The Water Pump
The Bearing
The Water Pump by Robin Rich

The Automotive Water Pump

In general the main purpose of the automotive water pump is to circulate the coolant of the cooling system of a water-cooled engine.

  • The pump normally consists of the following parts:
  • The pump body which will also contain the outlet.
  • The impeller which initiates the stirring or circulation.
  • The seal which separates the coolant from the bearing/s.
  • The bearing, which facilitates the rotary motion, needed for circulation.
  • The pump flange which will house a pulley to drive or rotate the pump.

The automotive water pump normally gives reliable service for surprising extended periods of time.  Like most things mechanical it will warn you when it needs attention or replacement.  Be conscious of leaks and noises.

The heart of the pump is the mechanical seal.  When the seal is not functioning properly coolant will leak past it.  To prevent the water reaching the bearing/s the pump body has a drain hole and the water should drain from this hole.  Invariably by the time the seal goes this drain hole is clogged up.  Soon the bearing/s will be running on a mixture of coolant and grease.  The end result should be obvious.

There are other factors that influence the life of the pump.

The condition of the coolant i.e. it should be free of contaminants like rust, scale or any other suspended fine particles.

The drive belt/s should be in good condition and correctly tensioned to eliminate undue loads on the bearings.

The drive pulley should run true and concentric for the same reason.  Normally a fan is secured to the pulley.  This should be balanced and also run concentric with the pulley.  It is not uncommon to see a modern automotive water pump with a drive pulley having two or more V-grooves.  Again more load is placed on the bearings.  To aggravate this situation it is surprising how unnecessary heavy some of these pulleys are.  So when the water pump needs attention or replacement have some respect for it.  After all it is as important and vital as the engine's oil pump.

The automotive water pump was probably not designed to be rebuilt/overhauled. By the nature of its design the early pumps needed periodic maintenance i.e. tightening the gland follower of the stuffing box and replacing the gland packing.  Normally these pumps had bushes for bearings.  These pumps were probably overhauled for economic reasons more than anything else.  The stuffing box of these pumps is the equivalent of the modern mechanical seal.  The difference though its main function was to prevent the coolant from leaking out of the pump rather than keeping it away from the bearings.  The design of the stuffing box actually calls for it to leak the occasional drop.  This helps to lubricate the shaft.

Soon the mechanical seal was literally put under pressure as cooling systems were pressurised.  The non pressurised cooling system is very tolerant towards the condition and efficiency of the mechanical seal but not so with the presurised system.  It is for this very reason that it is of utmost importance that the stationary and rotating faces of the seal is in perfect condition. When the condition of these faces deteriorate is the time when the pump is bound to reach its expiry date.

The mechanical seal and sealed bearings further forced the automotive water pump to become part of the "Kleenex" Philosophy – use it and throw it away.  The modern automotive water pump is just that, some to the extent that it just is not an economic proposition to rebuild them.

When attempting to rebuild an automotive water pump the most difficult part is to dismantle it without destroying it.  Once dismantled it is relatively easy.  There are the cases where the rebuild is not a matter of clean, machine and assemble. In such cases, to eliminate any guesswork, it is best to measure the components and prepare a drawing.  This practice also contributes to a high success rate in rebuilding pumps.

Prior to dismantling a pump for a rebuild the pump body, whether in cast iron or aluminium, is inspected to verify that its condition warrants a rebuild.  The screw threads in the pulley are cleaned by tapping.  Critical dimensions needed for assembly are taken.

Once the pump has been dismantled the body is thoroughly cleaned.  Particular attention is given to the machined faces, which accommodate the mechanical seal.  Likewise is the recess for the ceramic insert at the face of the impeller treated.  If the design of the impeller does not include a ceramic insert then the working face of the impeller is machined and finished to a surface texture of N6 or better.

Propriety water pump spindle bearings are used.  When deep groove ball bearings are replaced then only quality new bearings having Normal or C3 radial internal clearance are used.

To be able to use commercially available mechanical seals often necessitates some modification i.e. an adapter for the seal.  All machining is done accurately to ensure the correct fit of mating parts.

Any modification carried out caters for the possibility of rebuilding a rebuilt automotive water pump in future.  This not only makes the second rebuild much easier but should also be cheaper.

Each rebuilt water pump is supplied with a new gasket or gaskets as the case may be.  

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