Paul,

  Good news!  After spending many, many months (years) trying to get my oil
  temps down, I finally discovered that the problem was a defective oil
  cooler.  It appears that the only oil cooling was from the oil/water
  exchanger.  While temps were too high for comfort, especially during
 summer,
  it did cool the oil well enough to keep me flying throughout the Texas
  summer.  After just recently discovering the defective cooler, I replaced
 it
  with a Modine of similar size & style and flew it for the first time
 today.
  WOW!  What a difference, possibly enough to remove the oil/water exchanger
  altogether (more testing is requried).  Addimitedly, the OAT was in the
 mid
  40's, the return oil temp was down in the 150*F range, when it had been
  around 210 - 240*F.  On today's flight, in cruise configuration, the
 coolant
  was 165-170 with cowl flap closed.

  Also, it appears that Lynn Hannover is correct (big surprise) about the
 best
  horsepower being produced at around 160*F oil temp.  I saw an extra 11
 knots
  IAS today over my typical cruise speeds.  I'm sure it wasn't just my
  imagination as the fuel flow was also higher.  (Gotta take the bad with
 the
  good.)

  So, if you want to go fast(er), work on reducing those oil temps.

  Mark S.

  That has happened before. Was it a 2nd gen Mazda cooler?
  What was wrong with the old cooler? Was the oil thermostat still in there?

  Paul Lamar


 If you hadn't installed the oil-water exchanger, you would nearly
 immediately known that your primary cooler wasn't working at all..


 Matt-

 We need to do a check list for this stuff as this type of oil cooler
 failure  never occurred to me. Do's and don'ts. The second gen cooler that
 works so well is a two pass.

 Paul Lamar

Paul,

A checklist of possible causes of poor cooling would be a beneficial tool
for many builders.  When trouble-shooting a problem, it is easy to "assume"
things to be true that are not, such as in my case of the swollen oil cooler
end tanks.

I don't know exactly when the oil cooler failed, but I feel that the
oil/water exchanger allowed me to continue flying, albeit with slightly
higher oil temps.  At least I didn't have to do an emergency landing out
in west Texas somewhere.

Also, the TES o-rings are probably the reason there wasn't any engine damage
from the higher than normal oil temps.

Mark S.

Back in the old days you could destroy a set of neoprene cooling O-rings in an instant.
I know! It happened to my brand new 12A powered RX2. I wish I had that car back. It only weighed 2500 pounds and had a lot of room in it. It is 500 pounds lighter than my RX8 with less room. Your tax money at work. This is one I saw at Seven Stock. It had a 3 rotor in it. I have a 3 rotor sitting in the hangar waiting :)

Paul Lamar