Tom,

            Size, weight and location are advantageous perhaps, but as for
            efficiency I
            am not so sure.  When the water temperature is below 85
    degrees, OK
            sure.
            Marine applications are like this but they dump the BTU
    overboard
            along with
            the cooling water. In  aviation more than likely on T.O,  when
            cooling loads
            and engine stress are greatest, the water temp. is going to
    be over
            185F.

            With oil temps. at 200F + degrees, the delta T to water will
        only be 15
            degrees, 200 minus 185 degrees.  If we use an oil-to-air heat
            exchanger, the
            delta T with an 85 degree ambient air temperature would be 200F
            minus 85F or
            115F degrees.

            Heat moves towards the lower potential, so a higher
    difference in
            temperature  (higher delta T) would result in a higher rate
    of heat
            transfer
            and be more efficient.  Of course this entails designing proper
            intake and
            exhaust ducts  (Paul's forte') that insures all of those
    fins on the
            oil-to-air heat exchanger are free of insulating air boundary
            layers, and
            whole air mass moves through the duct in a timely and orderly
        fashion.
            The same criteria applies to the water to air heat exchanger.

             As for why Ford trucks would offer the oil-to-water-to-air heat
            exchanger
            in a towing application where the engine is under a heavy duty
        cycle I
            haven't a clue.  Perhaps someone could explain it to me.
     Keeping
            the engine
            oil warm in the cold north? :)


            Doug in Japan

            One factor is the small amount of heat transfered to the oil
    in most
            piston engines. Some piston engine squirt oil
            at the under side of the piston to cool them. Many aircraft
    piston
            engines do this as do some diesels. Never the less the heat
        dissipated
            by the oil is usually less than 10% of the total.

            The rotary on the other hand has this oil cooled rotor that
    forms
            about half
            of the area of the combustion chamber. This results in one third
            of the total heat rejection to the cooling system. As you
    can see,
            from this
            heat balance chart, 50 HP or 25% of the HP out of the
    e-shaft during
            lean cruise is rejected
            by the oil heat alone. At rich mixtures, typical during take
    off and
            climb out, the
            percentage becomes greater. If the oil is cooler than the
            glycol coolant it is not a good idea to transfer heat to the oil
            from the glycol.
            One needs to delay heating the oil as long as possible with
    a good
            oil to air
            heat exchanger and proper air ducting. More oil helps this
    process
            as it takes more heat to
            heat a larger quantity of oil. The difficult history of the
    Mazda
            rotary installation
            in aircraft has been mostly about keeping it cool both oil and
        glycol.

            Paul Lamar ...No rotor no motor.

        Doug,
        I'm running an oil-to-water exchanger on my 3-rotor.  I think
    one of the
        keys to whether or not this works is where you tap the water to
    feed the
        exchanger.  I drilled & tapped a 1/2" NPT on the high pressure
    side of
        the water pump housing, just prior to where the coolant enters the
        engine.  Then I returned the heated water to the engine out
    (radiator
        inlet).  By doing it this way the water temp feeding the
    oil-to-water
        exchanger is much lower which increases the delta T across the
        exchanger.   It also increases the delta-t across the radiator by
        dumping more btu's into the system.

        Paul stated that the "difficult history of the Mazda rotary
    installation
        in aircraft has been mostly about keeping it cool both oil and
    glycol."
        The beauty of using the oil to water exchanger is that it tends
    to keep
        the oil and water within about 10* of each other.   Before
    adding the
        oil-to-water exchanger, my oil temps would run much higher than the
        water temps.

        BTW Paul, I flew today and checked the CHT's.  In an economy
    cruise they
        were around 180-185*F.  The one nearest the water pump was the
    coolest,
        the one nearest the flywheel was the hottest, as you would
    expect.  One
        of these days I'll think to check the CHT's during climb.

        Mark S.
        27.1 hrs

        What was the outside air temp? How fast and long did you climb out?
        What was the climb rate FPM? What was the oil and glycol temperature
        just before you took off?

