Re: Cooling in relation to water speed

[James Jewell <m1garand@speakeasy.net>]

All,
   There are a few other things to consider.  The analogy with "air 
across the radiator" is flawed, because in that case the system is "open 
loop" and the air is the coolant, not the substance being cooled.  The 
air is coming from an essentially an infinite supply, kept at a bulk 
temperature (at least in your neighborhood), and once an air molecule 
has heated up, odds are that it will never touch your radiator again 
until the end of time, (by which point it has sufficiently cooled or 
heated, depending on your religious preference).  Also, since air is 
already a gas, you don't have to worry about it boiling, although it 
does turn to plasma at a temperature that I can't remember and don't 
worry about.
   The question at hand is: Do we believe a company that is in the 
business of selling high-speed water pumps?  OK, that's not the whole 
question, but it is important to consider.
   Stewart argues that the longer the water stays in the radiator 
getting cooler, the longer it also stays in the engine, getting hotter, 
as if that's a bad thing.  But if the water doesn't get cool enough in 
the radiator, it is returned to the engine hotter, and closer to the 
boiling point, so in other words, running the pump faster puts hotter 
water back into the engine, so their argument is an oversimplified sales 
pitch.  What their pumps do is improve flow at idle, where small 
radiators, with stock coolant perform poorly (cavitation, pumping 
losses, etc.) and non-linearly.
   As long as the water is moving fast enough that it doesn't boil on 
the hot side, it's moving fast enough.  Above that, there are no 
textbook improvements. (it's possible that some poorly designed engines 
have "stagnant" pockets where the coolant moves through that location at 
a much slower rate than the rest of the water jacket, in which case the 
whole system flow has to be increased to compensate for that one 
location.  Poor design, or poor casting could lead to this exception)
   Methods of improving your system are :
1) increase the radiator size (not really possible in our business), or 
fan speed
2) increasing the boiling point of the coolant. 
Keep in mind that metal doesn't magically fail at 212 deg. F, but water 
boils at that temp, and the metal quickly rises to a temperature where 
it does have problems.  Most engines could run 100 or 200 deg. hotter 
without structural problems (read my Rover disclaimer below), but for 
the most part, the coolant fails before the actual structure of the 
engine.  Tricks to increase the boiling point of water include running 
it at higher pressure  (which is partially what Stewart's pumps do) or 
by adding chemicals, or both.  Some folks completely forgo water and use 
other coolants that boil up in the 300 range.

Now having said all that, the big-bore factory Rovers do crack, nearly 
every time the coolant gets above 190, because the factory was too cheap 
during the redesign to increase wall thickness between the sleeves and 
the water jacket.  It's not a structural problem, and can be fixed.  
Wildcat blocks don't have that problem, nor do the 3.5L blocks.  
Frankly, any properly designed engine can run much hotter.  Remember 
that the oil runs much hotter that 212, as do the heads, which are up in 
the 1200 Deg F range.

Let the flaming arrows commence...........
James J., agent provocateur

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