RE GMC 412265-D24 Water Pump

[dacarc]

This business of adding restrictors or a smaller capacity
water pump for better cooling has never made any sense to me.
Slow flow through a radiator would mean a greater differental in
inlet vs outlet temperatures. Fast coolent flow through a radiator
would mean a smaller differental in inlet vs outlet temperatures.
It can be shown that the second case radiator with the
faster flow would dissipate more BTU's per second than the slower
flow case assuming the same inlet temperatures. The faster flow
case results in a higher over all average temperature over the
entire frontal area of the area of the radiator and hence more
heat transfer to the ambient air flow. This is a simplification
because the mathematics use Calculus and are more involved.
Simarly, faster flow rates through the engine block should
lead to a more uniform temperature thruout the structure vs the
lazy slow flow case and also yield the higher BTU transfer rates
as discussed for the radiator case.
The only time high flow rates would be undesirable is
when cavitation begins. Yet, ever since I was a teenager in the
days of flat head Fords, I have always been told the myth of of adding
restrictors for better engine cooling.
Can any of you engineers out there please justify the
restrictor/smaller pump myth so I can get it straight.
Thanks; DAC 78-Royale

 

[lawrence coldren]

My observation in racing engines is in older engines that have some rust
and/or deposit buildup in the water jacket, high coolant flow rates result
in reduced cooling efficiency. I was told that this is the result of
decreased surface contact efficiency for the faster moving coolant across
rough rusted surfaces. Slowing the water pump with a larger pulley
increases the cooling efficiency. When did they last build the 455? My 2
cents. Larry

- -----Original Message-----
From: EMERYSTORA
To: gmcmotorhome
Date: Thursday, December 23, 1999 10:58 AM
Subject: Re: GMC: RE GMC 412265-D24 Water Pump

>

>
>water pump for better cooling has never made any sense to me.
>Slow flow through a radiator would mean a greater differential in
>inlet vs. outlet temperatures. Fast coolant flow through a radiator
>would mean a smaller differential in inlet vs. outlet temperatures. >>
>
>restrictors for better engine cooling.
> Can any of you engineers out there please justify the
>restrictor/smaller pump myth so I can get it straight.
> Thanks; DAC 78-Royale>>>
>
>
>Dac -- I agree with your message 100%. I have posted in the past that I
>failed to see how a slower flow could transfer more heat. The more water
>molecules that contact the hot surface, the more heat transfer. I had much
>training at the Univ. of Mich. in heat transfer and my first job out of
>college as a Chemical Engineer was to design heat exchangers for a major
>chemical company. Even though my experience was many years ago, the basic
>laws of Thermodynamics and Fluid Dynamics have not changed. I was also an
>Associate Member of the Society of Automotive Engineers for several years
and
>specialized in automotive coolants and brake fluids.
>
>It is interesting to note that apparently a lot of GMCnetters believe this
>myth but on the other hand they are concerned with smaller impellers,
stamped
>impellers versus cast iron impellers, etc. The only way that slower flow
>would be better is if a slow flow rate through very small passages would
>create so much fluid drag at the surface that the resulting laminar flow at
>the surface would result in an insulating effect. This will not be the
case
>in the GMC system. The flow rate and passage sizes that are in our engines
>and radiators would not cause this. In fact, a faster flow rate through
very
>small passages would cause turbulent flow and greater heat transfer.
>
>Any automotive engineers out there that have an opinion? My son-in-law is
an
>automotive engineer with Rousch Engineering in the Detroit area. They do
>engine design for the major companies such as Ford, Chrysler and GM and I
am
>going to ask him and will post his reply. He also did a bit of work for
>Howell last year in designing a new chip for the Howell fuel injection
system
>to make it work better for the GMC. In Howell's earlier systems they were
>using a stock GMC truck chip set that didn't perform as well.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>