Jeff,
Thank you for posting
the photo and description.
My comment concerning
the effectiveness of the thermostat in the Mazda oil cooler was with
respect to keeping the temperature of the oil returned to the engine from being
too cold as opposed to keeping it from getting too high. The initial
"C" on the side of the aircraft and the attention to
sourcing cabin heat indicates to me that keeping the oil temperature up may be
a concern at times.
As the oil temperature
rises, the Mazda oil thermostat doesn't open. Instead,
it forces oil to pass through the core by closing a passage. That
passage initially allowed most of the cool oil to bypass the core. The
thermostat attempts to keep the oil temperature leaving the cooler at
about 160 degrees. If the OAT is such that the Mazda oil cooler is
capable of maintaining the 160 degrees, the second oil cooler downstream of it
will drop the oil temperature considerably lower than this. As a result,
the temperature of the oil returning to the engine will be lower than intended
and vary with OAT.
Where are your oil and
coolant temperature sensors located?
The restrictive nature
of the Mazda oil cooler is not good for several reasons:
At RPM capable of
maintaining flight, at least 6 gal/min of oil is being pressurized to about 150
psi and then dumped through a restriction directly back to the oil pan.
This consumes mechanical energy and puts additional heat into the
oil.
Also, for a given
amount of heat transferred to the oil by the engine (given power setting) and a
given temperature of the oil returned to the engine (say 160
degrees), cutting the oil flow rate through the coolers in half
requires approximately a doubling of the drop in oil temperature
produced by the coolers. This means that the oil temperature in the pan
is significantly higher than it needs to be.
Finally, the higher
pressure and temperature of the oil at the oil pump outlet may increase wear of
the pump, drive chain, and sprockets as well as increase the risk of failure of
the hose connecting the oil pump outlet to the oil cooler as well as increase
the risk of failure of the front cover o-ring. I don't know if
the Mazda oil cooler had been installed when your hose failed.
I have attached a plot
of the interaction of the coolant and oil systems for a Renesis engine on my
test stand. The ducting for the oil cooler and radiator are completely
separate and not enclosed in a cowling. The air flow through each them is
generated by the prop slip stream and controlled by a door in each exit
duct.
With the doors
positioned such that the oil and coolant were both reasonably stable at about 210
degrees, the radiator door was then opened fully and the oil cooler door
was left unchanged. This resulted in a coolant temperature drop of
about 60 degrees and a corresponding oil temperature drop of at least 20
degrees (the oil temperature was still decreasing).
Then, with the doors
again positioned to give about 210 degree oil and coolant
temperatures, the oil cooler door was fully opened and the radiator door
left unchanged. This resulted in a oil temperature drop of about 50
degrees and a corresponding coolant temperature drop of about 10 degrees.
I would expect a
similar oil and coolant interaction for a 13B. These are just my
observations and I leave it to you to decide if the interaction is
significant enough to be useful.
RV6A,
1986 13B NA, RD1A, EC2
Hi Steve:
The photo from May 8
was of previous setup and that BLUE HOSE (Twist-Tite) is what departed my
engine 3 years ago … that heat box was installed during winter
months … attached is a photo of right-side, present-day setup. The
Cabin heat will now be scavenged off the radiator outlet plenum –look
below the oil cooler. My Fluidyne oil coolers (DB-30416?) are only 2/3
size of your DB-30618. I’m not sure why the Mazda oil cooler will
not aid in oil temperature control as it seems to be doing so at present.
During ground runs the Mazda cooler is cold while the Fluidyne is warm …
during both flights so far, the oil temperature was stable at 160F while the
water temperature rose to 210F; after shutdown the temperature of both oil
coolers was the same as discerned by touch, so at some point the Mazda
thermostat must have opened. I wish I could drive over and talk to you
in-person as it’s hard to get all these details down in writing
… I like having extra oil cooling as excessive oil
temperature can damage the oil seals; excessive water temperature is not good
but the lesser of two evils.
The 13B is odd in
that the two fluid temperatures seem to be very disconnected. I’ve
managed to get control over the oil but not the water so far; however, from
previous readings I believe even if the water jacket temperature was cooler
that it would not necessarily mean a reduction in oil cooling capacity could be
achieved - I have never experienced that luxury.
Jeff
Wag-Aero 2+2, 1988
13B NA, RD-1C, EC2