Subject: [TR] 4 vs 6 vane water pump impellor

From: "Bob Danielson" <[email-masked]>
Date: Sun, 25 May 2014 21:04:25 -0400 6tdpPq/Fma17z8E4gMwgTYegYzG2g3gQso4AgdSAWi9FE1gUJf 1MdrBk6BCye3Jm0czTxxnGchfdtQrcQ/FZhVPVywNX7WTLQghV mPxZ5KmMiXfHccvvmSJVvweVImN38U/o4AMlrbmEZdgWMBOeS/ 1o509qASHH4ZdnTINy0XGXd/pQZu6aVnmRfVwVLofq4M3IXslz HgzxTo4rgC3M+JNgYBR7qs/ZmeqUb2v8yNAGNYMlnhve75/HVY 3HNPPsHYBwXrtp2lv7DUh9ZI+3rsfCz+3cPDfVwqnWiYbd4jtP IDx5ULYwc8D7MVx8+vlDbrNiXWNvJHcaiNT8yZHSy

I recently had a TR6 spare water pump rebuilt by The Flying Dutchman and one 
of his options is a 6 vane impellor. I installed the pump last week and had 
the upper coolant hose (thermostat to manifold) burst yesterday. Between 
then and now, it covered over 250 highway miles with no problems. In 
examining the hose I can see where it was full of cracks and check marks so 
the failure is probably coincidence. As a result of my problem there's a 
discussion in 6-Pack on the advantage/disadvantage of a 6 vane water pump.

One group feels there's less cavitation and more volume pumped through the 
system.

Another group feels it pumps the water through the system too fast and the 
radiator can't cool it properly so the car runs hotter. Another view was 
that with the thermostat closed it could increase the pressure and expose 
the hose as a fail point.

All speculation and theory so........ does anyone know the 
advantages/disadvantages of 4 vs 6 vane? Rimmer and Racetorations both sell 
it as an upgrade to the cooling system

Thanks

Bob

Bob Danielson
http://tr6.danielsonfamily.org/PanelBootSales1.htm
Custom Interiors & Boot Covers
http://tr6.danielsonfamily.org/FenderBlanket.htm
Fender Blankets 

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From: "Randall" <[email-masked]>
Date: Wed, 28 May 2014 03:16:49 -0700

> advantages/disadvantages of 4 vs 6 vane? 

Water pump design is an extremely complicated topic, even for a pump running at constant rpm, let alone with the widely varying rpm,
head and flow parameters that are inherent in automotive cooling systems.  And the number of vanes is a relatively minor variable in
the performance of the pump.  Things like vane shape, clearances, housing shape and so on have a much larger effect on results.  So,
my opinion is that it is impossible to state categorically that a 4 vane pump is better or worse than a 6 vane.  

In other words, this discussion is futile, until and unless someone gets a sample of each specific pump and does some specific
performance tests on it.  Even then, it is going to be hard to say which is "better", since I've never seen any evidence that lack
of water flow is a problem with our engines.

One thing, though, there is no such thing as "moving the water too fast so the radiator can't cool it".  A long-persistent myth,
perpetuated by those who slept through high school physics (or took auto shop instead).  What can happen on cars with the pressure
cap on the high pressure side of the radiator (like the TR2-6) is that the pressure differential across the radiator rises so high
that the cap opens and lets coolant blow out the overflow.  THEN the engine overheats, due to lack of coolant flow (and coolant).
I've also seen non-TR engines where the hose on the low pressure side would literally suck closed, blocking off the flow.

My own experiments with 4 vs 6 (on a TR3 motor) showed no measurable difference in cooling performance.  But I didn't bother taking
any flow or pressure measurements.  With a stock 4 vane pump, and adequate airflow through the radiator, the engine stays cool even
in 115F weather (which is more than the driver can stand).

Randall