R107 Water Pump Replacement

As an Amazon Associate I earn from qualifying purchases.

The water pump on an R107 V8 sits at the front of the engine behind the fan. It is a wear item, and a leaking or noisy pump is a common reason for overheating and coolant loss.

Failure signs

• Coolant drips from the weep hole under the pump
• Dried coolant trails down the front of the engine
• Grinding or whining from the front of the engine
• Fan wobble when you grab a blade (engine off)
• Overheating with no other obvious cause

What else to replace

• The fan clutch, if it has any wobble or leaks (fan clutch)
• The thermostat and its gasket (thermostat)
• Radiator hoses and the small bypass hoses
• Drive belts (belts)
• Coolant, using the correct type

Steps

1. Engine cold. Drain the coolant.
2. Remove the fan shroud, then the fan and fan clutch from the pump pulley.
3. Loosen and remove the belts.
4. Remove the pulley.
5. Remove the hoses and the pump bolts, noting their lengths and positions.
6. Separate the pump from the housing carefully; on many M116/M117 engines the pump bolts to a housing and only the pump itself is replaced.
7. Clean both surfaces fully.
8. Fit the new gasket, a thin film of sealant only if specified, and the pump. Tighten bolts evenly to spec.
9. Reassemble, fill and bleed the system as described in the radiator guide.

Gasket and sealant

Use the gasket supplied with a quality pump. A thick layer of silicone can break off and block passages. Clean, flat, dry surfaces matter more than sealant.

Time

Allow three to five hours for a careful first-time DIY, less for an experienced mechanic. Seized fan clutch nuts and bolts are the usual delay.

Cost

A quality pump is moderately priced. Shop labor typically adds a few hours. Doing the pump, thermostat, hoses and coolant together makes the labor go further.

Quick answers

• Can a pump leak only when cold? Yes, seals often weep cold and seal up when warm. It still needs replacing soon.
• Is a small weep normal? A trace of dried coolant at the weep hole is a warning sign; an active drip is a failure.
• Should I buy the cheapest pump? No. Choose a known brand; a cheap pump can fail quickly and the labor is the same.
• What are the signs of a failing water pump? Coolant weeping from the weep hole, a wobbling fan pulley or a grinding noise.
• Should I replace the thermostat too? It is cheap and accessible during the job, so many owners do.
• Is it a DIY job? Yes, for a careful home mechanic with the right gaskets and tools.
• Do I need to bleed the cooling system? Fill slowly, run with the heater on full and top up as air escapes.

Related reading

• Overheating causes
• Coolant type and capacity