        It's still winter in Austin TX. A one degree increase in ambient
        temperature
        is a one percent reduction in cooling capacity. Let me know when you
        fly in
        100 F ambient air temperatures :) I am not saying it won't work but
        there is
        X amount of heat to be dissipated. If you put it all in the glycol
        system
        the glycol system MUST be 1/3rd  larger than it would need to be if
        it were
        just doing glycol. There is no free lunch. It is just common sense.

        Take some data and don't forget to record the ambient temperature
        and the
        climb speed. Many people quote temps but they neglect to measure or
        mention
        the out side air temperature and the climb speed.

        A marginal cooling system will work if you climb out at 200 FPM at
        130 to 150 MPH to 500  foot altitude. Texas is fairly flat in
    your area.

        Record temp out of the pump, out of the block, in the rad, OUT of
        the rad,
        in the oil water HX, out of the oil water heat HX, climb speed,
        climb duration
        and last but not least the all important out side air temperature.

        This should give everybody a clue on just how complicated this
        system is.
        That is why I wrote a book on the subject.

        The situation with an air cooled engine is not as bad as the
        rate of heat transfer from cylinder fins to air is greater and
    as the
        fins heat up beyond 400 or 500 F the rate of heat transfer also
        increase.

        With a water cooled system there is a real limit of how hot the
    glycol
        can become before catastrophic boil over. The air/oil cooler is not
        as bad
        as the boiling temp of oil is much much higher than that that of
        glycol.

        Paul Lamar ...No rotor no motor.

    Paul,
    Here's a little more data (from memory).

    Climb was at 100 kts [115 MPH] , 1100 fpm from 520 ft to 1500 ft,
    then 800 fpm up to
    3000 msl at 115 kts [132].  Once I reach 500' agl I start reducing
    the prop
    rpm.  For yesterday's flight prop rpm was set at 2300 for takeoff.
    During the 800 fpm climb the oil temp was up to 205 and water temp was
    195.

    OAT on the ground was 75, it was a beautiful, cloudless day.  (Today
    they're predicting a high of 87*... so much for the Texas winters)
    I don't have all the other readings as I don't have that many inputs on
    my EFIS.  But I do monitor the oil temp out of the engine (pre oil/air
    cooler) and oil temp pre oil/water cooler.

    One thing I'm not sure you realize with my cooling system is that I
    still have the oil-to-air exchanger installed.  I was hoping that there
    would be enough capacity in the water radiator to handle the whole
    cooling load, but that was not the case.  The oil/air exchanger is in
    series with the oil/water exchanger.  So, I left it in place and feed
    the hottest oil to that cooler first, then run it through the
    oil-to-water cooler to bring it down another 25*.  It was pretty obvious
    from the start that I had an excess of water cooling capacity and a
    deficiency of oil cooling.  So, all I'm doing is transferring some of
    the load from the oil to the water.  If I could increase the cooling
    capacity of the oil/air exchanger I probably wouldn't need the oil/water
    exchanger.

    Mark S.

    I went back and checked some old messages prior to installing the
    oil water
    HX but you never mentioned OAT or climb. Do you remember what that
    may have
    been?

    "To answer your question on water temps; the water temps were never
    a problem.
    They would stabilize around 135-150, depending on MAP."

    Sounds like your glycol system was very effective if not over kill.
    Do you recall the size of the rad?

    Paul Lamar ...No rotor no motor.


Paul,
The application was Ford Galaxy (probably w/390ci engine, but not
stated).  Core size is 18 x 22.5 x 2.5, best I recall.  Initial flight
was in August and the temps were in the mid 90's.

Mark S.


You obviously did a great job on the rad ducting. Core volume appears to
be about 1000 cubic inches where our rule of thumb call for 300 cubic inch
per rotor or about 900 at the max for a 3 rotor.

What I can't understand is why the oil cooler is not working better.
Perhaps you have some air leaks in the front duct or the back side of the oil
cooler is too hot. Can you make some air temps measurements behind the oil cooler?
What brand of oil cooler is that?