Chapter 23 - Section 8

Oil Cooler


I spent hours and hours gathering information and pondering over my oil cooler mounting location. From all the information I gathered, there are three popular locations:

1) at the top center of firewall, right underneath the upper cowling (per plan);

2) by the wing root behind the strake;

3) below the engine forward of the alternator and starter (Plans do not recommend).


I heard successes and failures with all three installation locations. Makes you wonder what is the real recipe to make each of these locations work. I believe the two key elements are:

1) how well the engine baffles seal the incoming air from escaping and directing it to its intended exit route;

2) ensure a venting channel and low pressure port at the exit side of the oil cooler - that promotes good air flow through the fins of the oil cooler.       


My first preference was to place the oil cooler under the engine (3) because I do not have to cut a big hole on the cowling for exit air. I spent hours in evaluating the appropriate oil cooler for under the engine. I believe the Stuart Warner 8432R is the preferred cooler for that particular location. This oil cooler costs ~$650 and its small. I made a paper mock up and tried to fit it under my cowl. Surprisingly, I found limited to tight space for it. The one thing I do not like is the long hoses need for this mounting location. The Plans actually consider this not the most appropriate location for the oil cooler.


I decided to take a second look at the alternatives. Clark Canedy and Buly Aliev both had success with the firewall mounting location per Plan. I happen to have the same engine as Clark. After multiple discussions with both and others, I decided to mount my oil cooler as they did and per Plan. Is this a good decision? I dunno... I'll report back after my first flight.


Oil Cooler Decision

Based on Cozy builder consensus, it is easier to deal with too much cooling than not enough cooling. Since my firewall mounting location is spacious enough to accommodate a 17-row cooler (same as Clark's), I decided to get the same - Aero-Class PN# 08-00644 ~$340. Besides, it is certainly much cheaper than the Stuart Warner equivalent.


I pretty much followed the Plan's mounting method and made a set of mounting brackets. Keith Spreurer's EAA workshop happens to have a wider sheet metal brake. So I pre-cut the sheet metal and bent them at his shop. Once bent, I brought them back and mounted them on the bench - to make sure I got a balanced 10o angle per Plan. 





Here's a picture with the oil cooler mounted at the fire wall.











Cooler Vent

As discussed above, the cooler vent is an important component to promote good air flow from the pressurized cowling to the outside. Since the top cowl is curved, the cooler vent must conformed. I doubled sided a 2" soft foam block on top of the oil cooler and shaped the top of the foam with the straight edge sanding block. 


Though it is hard to see from my picture, I added an 1/8" thick aluminum plate under the foam block. This will be used as a flow control plate - in the event I have too much "cool". I picked the idea up from Tim Andres' set up. He drilled several large holes on the plate and mounted it on top of the oil cooler when he has too much cooling during the winter months. I also shaved the foam down a bit to accommodate the thickness of the cowling and the 'oil cooler screen' discussed below.




Once I was happy with the foam block, I moved the oil cooler and foam onto the work bench for glassing. I laid up 3 layers of BID and made my initial oil cooler vent. I soon realized all the shaping with the foam was not really necessary because it was almost impossible to make a good layup with a single pass.


I ended up making two passes in glassing the oil cooler vent. This is the 1st pass. After the glass cured, I trimmed the glass at the top to the foam level. Then I removed the foam and remounted the entire assembly to the fire wall for glassing the upper half of the vent.






Then, I realized I needed to mark and cut the exit hole at the cowling first. Otherwise the upper half of the vent will block off the vent opening for marking onto the cowling. Note I used masking tape to mark the hole location because there's such a tight space, I have difficulty in sticking a pen in.









I am always apprehensive in cutting a big hole on any part of the plane. Nonetheless, I charged forward. I started with a 1" hole saw at all 4 corners. Then I connected them up with my FEIN tool and straight edge sanding block.










Some how, I needed to cover up this big hole. I borrowed another idea from Buly and picked up a metal mesh screen file holder from Staples. I ground off its metal frame and used the screen material (sheet) as a cover. At least to keep larger debris out of the oil cooler fins. I trimmed the screen to shape and sandwiched all 4 edges with flox and BID - forming a picture frame (2 BID on each side + flox between the screen material). The reason I added flox is to provide added stiffness to the screen - conforming to the curvature of the cowl. The masking tape was there for alignment during the glassing process.







Here's a picture of the screen after it was completed. Since the upper cowl is not that thick, the screen looked flush without additional effort.











Per Plan, an optional deflector can be added ahead of the oil cooler vent to create a low pressure zone at the oil cooler vent exit. This will help to draw the higher pressure air inside the cowl to escape through the vent. I decided to add the deflector at this time. As all Cozy builder know, it is easier to deal with too much cooling than not enough.


The spacing in front of the oil cooler hole is relatively limited (~1" wide) and I cannot find any recommended dimension for the deflector. After chatter with other Cozy builders, I decided to make my deflector 1" x 1/2" x 7.5". That will give me a slope of 34o. I used a strip of scrap blue foam and cut it to shape with my band saw. Then I flox the foam strip onto the cowling. After the flox cures, I glassed the forward face of the deflector with 3 BID. After it cures, I trim the excess BID, carved out the blue foam around the edges (for flox corners) and glassed the back side with 4 BID - just figure it going to be warmer of that side.   


Note that I also added 4 nut plates on the flanges of the oil cooler vent. The four (4) AN-3 bolts are there to connect up the upper cowling, through the screen to the vent. Providing a tight seal.