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