Early 6-cylinder E36 BMWs were built with water pumps that have plastic impellers. Over time, the impellers become brittle, crack, flake, and eventually stop spinning altogether. This is a well-known problem. BMW replaced the plastic-impeller pump with one that had a metal impeller in production at some point in 1996, for cars sold as model year 1997. These pumps were not without their own problems, though: they were prone to bearing failures. The third (and hopefully final) water pump is the one now available from BMW. Its impeller is made of a composite material.

A failing water pump may not exhibit any symptoms. This pump came off of my 1996 328is during an overhaul of the cooling system in January 2005. The car (and pump) had 83kmi at the time. First, a head-on view of the impeller. Note the cracking:

The next picture shows how parts of the impeller are flaking. The material that is missing where the surface is uneven should have been taken care of when the cooling system was flushed.

Here is the scary crack on the rear of the impeller where it meets the shaft. Like most other scary cracks on the rears of things, it doesn't leave you with a warm and fuzzy feeling. (An overheated feeling, maybe.)

Evidently, this pump was in pretty sorry shape. Driving the car with it installed, you'd never have guessed that it was a disaster waiting to happen.

Finally, this is the old plastic-impeller pump alongside its replacement, a new one with a composite impeller.

If the water pump in your E36 325i, 328i, or 323i hasn't been replaced yet, do it now. If you're not sure if it's been replaced yet, do it now. You should be able to tell what type of pump you have without removing it based on the casting's date stamp, but considering that the steel-impeller pumps initially used as replacements also had problems, it's wise to just replace the pump with the current part.

Pick a different trade.

Mark Mentovai
2004 February 17