Merry Xmas Paul, I enjoy the range of topics that arise for
discussion and the subsequent solutions and opinions. This mailing
list proving a terrific tool for tapping a plethora of knowledge and
experience. The comments below reminded me of a discussion I had
several years ago with an Ag pilot who'd flown Cessna AG wagons. He
said one particularly hot summer he'd had trouble with excessive oil
temperature. Close to the farm he was sowing there was a large
estuary. Every four or five sowing loads would require a low pass
over the cool water to aid oil cooling. While this helped cooling it
didn't aid the economics of the job! The company engineer was
called. 'In-field' attempts to better flow through through the
cooling rads and cowls gained little, as did adding more oil to the
sump to share absorption of heat. The simple thing that did give an
instant and sustained improvement was reducing the oil to the MIN
level on the oil dipstick!!!
The logic behind that move being that with a reduced amount of oil in
the sump the same liter or quart of oil is getting to pass through
the oil cooler more times per minute. Makes sense to me and it worked
for these guys and became the summer oil level policy for the C188's
they operated. Food for thought when designing a lube/oil cooling
system.
Kind Regards Rory Gold New Zealand
I think the measurements were/are suspect :-)
Are you near Tauranga? We have a fellow there building a Long EZ with
a rotary.
Paul Lamar
I could be wrong, but the logic does not add up.
The flow rate of hot oil makes a difference in transporting heat from
the engine to air via the oil cooler, but I don't see how the same
oil, circulating at the same flow rate, no matter how many times the
exact same molecules passes through the oil cooler, can change how
much heat is transported out of the system.
An oil pump pumping 20 quarts of oil through an oil cooler per minute
can circulate four quarts of oil five times through the oil cooler.
It can also circulate five quarts of oil four times through the oil
cooler per minute.
Since heat loss from oil to air is directly proportional to the
difference in temperature between the hot oil and the air, and the
flow rate is the same, there is no reason to believe that there will
be any difference in oil temp.
If the measurement is correct, then there must be some other
condition that is not considered. Otherwise, the data would not obey
the laws of physics.
There are two periods that we have to consider. The initial ramp up
period where the temperature rises, and the constant temperature
period where the oil temp stabilizes. My email above assumes oil
temp has reached an equilibrium. However, during initial ramp up,
oil also acts as a heat capacitor so more oil can delay the time
needed for the oil temp to reach equilibrium. Therefore, we may
want a system with larger oil tank to delay the temperature rising
rapidly.
I think more oil also helps to preserve the engine better, as over a
fixed number of operating hours, the number of times an oil molecule
is used to lubricate the parts is fewer and therefore it degrades
less.
Henry Nee
"heat capacitor" great analogy Henry.
Paul Lamar
If reducing oil level cured the over heat problem, it was probably a
product of oil foaming, and less oil could cure that. Foamed oil not
only reduces oil pressure, it cools the parts poorly and then gives
up less heat to the cooler. Rotaries foam the oil more than piston
engines and a synthetic racing oil with higher film strength and
more anti foaming agents are a help in that area.
If you see oil streaming down the side of the cowl and nearest is 25
miles. Would 5 quarts of oil be better than 7 quarts? Lynn E.
Hanover
Your up early Lynn :-)
You have to be careful when going on temperature alone. There are two
many variables. Time sitting on the ramp waiting to take off is just
one of many. A change in ambient temperature alone is a major change.
A one degree F ambient change is a one percent change in cooling.
When doing this kind of R&D you need a black box.
A $60 Maximite will record half a dozen temperatures and relate them
to the nearest real time second. It will also monitor the air
pressure on both sides of the oil cooler every second. It will store
32 gig of data on an SD card. Pull the SD card and read it with your
PC. That is probably several hours worth of data.
Here is the programming manual.
Paul Lamar
If the first scenario is true we are in real trouble with the 650HP
time to climb airplane. The dry sump oil tank is 5 gallons.
Paul Lamar
In my former street legal race car days, this was always a good
trick to keep oil temps down. Cooling tubes run through the oil pan.
The oil that is in the pan has excess heat removed by the air flow
through the tubes. If you use a spacer like I did with the stock
steel pan, it would be easy to weld these in.
[image: Inline image 1]
Kevin Alderman.
We tried that awhile ago. Very labor intensive to get enough tubes
in there to be effective. . It is better to just use an oil cooler
core as an oil pan. Here are some 3D's we did on that about ten years
ago.
The inline image did not work in Thunderbird Kevin and others. The
best way to submit images is attach them to your message.
Paul Lamar
Using an oil cooler core as an oil pan seems like a dandy idea. That’s
exactly what I want to do. I can still use an additional oil cooler heat
exchanger if needed for more cooling. What is the downside to this
approach and why is it not more popular? Thanks.
Gene Kahn
Not every one is bright enough to recognise a good idea when they see one.
Obviously present company excepted :-)
Paul Lamar
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