On the way back home from holiday in Scotland I was overtaking a coach when the TDS had a drop in power, I looked down at the gauge and saw the temp was in the red. The car had the opposite issue when I bought it and wouldn’t heat up which was solved by replacing the thermostat and viscous fan. Having been recovered home by Green Flag I set about diagnosing the issue but had ruled out the water pump as I understood that BMW had replaced all of the older plastic impeller pumps with metal impeller pumps in 1996. I was wrong and the pics below show the problem.
There’s not much documented about the TDS M51 engine so I though I’d do a quick how-to for Thermostat and Water Pump replacement. Unfortunately I was in a hurry to get the car fixed so I didn’t take many photos, but hopefully the descriptions will help.
1. Release the pressure by removing the expansion tank cap.
2. Drain the coolant using the plug at the bottom of the radiator
3. Remove the plastic bonnet slam tray (four screws & two push-pins)
4. Remove the air filter flexi-pipe and unclip the mount
5. Remove the engine “T” cover.
6. Using a screwdriver as a wedge jam the pump spindle and undo the viscous fan using the correct spanner, turning clockwise.
7. Remove the radiator shroud. Note where it clips into the radiator at the bottom and sides.
8. Make a note of how the drive belt snakes through the pulleys, then get a friend to release the pressure on the drive belt tensioner with a bit of wood and slip the belt off the water pump pulley.
9. Undo the MAF wiring from the thermostat housing and undo the three bolts. The thermostat housing should come off easily.
10. Next undo the 4 bolts that hold the water pump on. Take two of the bolts and re-insert them into the holes at 9 ‘o’ clock and 3 ‘o’ clock on the pump. Gradually tighten each screw in turn and this will pull the pump from its housing. On refitting use some silicone spray on the pump seal to ensure it slides back in smoothly. Refit the 4 bolts and tighten to the appropriate torque.
11. Now fit your new thermostat, ensuring that the small bleed valve lines up with the indentation in the housing. Refit the 3 bolts and tighten to the appropriate torque.
12. Refit the drive belt, fan shroud, viscous fan (anti-clockwise), engine and slam covers and refill the system with a 50/50 coolant/water mix. The TDS has an expansion tank and is self bleeding unlike the petrol 6-cylinder models.
13. Run up to temp and check for leaks. If all is well your new pump is good for another 100k.