Del Johnson wrote:
I have some questions about the cooling system and would like to float my
design by the group before proceeding.
Attached is a drawing that depicts the proposed system. The red lines
indicate the pressure side of the cooling system (outflow from the pump) and
the green lines reflect the low pressure side ( return flow).
I would like to use the Mazda thermostat, to control the re-circulation of
coolant in the water pump during cold operating conditions. The high
pressure output line to the radiator will be through a welded on tap that is
located below the thermostat so there should not be any restriction in the
flow to the radiator. The primary reason for using the thermostat is that I
would like to use an exhaust augmentation system which precludes using a
cowl flap to regulating the exiting cooling air.
I'm tight on vertical space in the cowling. Placing the radiator cap
immediately above the thermostat might require a small bump in the cowling.
I therefore included a separate small reservoir that has the pressure cap so
that it can be located elsewhere under the cowling. This unit also contains
one or more bleed line taps that will purge the system of steam vapors
should the system overheat. I included in the design a low pressure check
valve that will prevent the high pressure coolant from backflowing to the
low pressure side. Any buildup in steam pressure will open the valve.
What is the minimum size (volume) of the overflow bottle?
How many lbs of pressure should the overflow bottle hold?
If you are using standard car overflow bottles which make / model car
overflow bottle are you using?
Any comments or suggestions on the design that I presented?
That looks like it will work Del but you will be giving away some
MPG and speed by using a thermostat instead of a cowl flap to control
engine temperature. A cowl flap will reduce the cooling drag
when max cooling is not required during cruise.
The pressure in the system is about 25 psi when a 25 psi pressure cap
is used. I recommend a 25 psi pressure cap as it increase the all important
boiling temp. If the coolant boils that is a catastrophic engine failure IMHO.
Something around a gallon seems right for a pressure bottle.
Here is the system I recommend. Note the pressure cap controls the pressure
on the pump inlet side. There will be pressure drops throughout
the rest of the cooling system.
The Corvette has a nice metal pressure bottle. I had Ed Klepies weld
one up for me so I could use highly reliable AN hose. More rotary
powered airplanes have crashed by using low automotive quality plumbing
than for any other reason.
Paul Lamar
Paul, Has anyone done a flow schematic with the inclusion
of the pressure bottle? Am I correct in saying that the
"pressure bottle" is actually a header tank? Do you intend
am overflow tank as well, or a coolant recovery tank if you
will? I am working on my radiator locations and tank placements.
I haven't to this point had enough hands on
time to get a good feel for routing. Do you, or has an ACRE
subscriber done a flow layout? Anything you have will be helpful
as I start getting into the plumbing layout.
Thanks,
Bill Jepson
Yes it is a header tank. You still need a coolant recovery tank. Not
shown in the 3D. I guess I need to add that to the 3D.
We discussed a real coolant recovery system a few years ago. I think we
concluded you need a 50 psi pump to get the coolant back into the engine
while the engine is still hot and running.
If your rad is under the engine a two pass rad works well as then the inlet
and outlet are at the back of the rad close to the water pump.
You will need small vent lines from the front of the rad and from
the front of the engine back to the top of the header tank. I'll add those
to the 3D as well.
Paul Lamar
Paul,
if you purge your system you shouldn't need a pump to
"refill" the system under operation. The volume inside
the system should only increase pressure until the cap
max is hit then outflow into the recovery tank. If the
recovery tank is also pressurized with the same cap, the
valve in the header tank should allow refilling the radiator
system when the system cools. Or did I miss something?
Bill Jepson
We were discussing what happens when a significant amount of
coolant escapes to the ambient pressure over flow tank and
perhaps on overboard in the form of steam.
It will not be sucked back into the engine until the engine
cools. The typical pressure cap has two valves in it. The
first is the pressure release valve set to about 24 psi. The
second is a one way valves that allows coolant to flow out of
the over flow tank back into the now low pressure header tank. This
won't work until the engine cools down the coolant in the engine
contracts and causes a low pressure in the engine that sucks
the coolant back out of the overflow tank.
The idea was to carry a third emergency tank of fresh coolant
with a high pressure to pump to pump fresh coolant back into the
hot and still running engine to compensate for the slight leak
(or whatever) to get you to the nearest airport.
Paul Lamar
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