Oil cooling Full Circle

I thought I'd share my experiences encounter while going through the process of relocating my oil cooler. Hopefully this will be usefull to others either thinking of doing it, or for those who actually need to.
Some basic information first. I completed my 7A in November of 2011. It has an XIO-360 set up with Van's standard 7 row oil cooler. At the time of completion the cooler was mounted in the stardard location behind number 4. My cyclinder temps have always been fine and the original oil temps were about 185. One thing to take into consideration is that early flights were done in the California winter, so temps were probably around 55 or so. In May of 2012 I decided to move my oil cooler to the left side of the lower cowl to test a 4 inch NACA scoop. Here's some pics of the install.







The incoming air flow originally just dumped into the engine compartment. When I tested this setup it was now summer time and OATs were probably around 75 to 85. Cyclinder temps continued to remain fine. A little higher I think, but my oil temps would slowly climb to the 220s when ran WOT for say 5 minutes. Being that it was now summer, with higher temps, I wasn't too sure if the higher oil temps were due to that, or if the intake air was restricted because it dumped into the engine compartment. This could be the cause of slightly higher cycinder temps as well. Too much air in, not enough getting out.
So I then decide to try and channel the oil cooler exhaust in a way that would isolate it from the engine compartment. I also wanted to perform the first tests under the same winter temps in hope of achieving my original oil temps around 180.
Here's what I came up with. I made a fiberglass duct that would seal around the exit side of the oil cooler and the fire wall forming air path down to the lower cowl. From there, a 3 inch silicone hose with a 45 degree bend would channel the exit flow into an airbox and finally out through a lower cowl vent.



Sorry it's not rotated.

One thing I want to add. Right before starting the rechanneling mods in December I flew it WOT in cold temps and the oil temps still slowly climbed to the 220s.
This morning I made the first test flight with all cooler exhaust air exiting a lower cowl vent. OAT was about 53F and oil temps never saw anything above 180 and I was pushing it. For the moment things look really good but I'll keep you posted as more time is flown off.

OIl Cooler results

That really should get great air flow thru the cooler. Just curious if you 're using some additional data points for getting oil Temp in and oil temp out of the cooler without the effects of the vernatherm or bypass devise in the accessory case? I would think that arrangement would get maximum cooling effects with the possibility of having to close off the air side to get the temp up to set point.

Unfortunately I'm not the type of person who likes to get crazy with data, if I don't have too. I'm usually happy with "yes" it does work, or "no" it doesn't. I think in extreme cold areas this setup may in fact need to be controlled. I'm just going to insert a large wiffle ball in the NACA if need be. My flying probably won't ever require that though.

Pressure differential drives the cooling mass through the system. Perhaps you might quantify the system, starting with the inlet and working your way through to the exit in a logical manner. Does the side inlet equal or exceed the pressure of the standard upper plenum source, as measured at the oil cooler face? If not, the place to start is the inlet shape and/or location.

OIl Cooler

Heat exchangers can be difficult to troubleshoot. They have a lot of "hidden variables". But for sure the temp differential X mass flow in from the air side has got to equal the mass flow of the oil x temp differential out. Can't fool mother nature. Relocating can sure change the variables.

From recent experience

I am no expert in oil cooling set ups but like you, I can see when it works and when it does not.
A hangar neigbor with a tighly cowled Glassair II decided to reroute a perfectly good oil cooler set up. The set up was taking plenum air behind Cyl4 and dumping hot air out the side of the cowl via a 4"x4" set of louvers, never had trouble keeping the oil temps under control in his 200 hp IO-360.
At 400 hours Cyl 4 developed a crack and the oil cooler set up, robbing air, was blamed.
A NACA was installed much like yours in place of the louvers and air dumped out the bottom. This set up has overheated his oil temps on every subsequent flight and finally has been reinstalled the way it worked before.
My guess is that pressure on the side of the cowl is lower than pressure on the bottom of the cowl and maybe even lower than inside the cowl.
I suppose you could measure the pressures as Dan pointed out and find if you even have a pressure differential or perhaps a negative flow backwards.
Either way having oil temps climb to 220 F seems a lot like an oil cooler that does not cool at all. Hope you find a good solution.

Chris NACA inlets are not good for pressure recovery. I think you have found that the pressure in your cowl is lower near the outlet. As Dan posted delta P is what drives cooler efficiency. You may also have lowered the pressure a bit with the outlet duct you installed to direct the air. Can't know for sure without a diff pressure measurement. You could try removing the hose and seeing what results you get, just for fun.

Confused?

