The small auxiliary water pump is on the drivers side, close to the radiator. All plastic, so they crack. The heater valves are on the drivers side firewall near the strut tower. Also have plastic parts.

If you really can't find it, get a uv dye kit and put some dye in the coolant.

A word of caution, it took many (like 10) fill, warm up, drain, repeat cycles to get the dye out when I was done, so I would suggest using 1/10 bottle of dye to start and not the whole thing. I did use straight deionized water for this flush and then filled with proper coolant at the end.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles