300 degree COOLANT

[Greg Hermann]

>On Oct 12, 11:07am, Bruce Plecan wrote:
>
>> >>> has anyone heard of a special type of coolant which
>> >>> boils at 300 degrees F instead of 212-250 degrees?
>> >>
>> Don't forget ya raise the coolant temp that much your oil temps
>> are going to be way high also.
>
>Everything that I've read about the Evans PG conversion is that even though
>GAUGE temperature goes up, actual engine temperature goes down due to
>reduced localized boiling, hotspotting, steam traps, etc...

No question that Evans is on the right track, just IMHO, they are going
after it in the wrong way. Using a "water wetter" (surface tension,
viscosity, and capillary action modifier) is a far better way to go.
Nucleate boiling of a liquid WILL (this is a well proven fact) pull FAR
more heat out of a given area of metal surface than any  other flow regime
of liquid cooling--period. You could run an oversize water pump hard enough
to absorb all sorts of parasitic HP, and pump the coolant likely fast
enough to erode some of the metal from  the inside of the water
jackets--and still not suck as many BTU's per unit area out of the castings
as you will get with nucleate boiling. The trick is to create conditions
where the tiny bubbles do not have a chance to grow large against the
cooled surface--steam is a pretty fair insulator-- and conditions where the
bubbles collapse very quickly and dissappear in lower temp (moving) coolant
as they move away from the cooled surface (steam bubbles also are very
effective flow restrictors).

 The ways to get this to happen are to increase the affinity (capillary
attraction) between the coolant and the cooled surface (with obvious
results), and reduce the viscosity of the coolant (which lets vapor bubbles
collapse more easily). There are so called "water wetters" on the market
which accomplish these aims. Red Line, for one, sells one. Soluble oil
(machine cutting tool coolant) is another possibility. Water is, by far,
the most efficient practical coolant available (without going impractically
heavy, toxic, dangerous, radioactive, explosive, corrosive, and/or costly).
Yes, metallic sodium, potassium, cesium, and mercury are definitely more
(thermally) efficient coolants than water, but see the previous sentence!

My philosophy is to run only as much PG antifreeze as you need to protect
from freezing in your particular climate, a good water wetter, and the rest
water. (plus a healthy dose of inhibitors) PG is not only far less toxic
than EG, it also wets most metals much better than either EG or water
(good). (This is why it is so insanely persistent about finding leaks!)
However, it is also quite a bit more viscous than water (bad), not as good
a conductor of heat as water (bad), has a lower specific heat than water
(bad), and has a slightly higher specific gravity than water (good). If you
want to run an engine hotter (for thermal efficiency), a higher cooling
system pressure (with all components designed to stand it) is a much better
alternative than a higher glycol concentration!

The item which is absolutely the most important, and the most overlooked,
in good cooling system design, is making absolutely sure that the water
pump has enough net positive suction head so as not to cavitate. The idea
of slowing down flow through the radiator to get more cooling is an
absolute CROCK! Faster flow through a radiator will always result in the
transfer of more BTU's, even though the fluid's drop in temperature in
passing through the radiator may not be as great.  The higher mass flow
will always more than make up for the lower delta T. PERIOD!! A thermostat
(or adjustable restriction) is necessary, but NOT for this reason. What the
theromstat restriction does is let the water pump build static pressure in
the coolant inside the engine quite a bit higher than what the pressure cap
is rated for under dynamic conditions--and thus raise the coolant's
boiling point at the hottest places in the water jackets when the engine is
most heavily loaded. It also lets the water pump work on a part of its
curve where its NPSH requirement is not so high. If the water pump
cavitates, you are done, the engine will overheat. Game over.

Sorry--off subject. If you want more of a thesis, contact me off list.

Regards, Greg