As you say, Al, there are stories, rumors,
misinterpreted data and occasionally actually facts. I guess my old
brain cells are surely declining, but I just can't get it out of my
head that EVANS is rather like - a band aid- for a marginal cooling
system.
I do agree catastrophic boil-over is something to
be avoided. But, IF the problem is your system can't keep up with your
heat dissipation needs, then the system needs to be fixed, substituting a
coolant with less heat carrying capacity and raising the operating
temperature just does not seem the right course of action - in my
opinion.
Responding to you question about the rotary
limitations. In the rotary's case, the old conventional wisdom probably
goes back to data published by Racing beat way back when - I still have
the article. To quote excerpts from the article:
"...oil temperature entering the engine should never be allowed to exceed
210F.."
" ...Under normal conditions the engine water
temperature (exiting the
engine) should never exceed 180F. However, engine damage is not likely to occur even up
to 200F - IF the temperature rises slowly. If
it rises quickly, however, due to broken hose, lost fan belt, etc., engine
damage is likely."
I suspect that later model engines are not as
sensitive and I have had my coolant as high as 240F for very short periods and
oil as high as 220F. I could not tell of any adverse effects -
however, as soon as I detected the excursion I quickly backed off the
power. My normal Max is 200F for the oil and 220F for the coolant, but
again only on climbout at high power on a hot day. I suspect
as long as the coolant and oil are still circulating and carrying heat
away - you have more of a margin than if the coolant suddenly disappeared
through a broken hose {:>). Not being in a frigid area, I
use a 25/75 EWG mixture rather than the 50/50 normally quoted.
So a coolant like the EVANS which can indeed operate at
higher temperatures with much higher boiling point than water,
would not appear to offer much to us Rotary folks as our engine (if you can
believe what the experts claim) simply can not tolerate the higher operating
temps.
If the fluid can not carry as much heat per unit volume
as H20, then it sure seems to me that you would need to increase the flow rate
of the rotary pump to compensate. While raising the temperature of
the fluid alone will indeed transport additional heat, lets look at what it
takes. Assuming the mass flow is the same (no increase/decrease in
coolant flow rate) then looking at the Cp of pure water, 50/50 mix and
NPG we have
Cp H20 1.00 Cp 50/50 0.82 Cp NPG 0.66. Just
to make my point, if 180F is the steady state temp for an system with pure H20
then using Evans at the same flow rate, you would need to raise the
temperature from 180F to (1.00 - 0.66)/100 by 34 % or from 180F to 240F to
remove the same amount of heat.
But pure water is not a practical cooling fluid
(corrosion, etc), so taking a common 50/50 mixture we have (0.83 -0.66)/0.83 =
20% or from 180F to 216F and that is to keep the heat removal the same.
If the heat load (50/50) climbed to 200F then the Evan's equivalent
required would be 240F.
However, if we increase the coolant flow
rate by 20%-24%, then Evans can transport the same heat load with no
temperature rise. IF I were going to consider using it in a rotary, I
definitely would attempt to increase the flow rate. But,
I don't know how the different viscosity of the Evans fluid would
affect the caviation point, etc - I suspect that it would lower
it. Seems you can ever affect just one factor when you make a
change{:>) But, at least, an increase flow rate may keep the
operating temp point below a critical maximum.
So if you engine can tolerate the increase operating
temps then I agree Evan's offers some benefits as can be read on their
website.
However, the higher operating temperature point stresses
the entire system and in the case of the rotary is likely to
put it into a very questionable operating regime. At
least,that's the way it appears to me.
FWIW
Ed
----- Original Message -----
Sent: Friday, January 05, 2007 10:20
AM
Subject: [FlyRotary] Re: Ideal
cooling
Trying to make an inadequate cooling system
functional by using a different coolant is simply not going to work, but
people keep trying. If pure water is not doing the job, then using
liquids with a lower heat specific is only going to make it worst.
The Egg guys have been very successful using the Evans coolant. The
fluid is less efficient, so it inflates the operating temperature. But it
also brings a new very high boiling point to the party. So instead of
operating at the normal 200F temp, they operate at 215F. But the boil over
temp is way up there...I forget, but something like 260F or so. As a result,
they end up with greater safety margin. A very sound decision for their
installation. This because boil over is sudden, catastrophic, and
essentially irreversible. When it blows, it blows.
Rumor has it that the same solution on your engine would not add safety
margin, but actually reduce it. I'm skeptical of that personally,
but don't have facts to evaluate. It just sounds fishy that there are
components so sensitive to a mere 15F change in temp. I know how these
theories can get started and hang around for lack of facts. So I don't know
one way or the other, just skeptical.
But here's the cool thing. We tend to think along the lines of "What
can I do to improve cooling? What can I do?" But this Evans brings a new
tool to the party. It's a great way to determine if you have flow volume
problem. If you have inadequate coolant flow, Evans dramatically negatively
effects you cooling. I've measured, logged, and tested tons of cooling
concepts. Deliberately overheating engine, stuff like that. Tracy's data
strongly suggests local boiling. (Bills? observation). Trapped air or low
flow are leading causes. I strongly suspect low flow due to line
restrictions. I think we've got lot's of guys operating with 70% less flow
than the engine normally sees, and that puts them right on the edge of this
problem.
FWIW.