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There are two kinds of cooling systems (kinds of "expansion tanks") as far
as I know: 1) the one most people think of and talk about is a
non-pressurized expansion tank that gets fluid when pressure "burps" past
the radiator cap. That is the kind where the fluid gets sucked back into
radiator AFTER engine shutdown (IF there are no leaks anywhere to let AIR
suck in - which would prevent sucking fluid from the expansion tank).
2) the 1998 or so Ford Contour system (and others) where "expansion
tank"/"header tank" is pressurized (the pressure cap is on the tank, not the
radiator), and it has a tube going down out of the bottom of tank to a T
fitting at bottom radiator hose; also there is a tiny "air bleed line" in
the highest part of the engine (somewhere in the head at the top of the
water passages) that slopes UP into the bottom of the "pressurized expansion
tank/header tank" - any air at top of engine would flow up into the tank and
would be replaced in the head by gravity flow of coolant into the system -
coolant level in the expansion tank is slightly above the highest point in
the head's coolant passages.
This "Contour" system would be perfectly safe to have the "coolant level
switch" in the tank. There would be none of the dangers cited for systems
that have the NON-pressurized exp tank.
- Also, none of the "burping" several times after filling as there is
with the "non-pressurized" tanks - in Contour system, you fill thru the
"expansion tank" - fluid runs out bottom and fills entire radiator-engine
block system from the bottom up, with (theoretically) NO air trapped in any
radiator or engine part as the fluid rises to top of head and then up into
bottom of tank. When fluid in the tank starts to rise, you know th engine
and radiator system is full. Of course, there could be "pockets" somewhere
or a hose that runs up and back down slightly where air could be trapped -
so an engine run should move the air to top of system, where it would bleed
into the bottom of pressurized expansion tank, and "burping" would be done.
- This is what I'm designing for my RV-6/13B aircraft.
David Carter
----- Original Message ----- From: "Charlie England" <ceengland@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, March 19, 2005 10:03 AM
Subject: [FlyRotary] FD coolant level sensor?
Bulent Aliev wrote:
> On 3/19/05 10:06 AM, "Russell Duffy" <13brv3@bellsouth.net> wrote:
>
> Greetings,
>
> I'm looking for ways to put a coolant level switch in the engine,
> and remember that the FD had a level sensor. I never looked it one
> of these before, so I'm wondering how it worked. Does anyone have
> one they can look at, or perhaps send me if you don't want it?
> Does is have some sort of float in it? I have an extra 1/4" NPT
> hole in my upper water pump housing, which would make a great
> place for a switch, but I haven't found one that seems like it
> would work there very well. Did the FC use level switches?
>
> Thanks,
> Rusty (top secret lower cowl being test fit today)
>
>
> Hi Rusty, I don’t think coolant level switch should be on your water
> pump. If the coolant level drops there, it is too late. The pump will
> cavitate very very soon. (assuming is the stock pump). I would install
> it in the expansion tank or overflow tank. When the coolant drops
> there you will have more of a chance to head back before the pump gets
> exposed.
> Buly
The 2nd gen car that's dead in my hangar is dead because I got dependent
on the 'raise the dead' buzzer that went off when the sensor *in the
overflow tank* sensed low coolant. When the upper tank on the radiator
cracked & lost coolant while driving, the overflow tank still had plenty
in it & I never got the buzzer.
This brings up a potentially significant point. Most folks say to use
system pressure to detect leaks. I can't say from experience that it
works, but I can say that a level sensor in the catch tank *won't* work
to detect in-flight problems because the level there isn't likely to
drop until the system cools & tries to suck coolant back from the
reservoir.
I'll try to take a look at how it works for you some time today when I
take a break from doing my taxes. (Weather induced major change of plan
from flying down to St Elmo for lunch & SQ2000 inspection. Sorry, Paul.)
Charlie
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