The Hot Oil Blues

[eschrom]

Hi Everyone,

I'm looking for advice from anyone running full flow with the cooler under the engine and getting good results. Can you describe your setup?

Mine is less than marginal. The idea is very simple: the cooler is in a shroud that ducts air from the smile, through the cooler and then overboard. There is no air flow over the rear part of the bottom of the case and I suspect that may be the problem but before I cut more holes in the shroud I'm curious about others' experience.

On Saturday the air temperature on the ground was mid 80s and in flight I had to hold the engine to 2500 rpm in order to keep the oil temperature from going above 215. Then I drilled some holes in my shroud to shoot air at the case and yesterday I could run the engine at 2700 but on the other hand the ambient was 10 degrees cooler than Saturday, soooo.... maybe yes, maybe no. The next step is to make bigger holes in the shroud unless someone can convince me to try something else.

Thanks in advance for any help.

Ed
2LS
GP 2276

 

[soneraifred]

Hi Ed:
This isn’t any help, but maybe a point of reference. I flew my IIL today for about 6 tenths of an hour. The OAT was in the mid to high 80’s. At cruise at 2500 ft, 25” MP, and around 3200 rpm, I was seeing oil temp in the neighborhood of 220 F. Mine is a top-mounted stock VW Type 1 cooler, with the oil temp probe in the side of the sump under cylinder #2 (RH rear).

 

[eschrom]

Thanks, Fred. How high a temperature are you comfortable with for a prolonged period? And what pressure do you see?

 

[soneraifred]

220 F is pushing my comfort level, although I have the gauge red lined at 250 F. The oil pressure was running about 55 psi. I have a 26mm oil pump with a pretty much standard oil system, although I don’t recall if the springs are stock. The oil is Shell Rotella T4 10W-30.

 

[tls258]

Ed-

Just a thought. Here is an instrument selling on Amazon for about $55 that measures airflow and temperature. Below is endoscope you can plug into phone, etc. to see what is happening, but you'd need something like tufts to watch the flow. Different cameras have different interface- I have one that is regular usb.

Idea here is that the anemometer can show you what kind of temperature and airflow you are getting in front of cooler. If you have another one in back of cooler, would give an idea how much flow is getting through cooler and how much heat the cooler is rejecting. More accurate oil temperature and flow would be in-line oil temp/flow probes.

The anemometer would help visualize air flow through the cowling. You could move it around to map the airflow and temps inside the cowling. If the ram air over the engine is higher pressure than your oil cooler ram air at the exit maybe it is causing back pressure to the oil cooler air. Maybe ducting path issue.

Air conditioner service has coil cleaner, like a dirt/degreaser if the fins (coil) are dirty. A little dirt goes a long way. If cooler is sized to reject enough heat and there is adequate airflow though the cooler, then air flow over engine case should not be a big factor since that is just more cooling surface.

MonkeyJack HT-9819 Digital LCD CFM/CMM Wind Speed Backlight Airflow Gauge Meter Thermo-Anemometer

Endoscope USB Microscopes Borescope incoSKY Inspection Snake Camera IP67 Waterproof for Android Smartphones and Windows PC (5M/16.4FT), TN2

Since oil temp is a primarily a function of retained combustion heat, here is a link to engine cooling ideas:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0ahUKEwihr-6--qzbAhXL1IMKHbBIBdcQFghIMAg&url=http%3A%2F%2Fx-jets.com%2FDesign_for_optimum_cooling_efficiency.pdf&usg=AOvVaw3hmiIwWGCdwrrkzjjAek6F

File link here is NASA study of engine cooling noting inlet and exit design importance. Has photos and schematics.
http://contrails.free.fr/fichiers2/miley_cooling_opposed.pdf

Here's link to jabi file that is more modern with good schematics of airflows in the cowl: http://www.jabiruna.com/wp-content/uploads/2015/03/Cooling_Flow_Tips.pdf

 

[tls258]

Another article on this topic:

"The exit is the key"
Cooling Drag by Christopher Zavatson, EAA 445507; from EAA Sport Aviation Magazine Dec 2007

In the Jabi article in previous post, note the exit lip which had big effect on cooling

 

[tls258]

Looked at the specs on those anemometers and max I saw was 113mph, and plastic, so would probably melt. Looking at the EAA article, maybe an air pressure gauge hooked up to a series of Piccolo tubes with line valves to select for the air pressures in various parts of the cowling would give a picture on air movement under the cowl. You could diagram that easily. A series of under-cowl air heat sensors could be selected to see heat flow through the cowling, after the cooler, etc. The oil temp and CHT show the temps in the engine but don't show what's going on with the air around the engine in real time, which is the issue. I think instrumenting under the cowl would be a way to gather the data.