I think there's some confusion. The oil temps climbed to 220 when I just had the NACA dumping into the engine compartment. The most recent mod was channeling this air out the bottom of the cowl. From my first test flight today it appears that this modification has returned the oil temps back what they were when the cooler was mounted behind number 4.

My experiments with NACA inlet at the lower cowl helped improve overall cooling but not for reason I expected.

At one point the inlets were duct taped shut to test their effect on cooling. Not much change noted. But what was noted was one inlet had no tape, it had been blown off by internal pressure.

I believe more air exits than enters with NACA cowl vents.

I also have a NASA duct feeding my oil cooler in the same basic location. Mine dumps into the engine bay. I have taken lots of delta P readings with this set-up, and will post that information and photos when I have a little more time. - I am seeing 220 in the summer, and 165 in the winter. My plan was to duct the oil cooler exhaust out the bottom, but my delta P data suggested that it may not help. of course, the delta P in that location will change once the oil cooler exhaust is no longer compeating with the ram air. - I usually see 290 on the cylinder heads. - By the way, this is with an O-360, FP and a Sam James Cow.

Cfrisella said:

I think there's some confusion. The oil temps climbed to 220 when I just had the NACA dumping into the engine compartment. The most recent mod was channeling this air out the bottom of the cowl. From my first test flight today it appears that this modification has returned the oil temps back what they were when the cooler was mounted behind number 4.

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I suspect the current inlet shape and placement results in less pressure at the cooler face than the typical rear baffle or ducted-from-the-baffle arrangement (which is typically 60 to 90% of available dynamic pressure). The only way to know is measurement.

CFD plots suggest the side of the cowl is a low pressure area as compared to a more pitot-like location.

Detail design can be a factor. In my humble understanding, flow separation is the major issue in ducts intended for dynamic pressure recovery. The sharp turns at the two marked locations may be worth review:



Routing a cooler exit duct to the cowl exit would result in more pressure differential across the cooler. Pressure inside the lower cowl is higher than just aft of the cowl exit.

There are two ways to skin the cat (same mass flow across the cooler)...high pressure at the cooler face dumping into an area of moderate pressure, or moderate pressure at the cooler face dumping into an area of low pressure. Right now I think you're doing the latter. Nothing wrong with it. Does it offer some advantage?

I have a very similar setup on my 7A. I was not getting the results I had hoped for and enlarged the NACA opening with no effect, then added a helper scoop to the back side of the NACA, still with no effect. Finally, I measured the differential pressure with a Magnahelic pressure gauge. I was only getting around 3.4" to 4". Out of frustration I decided to make sure my seal to the cowl bottom was not leaking, so I used duct tape to seal the exit plenum. Differential pressure jumped to 6". I have found that anything above 6" seems to make things work OK..

The seal I had made appeared to be a good seal but the duct tape proved it was not. This showed that it only takes a tiny amount of air leakage to allow the cowl pressure to equalize into the exit plenum thus destroying the differential that makes the thing work.

Measuring earlier in the game would have saved alot of work.

I've re read the original post and still can't find if there was a "problem" with the original setup... Was this just an experiment to see what happens?

I'll agree that the basic premise of cutting a large hole in the baffle behind #4 to feed the oil cooler seems counterproductive, it does work fairly well. And the good news is this basic configuration can be improved dramatically with a few detail changes. I have a small plenum behind the baffle on #4 which is fed by a small slot at the top (above the fins) in the otherwise solid baffle. Now, the oil cooler is not "stealing" air from #4, but is still in essentially the same location. This mod resulted in a reduction in both CHT and OT. In fact, #4 became my coolest, and I have never seen more than 210 degrees OT (normal cruise is ~185 in summer).

And BTW, is the cooler hanging from flat stock with the new setup? Hard to tell from the pictures, but if so, I would expect that to fail in fairly short order. Better keep an eye on it, and possibly have some repair supplies with you at all times to get you home until the design is proven.

It's mounted on angled stock the same it was mounted on the baffles. Then to the motor mount via four clamps. I can see a clamp breaking, but time will tell.

plenum behind the baffle on #4.

Toobuilder said:

I have a small plenum behind the baffle on #4 which is fed by a small slot at the top (above the fins) in the otherwise solid baffle. Now, the oil cooler is not "stealing" air from #4, but is still in essentially the same location. This mod resulted in a reduction in both CHT and OT. In fact, #4 became my coolest, and I have never seen more than 210 degrees OT (normal cruise is ~185 in summer).

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Do you have some pictures of your setup that you can post?

Mark33 said:

Do you have some pictures of your setup that you can post?

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New thread started with pictures