Sunday, November 8, 2009

BWM Water Pump Replacement

I guess it was about 6 weeks ago now, we were driving home from dinner when the car starting making these awful noises.  We limped it home and opened up the hood to see the fan stuck up under the fan shroud, where it obviously was never meant to go.

After working myself up to the task for five weeks, I finally went and opened the hood up again to see what I could find.  I initially intended to pull the shroud out (since it was warped from the collision) and see if it would work without any major repairs.  To get said shroud removed requires taking the fan out too, since the tolerances are too tight to remove one without the other.

Removing the fan was only minorly painful, it nominally requires a 32mm open end wrench and a special tool for holding the fan pulley, but I was able to make it work using a large crescent wrench and a screwdriver.  Once I had some leverage on the fan, I noticed the shaft it mounts on was wiggly (which it definitely shouldn't be), which got me reading and I found out the fan mounts to the water pump.  I hate water pumps.  They suck and should be cause enough to switch over to electric engines.

The water pump in my BMW is a known suck-fest.  It is a recommended maintenance replace item every 60,000 miles, so it wasn't really surprising that it had failed.  To replace the part itself is pretty easy, it's almost like the engineers knew it was going to have to come out regularly so they made it easy to get to.

I have the 2.8L BMW Z3 coupe (engine M52 TU)
  1. Remove fan and cowling - 32 mm wrench and either a special tool or a large screwdriver to keep the pulley in place.  The fan is threaded onto the shaft CCW, so righty loosey.  Pop the two rivets on the cowling (one in each top corner).
  2. Get the belts off - for each belt, there is a hydraulic tensioner which keeps everything tight.  Pop the covers off these with a small, flathead screwdriver.  A T50 torq bit in a nice long socket wrench gives enough leverage to push the hydraulic tensioners down, letting you slip the belt off the pulleys.  The more forward belt runs the AC, the longer serpentine belt runs the water pump, alternator, and power steering/brakes.  You have to get both of them off, and should probably replace them while you're doing so.
  3. Remove the pulley off the water pump - 4 bolts, 10mm heads
  4. Drain the coolant system - There is a valve at the bottom of the radiator on the drivers side.  There is a valve at the bottom of the engine block, exhaust side, and cylinder 2
  5. Take the nuts off the water pump - 4 nuts, 10mm
  6. Use two M6 bolts in the threaded holes on the water pump to push it out of the engine block, try to move the bolts evenly
  7. Lube the gasket on the new water pump with clean antifreeze
  8. Reverse removal steps with the new pump
  9. Once it's all put back together, fill the coolant system and bleed the air out - turn heater to high, fan to low, and idle the engine, once the bubble stop coming out at the bleed screw, you're done.  Don't forget to check the level after the first time you drive the car.
All in all, it was a straight forward repair.  It only required buying 1 new tool (a T50 torq bit), new belts, new water pump, and anti-freeze for a total of <$200.  I would do it again instead of taking it in to a shop.

Don't forget that antifreeze is nasty bad for critters, so clean up after any spills, don't leave any AF out, and make sure not to kill your pets.  Apparently it gives them liver failure and they die a slow, horrible, painful death.

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