The NASA article recommended on-ground testing with air generator. Tie the tail down? That would eliminate the risk of flying while trying to gather data and the data instruments could be outside the prop wash. You could make a little change and see the result quickly with a static run.

Ok, that's the end of my brain storm.

 

[smokyray]

Ed,
Living in Texas tends to educate one in the finer art of engine (and oil) cooling techniques. 8)
With 994SP, the original 2180 Scott installed had a full flow EMPI 56 row oil cooler mounted horizontally under the oil pan with a cooling entry hole below the prop on the lower cowl. He had documented cooling issues and was still working the issue when he left us.
I retained Scott's setup when I installed the "Ultimate 1835" however I utilized bigger, (#8) fire sleeved oil lines, a 24 Plate EMPI racing VW full flow oil cooler with improved mounting bracket/baffle, tighter cowl-cooler duct seal and close attention to detail sealing the aft cooler block baffling with High Temp RTV. When you turn air 90 degrees as in the aft cooler baffle, it needs to have a very tight seal and good cowl exit airflow to help it draw.

I also added 2 VG's to the lower cowl to excite the exit flow air, installed a plenum over the cylinders that came with the engine to lower CHT's and replaced all baffling new and insured it was sealed tight.
End Result:
Oil Temp@3100RPM 95F OAT 190-210F

Advice:
1. Check your oil temp sender for validity in boiling water (212F).
2. If not already equipped, install a remote oil cooler with #8 oil lines. (see link below)
3. Measure the cowl exit area. It should exceed your intake area by 1.5%. Seal any unneeded intake holes or leaks.


Oil cooler intake and VG's on 994SP
(Black square below oil cooler intake is original air intake which I sealed to increase cowl airflow)

V/R
Smokey

https://www.amazon.com/EMPI-00-9271-0-BUGGY-COOLER-PLATE/dp/B00BBJV4N6/ref=sr_1_24?s=automotive&ie=UTF8&qid=1527697098&sr=1-24&keywords=EMPI+vw+oil+coolers
48 row cooler on Amazon

 

[kennyw]

...I retained Scott's setup when I installed the "Ultimate 1835" however I utilized bigger, (#8) fire sleeved oil lines, a 24 Plate EMPI racing VW full flow oil cooler with improved mounting bracket/baffle, tighter cowl-cooler duct seal and close attention to detail sealing the aft cooler block baffling with High Temp RTV. When you turn air 90 degrees as in the aft cooler baffle, it needs to have a very tight seal and good cowl exit airflow to help it draw.

I also added 2 VG's to the lower cowl to excite the exit flow air, installed a plenum over the cylinders that came with the engine to lower CHT's and replaced all baffling new and insured it was sealed tight.
End Result:
Oil Temp@3100RPM 95F OAT 190-210F

I can attest to the efficacy of Smokyray's set up. This past winter, I had to block the cowl inlet for the oil cooler by 1/2 the width just to get oil temps into the green.

 

[eschrom]

Great stuff, fellas! Thanks to you all for your help.

Experimenting with anemometers sounds like a nice project (I'm an engineer) but right now I'm looking for a slam dunk. When I can fly it without one eye always on the OT gauge I'll start the lab work.

I have the cooler that's half as big as the one in the link and maybe that's the problem. If there is no easier solution I'll have to upgrade. Smokey Ray, in your photo I see the bottom of the case. Is all of it exposed to moving air? Any chance you could sketch a longitudinal section of the arrangement?

Thanks again, guys.

Ed

 

[smokyray]

Ed,
My crude hen scratching notwithstanding, here is my non-artists rendering of 994SP's setup.

There is a 2" gap between the cooler plenum bottom/oil cooler fins and sump fins. The plenum is fairly easy to fabricate out of .030. You can pop-rivet cowl chafe material to it to form a sealed inlet scoop that seals tight against the cowling.The 24 row EMPI racing cooler works very well on the 1835. The key is the cowl chafe material seal at the front and RTV around blocking plate at the back, has to be tight.

