Radiator Cap--flow rate through radiator

Terry Martin terry_martin at mindlink.bc.ca
Wed Oct 15 21:23:57 GMT 1997


John Hess wrote:
> 
> Don't forget that the amount of heat transfer (both in and out) are
> somewhat dependant on differential temperature.  The greater the
> temperature differential between radiator temperature and ambient, the
> larger the temperature drop within the radiator.  Water moving too fast
> will not sink up as much heat in the heat developing portions of the
> engine AND will not cause as high a temperature differential in the
> radiator (between radiator and ambient), resulting in higher engine
> temperatures, even when the coolant temperature reading is lower.
> 
> I once had an MG that ran at it's coolest (per the temperature gauge)
> when there was no water in the radiator.  Don't get caught up in coolant
> temperature readings as the sole source of information.
> 

I don't know if I missed it, or everybody else did, but all of these
back&forths assume a constant rate of flow through the block and
radiator. I'm no radiator expert, but I've yet to see one that does not
hold more coolant than the relevant block volume. By that I mean the
coolant picking up the heat in the block, not sitting around waiting to
get out. Only a partial fraction of the total block volume is in contact
with the block at one time. A much higher fraction of the total radiator
volume is in direct contact with the radiator flutes, and there-fore you
have a vastly increased heat dump, even with no air flow, than you have
heat pickup in the block. In can not be otherwise or it would simply
circulate hot water. As for cavitation, which is simply put, drawing a
vacuum in the middle of a body of fluid, I would guess that would be
more of a problem with boat props, than either engine flow or pump flow.
It's no accident that cooling systems are run pressurized. It
significantly raises the boiling point of an already chemically raised
boil point coolant,
and makes cavitation within the block practically impossible. Most of
the pumps I've seen "push" the coolant with an impeller, they don't
"suck" it, and there-by it raises the pressure within the pump, with the
same result on boil point and cavitation.

Terry





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