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Water leaking from water pump drain hole.

Root Causes

  • Foreign materials in the coolant, such as dust and/or rust, damage the surface of carbon and ceramic faces of mechanical seal.
  • Excess liquid sealant and/or glue gets into coolant to damage surface of carbon and ceramic faces of mechanical seal.
  • Over heating caused by the breakage of thermostat for initial leakage.


  • Coolant is to be checked and changed regularly according to manufacturers schedule
  • Liquid sealant should be applied sparingly within the manufacturers specifications.
  • Check if thermostat works properly
※Initial leakage should stop within a few minutes once water pump start working.


Water leaks from the mounting surface of the water pump.

Root Causes

  • Foreign matter remains on the engine installation surface.
  • Installment without correct coating of liquid packing if required.
  • Insufficient or incorrect tightening torque.
  • Some bolts are not seated well.
  • Due to using liquid packing, sealing capacity of O-ring is compromised.


  • The installation surface must be completely free of any remains from previous mounting and should be carefully cleaned to avoid damaging the surface.
  • Gasket needs to be coated with liquid packing on both faces.
  • Tightening torque needs to follow the standard of each car maker.
  • The water pump does not need liquid packing if an O-ring is used.
※GMB Gasket needs to be thin-coated with liquid packing on both faces.


(1) Collapsed (2) Fan cracked on diagonal (3) Fan clutch bearing or lock damaged

Root Causes

  • Strange noise of the bearing
    ・The mechanical seal failure caused cooling water to penetrate inside the bearing
    ・Excessive belt tension (Picture 1)
    ・Excessive vibration caused by the oscillation of the fan or pulley (Picture 2)
  • Strange noise of the mechanical seal.
    ・High surface pressure of the sliding surface. (The noise will stop after initial running.)
    ・The sliding surface is dry. (The sound will stop once the cooling water lubricates the surface.)


  • The regular maintenance of cooling water.
  • To comply with the specified belt tension by each car maker.
  • Check the smooth running of surrounding parts and replace if there is any roughness or wobble.
※We cannot say for sure that water pump is the only cause because strange noises are also caused by the surrounding parts.


(1)Impeller corrosion (2)Body sheet corrosion

Root Causes

  • Freezing of Coolant.
  • Decay of Coolant due to deterioration (oxidation) .
  • Rust preventing agent is worn out by long usage of the LLC, and ethylene glycol, which is a chief ingredient of the nonfreezing fluid, changes into formic acid.


  • Using the appropriate coolant for cold districts specification.
    (Don't reuse the old coolant. Drain and refill using a high quality coolant of the density suitable for the local climate)
  • Coolant is to be checked and changed regularly
  • Replace the coolant in the radiator and engine before water pump exchange, and flush the system.


It is not possible for GMB to sell directly. GMB has a dealership system. Once you have any question, please let me know and we will be happy to guide you.


It would be a problem. To improve sealing performance, please use liquid gasket together with GMB gasketl. However please do not use liquid gasket with O-ring or metal type gaskets otherwise sealing performance will be compromised.


Yes, it is possible. Once you advise me a measured size of the joint you have, we would select.

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We will use the feedback we receive from our customers for new product development and improvement.

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