The plenum doesn't need to be as long as I fabricated, but I wanted it to be able to accept a 56 row cooler if needed. With the 24 row cooler there is a dead air space aft of the cooler prior to the blocking plate which circulates air over the sump fins. With a longer cooler, this space would be eliminated.



V/R
Smokey

 

[eschrom]

Well done! Thanks.

I'm not so sure about the aft half of the plenum being unnecessary. I have a hunch that air circulating over the bottom of the case is a significant contributor to oil cooling.

The red line in the first picture shows what I started with - a plenum that shoves air through the cooler and prohibits any from reaching the back of the case. Then I drilled some holes as shown in the second one and got a slight improvement (I think). The next step is to make the holes bigger. I'll post the result when I can but right now the weather forecast is hinting that it won't be this weekend.
Ed

 

[Bil4381]

I've had 2 oil coolers on my SII LS. The first was 7500 BTU for a 70 HP Jabiru 2200. It stayed around 210F and had a cowl Flap.
Presently I have a 15000 Oil cooler for the same SIILS cooling a Jabiru 3300 engine rated at 12o hp. I've been doing engine runs trying to sort out the takeoff RPM issues. I only got 2400 rpm. So I've purchased an aeroinjector based on the recommendation of a friend who runs on in his Sonex.
At 2400 rpm the oil temp has yet to move off the cold peg on the guage. The oil cooler adapter is thermostatically controlled. It should open at say 220F and close at 180F. I also have a cowl flap say 15" X 12" It open 8".
The oil cooler are is scooped into a sealed compartment below the oil pan, Forced upward through the oil cooler, then ducted aft all the way to the area just above the cowl flap.
Admittedly experience shows that what happens on ground runs is no indication of what happens in flight as the takeoff power and heat generation is continuous.
One choice might be to try a thicker oil cooler. IMHO it's critical to have a sealed oil cooler air path to bring cold air in and and duct it overboard after the oil cooler.
BillE

 

[eschrom]

Nice to hear from you, Bill. I've been wondering what happened with the J-3300. I hope to read a pirep soon.

Tightly ducted air flow is wonderful except that it's not doing enough for me. The more I think about it, my cooler probably is just too small but installing a bigger one will require some engineering and right now I'd rather fly. So I'll spray some more air on the bottom of the case and see what happens.

Ed

 

[Chucker]

FWIW,

Fred is running a 2180 and cooling it with a stock VW oil cooler. In the winter he even has to block airflow to the cooler to maintain minimum oil temperatures.

Bigger is not always the only and/or best answer.

 

[smokyray]

Amen brother!
I reached the same conclusion engineering cooling solutions on my Two RV's flying in FL and TX (not WI) heat. This experience helped immensely on 994SP.
Interestingly, the Sonerai cowling arrangement is nearly identical to the RV4 except smaller. Same concept, more efficient airflow through the cowl (and oil cooler), the cooler the oil (and engine).

Every installation is different, some need more cooling than others. It all boils down to experimentation, trial and error data and good collection and testing.

V/R
Smokey

 

[eschrom]

The solution turned out to be very simple - more air! I made both the smile opening and the cowl outlet bigger and voila! - nearly perfect oil temp. Today the OAT on the ground was upper 80s and even after a full power climb to 3000' AGL the oil never went above 205. At normal cruise it was maybe 190 and while loping along with a Cessna, 170. Life is good.

 

[Bil4381]

I now have a 18,000 btu cooler as the 15,000 leaked.
Bought an oil cooler thermostat from [email protected] at Sun and fun. I am expecting it to cycle open and closed and to see that in oil temperature.
The OC on my Deuce cycles all the time in flight, say from 80C to 110C. It has no thermostat. Lycoming 0-235-c1.
Bil438

 

[shocktrooper]

My 2074cc Great Plains engine has the top mounted AeroVee oil cooler with a very clever and nicely crafted (by previous owner(s) ram air box shrouding the front of the cooler body. It is fed cold ram air via a thumb sized duct and really short scat hose on each side of the box. The R & L ducts extend downward into the inlet air flow stream routing into the cylinder baffle boxes on each side.
It works great! So great in fact, that the previous owner stated he had to disconnect the feed hoses when flying "on really cold days".

 

[Bil4381]

Full power engine runs show 190F. Possibly it will cycle to 210F in flight. BTW the test flight is planned for today. 4 years work. Every day since Jan 2.
Should have good video. Two friend' are using my Deuce as chase plane. And video platform.
Bil438