Kirbert wrote: << I am highly suspicious of the Jag V12 water pump impeller.
someone hypothesize on why the Jag V12 impeller, with almost exactly
the same exterior dimensions as a Chevy V8 impeller, would have
impeller vanes configured SO differently? It seems to me that the
engines turn basically about the same rpm, have pulley diameters
about the same ratio, and push coolant through cooling jackets and
heads of similar configuration and through a radiator of comparable
configuration. Chevys overheat only when something is wrong, Jags
overheat all the time. >>
I have a theory about that, which is that since the Jag V12 is designed to
make max power at higher RPMs, and indeed to run, usually, at higher RPMs,
the impeller is designed to minimize drag at higher RPMs, which
unfortunately means less coolant movement at lower RPMs. I say
unfortunately because most of us spend our lives at lower RPMs, and the
overheat problem is definitely a lower RPM phenomenon.
My car no longer has the load of a transmission cooler, and I still see the
heat creep-up problem.
I suspect the Chevy impeller simply forces more water through the system at
lower RPMs, and hence increases cooling there, at a cost of more drag at
higher RPMs, where it isn’t noticed much anyway. Likely the single-pass rad
and the electric fans help somewhat, in that they cool better the water
moving through, but moving more water through is also a plausible remedy.
Has anyone besides Kirby either replaced the impeller with a different
design, or gone to a different (high-flow) waterpump such as the EWPs?
'92 XJS Conv. 5 sp.
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