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Hi Tj
Yes, the initial design of my cooling system as well as
its components go back to 1997. Lets just say,it seemed like a good idea at
the time and having no one around to advise me differently, I proceeded as
follows:
At the time, using two GM cores I got from the junk
yard, I simply cut off the 3/8 - 1/2" aluminum tubing which were on the
bottom of this particular core configuration. Thin I drilled out the
existing holes and brazed in two AN-16 Male fittings. Since I did not have
sufficient room up front to run the coolant line connecting the two over the
Ross PSRU, I ran it under. So as you so correctly deduced, the inlet and
outlet are both on the bottom. No question it would have been better to
run the coolant in the bottom of one and out the top which would have left no
space in the core for air to accumulated.
Yes, at 22 psi the air would likely occupy even more
space, but since I do my runup with the cap off or loose, there is no pressure
during the process. So while I have never measured it and it probably
varies from one time to the next, there appears to be approx 1/3 of the top part
of each core which has air on the initial fire up of the engine - after a
complete drain and refill of the coolant system.
I must admit that the first several times of draining and
refilling coolant, not being as knowledgeable as I am now, I almost cooked the
engine, because I assumed that when the header tank was full - the engine had
all the coolant it could take. Rapidly climbing coolant temps and pinging
of hot engine cooling off soon make it clear that just because the header tank
was full didn't mean a whole lot. Of course, I noticed after each run up
that the coolant level in the header tank would decrease permitting me to put
more coolant in. That finally made me realize what the problem was - would
have been very nice to have this list around back then {:>)
After burping the system there is still small amount of
air left, but the overflow tank set gradually removes the remaining air over a
couple of flights. Then the hydraulic "lock" phenomena starts with initial
pressure of 21-22 psi immediately on engine start, dropping off quickly to
zero and then gradually climbing back to 5 - 7 psi as the coolant
heats up.
But, other than having to "clear" the air out with a
couple/three run ups to 5000 rpm, it works just fine and has since 97. I
occasionally toy with the idea of putting in simple small air bleed on the top
of each - but, like I said, it works fine and other things to do
{:>)
Sounds like your approach will avoid my burping
problem. However, Lynn has mentioned that even in the car installation it
often takes burping the engine to get the air out.
Ed
----- Original Message -----
Sent: Friday, October 05, 2007 11:12
AM
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Hi Ed,
for sure I saw your installation before (numerous times...), but I do not
recall your exact pluming.
Your description below sounds like inlet and outlet are facing
down.
At 22psi it should even be more like 1/2 the radiator with air :)
Anyway, I assume waterflow is radical enough to strip the air out in 3
trials.
My system will have a bottom inlet and a top outlet. If it doesn't fit
the outlet may exit the bottom of the tank but will have an internal standpipe
- this way there is next to no space where air can get trapped, just a small
bubble atop the standpipe, won't be big enough to cause any cooling detriment.
I still see BMW motorcycle oil-coolers mounted this way. Don't know the
exact make-up today, but the earliest ones where simple single pass bottom
feed bottom exit (cheapest solution and esthetically least disturbing), a big
problem to purge. 1/4 was useless because of trapped air...
Furthermore, if the pump had a little leak or just a long time between
runs would drain the oil fro mthe cooler and at start-up you had a fresh load
of cold air inthe cooler! As it heats up the air-bubble expands and reduces
cooler volume even more...
Best Regards,
TJ
snipped..
In my case, if I do a complete drain and
refill of the system, on the first run up the core's tanks will be hot
approx 2/3 of the way up and then they are much cooler - indicating that the
remaining 1/3 of my core is filled with air. It generally takes me 3
runups reaching 5000 rpm before I can touch the core tanks
and find them hot all the way from top to bottom. So depending on your
radiator set up that might be something you can quickly check.
snipped....
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