair to the right of middle since I put the Graf in. Once I put the saleri unit in, back to dead center.
There are quite a few reviews and stories popping up on Pelican Parts and bimmerforums about people having issues with Graf pumps. I can only encourage you to research it yourself and make an educated decision before buying.
From left to right: OE composite, Gebu/Graf cast metal, OE stamped
Check out the terrible port sizes on the cast.
Photo borrowed from Joemamaman on bf.c (his thread is below)
Cliffs:
Graf = Bad, Heavy, poor flow, chinese bearing?
Saleri OE = Good, better bearing, good flow
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