Tracy said: <snip>  Other changes included adding <snip>and external
stiffener on water pump inlet hose (to prevent collapse in the event of
negative pressure).

Yvon said:   Allo Tracy. I have internal stiffener on my 1986 13B  water
pump inlet hose and this is the first time I hear about external stiffener.
I would like to try that. Where can I get it? Please. Yvon.
- - - - - -

David asks:  Is there anecdotal info or hard examples of the inlet
hose-to-water pump collapsing?

If so, then I'm wondering about the causes - and implications for "our"
design(s) of 13B cooling system.

Extreme case #1:  Water pump is being spun at X rpm ("normal range for
takeoff") but on a test stand with no engine or radiator, just a stock 1.5"
dia auto hose on outlet that wraps around with other end of hose on inlet of
pump.  This would be the "minimum resistance" or "minimum restriction" to
flow out of the pump and into the pump - just the restriction of friction in
the hose of X length and Y flow and the necessary 360 degree curve in the
hose, which, not being straight, would add some slight resistance.

Mid-range (baseline) case #2:  Water pump is on engine, with std 1.5" ID
hose from pump to engine.  Coolant flows through 13B coolant passages, comes
out engine into another 1.5" ID hose, into a radiator inlet tube/bung for
1.5" ID hose, and through a "typical" or "stock Mazda" radiator, and out the
radiator into another 1.5" ID hose back to the water pump.
   -  If we could measure pressure at the pump outlet, and at engine
outlet/radiator inlet, and at radiator outlet/pump inlet, as well as ambient
air pressure OUTSIDE the hoses, then we'd see if there was any "negative" or
"collapsing" net "net external" pressure on the pump inlet hose.

Other extreme case #3:  Put a 5/8 inch ID restrictor between the engine
outlet and radiator inlet (could be the radiator inlet of some installations
currently flying) and again measure the pressures and see if there was an
increase in "collapsing" force on pump inlet hose.

Hypothesis:   I think restrictions below the stock 1.5" ID hose and
associated fittings, as well as series A/C cores instead of parallel cores
would decrease flow and increase pressure drops and increase pump inlet hose
collapsing forces.

I also think flow should be "maximized" through the "closed cooling system",
not restricted by "convenient" hose and/or fitting sizes on the A/C cores,
especially if they are in series.

David