I see another picture of cavitation damage, just inside the pump inlet.
     > The water boils due to the low pressure right at the suction
    opening and
     > along the face of the vanes.
     >
     > Coolant boiling temperature AND pressure determine boiling point.
    So an
     > effective system can loose pressure and begin to cavitate the
    pump. Even
     > stock engines can do this. In a cast iron housing it may take
    some long
     > time for this kind of damage to become obvious. In an aluminum
    housing,
     > damage can be sudden. The damage may eliminate some of the
    cavitation
     > through reducing performance, but overall system performance will
    suffer
     > from a reduction in GPM.
     >
     > Sharp edges should be removed from the pump cavity. This will
    increase
     > pump performance and raise the GPM where cavitation takes place.
     >
     > It is no accident that the lower radiator hose on every car is
    bigger
     > than the upper radiator hose. The lower hose is the water pump
    inlet. An
     > effort is made to provide coolant to the suction side of the pump
    at the
     > highest volume and pressure possible. This, so the /_minimum_
    /amount of
     > pump possible can do the job. Few cars have way too much water pump
     > installed from the factory.
     >
     > Raising the boiling point with a higher pressure cap setting helps.
     > Using higher boiling point chemicals in the coolant works.
    Slowing the
     > pump a bit works. And restricting pump output works. If the
    restriction
     > is down stream from the block, then pressure inside the block
    will be
     > slightly higher, and so, the boiling point inside the block.
     >
     > I use a 5/8" restriction on the outlet of the thermostat housing.
    I use
     > a 10% ethylene glycol and a bottle of Red Line Water Wetter. the
    crank
     > pulley is from racing beat, and is smaller than stock. We shift
    at 9,600
     > RPM. No cooling grooves in the rotor housing. No cavitation
    damage to an
     > aluminum pump and housing in 15 years of racing. No cracks around
    the
     > plug holes. Never an overheat problem. 244.8 HP at 9,400 RPM.
     >
     > Lynn E. Hanover
     >
     > Water outlet with 5/8" restricter welded on.
     > The clutch discs are Lamar Engineering/Tilton
     >
     > I would not use that disk on a street car as Robin would complain
    if she
     > had to drive it :) No springs.
     >
     > I suspect a lot of damage people attributing to caviatation is
    caused by
     > low water.
     > I can't imagines the Mazda engineers designing something that
    cavatates
     > inn our rev range.
     >
     > Paul Lamar
     >



    Lynn, how many pounds of pressure/cap?
    Steve Beckham

I use a 16 pound lever cap, but Stant makes caps up to 32 pounds.  *

Lynn E. Hanover

Lynn

Just so I got this correct.  It sounds like you are pulling the cooler
water from the bottom of the radiator into the pump and from the pump
into the engine block and then it exits the block back into  the top of
the radiator through a smaller size hose.  I don't know the orientation
of your radiator whether it is stock straight up or laying at an angle.
I am curious as to where and how you located the pressure cap.

Doug in Japan

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