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