The way I was visualizing it, if you have a bottom inlet then you
would have a top outlet and vice versa.  I agree with what you are
saying, but suspect you might get better distribution through the
exchanger if the input were on the bottom.

I learned the ineffectiveness of plumbing a heat exchanger wrong with
the heater core on my old '52 Ford.  Since radiators outlets were on
the bottom and inlets on the top, I reasoned that the heater core
should be the same.  As soon as the water level in the system got a
little low (and it always did), the heater would only blow cold air.
After switching the hoses around, water going in the bottom would
always fill the core to the top outlet and the heater worked just fine
even with low water in the cooling system.

Bob W.

On Tue, 11 Nov 2008 18:00:32 -0500
"Thomas Jakits" <rotary.thjakits@gmail.com> wrote:

> Hi Bob,
>
> thanks for your reply!
>
> In both installations the oil-cooler is above the oil level by a good
> margin.
>
> In my opinion the inlet position is not the critical issue, but the
outlet.
>
> As the oil slows down considerable in the inlet tank, it may (or not)
loose
> the ability to push all the air out in front of it.
> If at the initial filling of the cooler after start-up (or opening of the
> thermostat) air gets trapped at the top of the cooler, this air never gets
> pushed out, just compressed to oil pressure values.
> With a top outlet, the air has no choice but leave the cooler through the
> outlet....
>
> Am I way out there ?????
>
>
> thjakits
>
> On Tue, Nov 11, 2008 at 2:46 PM, Bob White <bob@bob-white.com> wrote:
>
> > Hi Thomas,
> >
> > If the oil cooler is below the oil level in the bike, I don't think top
> > or bottom inlet will matter too much.  If it's above the oil level in
> > the pan, then bottom inlet will ensure the cooler is always full of oil.
> >
> > My 2 cents and that's probably more than it's worth. :)
> >
> > Bob W.
> >
> > On Tue, 11 Nov 2008 14:27:00 -0500
> > "Thomas Jakits" <rotary.thjakits@gmail.com> wrote:
> >
> > > Hi all,
> > >
> > > I know this is a rotary and aviation list, but there is a lot of
cooling
> > > going on here, so I just dare to ask a OFF TOPIC - no pics, so it
should
> > > load quick too :)
> > >
> > > I would like to ask specifically* Lynn Hanover*, but if anyone else
knows
> > > something too, please let me know!

When the inlet and outlet must be on the bottom, the cooler needs to be long
in tube length and short in tube count. Like a stock Mazda cooler or an MGA
cooler. This keeps trapped air exposed to fast moving oil. Few tubes means
higher velocity. And trapped air is minimized and not such a big problem.

Where the tube count is high, and the tube length is short large amounts of
air may be trapped in the upper tubes, while hot oil uses the lower tubes.
When oil pressure is very high and velocity improves through the cooler,
much of the air is moved out of the cooler and appears in the pan or reserve
tank.

Whenever oil coolers are mounted, no matter the location of the inlet, the
outlet must be as high as possible. Oil in a piston engine foams and becomes
an insulator. It becomes compressable. It begins to act unlike a lubricant.
Engine parts run hotter. Air entrainment adds volume. So the sump may appear
over filled. The one motorcycle seems to have it right with inlet and outlet
on top. When the cooler has to be up and down, then inlet at the bottom is
of course required, because the outlet *must* be on top.

The foaming problem in the rotary is worse, due to the two oil jets
squirting oil into the spinning rotors. Multi grade oils add to the foaming
problem because of long polymer chains that link up when heated. A straight
weight oil foams less than multi-grades. Racing oils even less because they
have more anti foaming agents than street oils.

I find water cooling far less difficult. The in at the bottom out at the top
seems less important, as water gives up air bubbles readily.

Lynn E. Hanover