Avus Autosport, Inc. Blog

Cooling System Preventative Maintenace
M50, M52, M54, S50, S52 (US-spec) Six Cylinder Engines
By Mike Miller

BMW six cylinder water pumps have had premature failure problems since 1992, despite several redesigns. It it rare to see a failure before 60,000 miles, but from then-on you’re on borrowed time. And sometimes, the water pump failure leads to complete engine melt down — if the driver fails to shut down the engine immediately.

It doesn’t matter if you have the early plastic, the late plastic impeller, or metallic impeller, both fail premature only in different ways. The original design of the OEM pump had a plastic impeller, which would disintegrate and cause overheating and sometimes engine damage. The later OE design had a metallic impeller, and the bearing would seize, causing overheating and sometimes engine damage or destruction. Now we’re back to plastic impellers. Are they better? Who knows? I have had it with these water pumps.

I recommend the following preventative replacement schedule for the cooling system on this car:

Every 60,000 miles: water pump, thermostat, plastic thermostat housing if so equipped (or replace it once with the aftermarket aluminum thermostat housing)

Every 90,000 miles: radiator, expansion tank, fan and fan clutch if so equipped (for cars you’re going to keep forever, consider using the all-aluminum radiator and expansion take from www.zionsvilleautosport.com and you won’t have to do it again at 180,000)

Every 150,000 miles:  all coolant hoses

Every two years: drain and fill coolant, including draining the engine block by opening the drain plug on the right side under the exhaust manifolds, replace using fresh original BMW anti-freeze mixed 50-50 with distilled water

As for the EMP Stewart Heavy Duty Water Pump, they are too new for a verdict really as I haven’t heard of any with high mileage. I note they are marketed as a “high performance” water pump and as much is made of their supposedly improved efficiency. They look good on paper and in person, though, and I plan on installing one on my car to see how long it lasts. The performance of the original water pumps was never a problem. The problem is their lack of durability.

It actually pains me to recommend replacing the entire cooling system preventively before 100,000 miles, as above. Yet experience has shown this maintenance is cheap compared to the alternative. There is no shortage of engines destroyed in these cars by premature cooling system failres.

© 2008 Mike Miller