Engine Cooling Plenum

Cooling Plenum

Here are some pics of the aluminum plenum I designed for my O-360 RV-6. The sides are built from the standard Van's baffle kit, and the top lid is my own creation.

I am very happy with the results. Highest CHT (usually #2) is around 385, the rest are 360-375, at 65% cruise, OAT in the 70s to lower 80s. Haven't had a chance to try it on a really hot day yet. Highest CHT in extended climb (also #2) is around 410. Oil temps are in the mid 180s. Before I put the small piece on the cooler to partially block air, the highest I could get was 175, with 80 deg. OAT. I did recently pull the temp sender and calibrate it again with boiling water, and it is dead on.

The outer portions are attached with hinges, so the top plugs can be accessed without taking the whole deal apart. The only problem I have had is a little bit of fretting of the hinge pins. I am experimenting with replacing the hinge pins with drill bit stock which is a tighter fit. No cracks of any kind, and I keep an especially close eye on the area around the oil cooler. I have about 80 hours on the installation.

Since first published these photos before Oshkosh 2004, I've had about a zillion questions about the plenum. At Oshkosh, and more recently at Land of Enchantment '04 I had the cowl off, and have had another zillion more. To answer the most common ones:

-No I did not draw up any plans (wish now that I had. At $5 apiece I would already have

my Harmon Rocket paid for.)

-No I do not have any specific dimensions. I started with the basic Van's baffle kit and

eyeball engineered it from there.

-Yes I know that the inlet looks like a pretty sharp transition. I'm sure it is less efficient than

a nice, rounded fiberglass plenum. The proof, however, is in the pudding, as it cools quite

well. I plan to experiment with rounding off the transition to see if it gets any better. When I

do get around to it I will post the results here.

Update: I now have about 130 hours on the installation. I ended up replacing the standard hinge pin with some #29AWG drill rod stock. The stock had to be sanded down just a bit, and had to be oiled up and forced into the hinges with a drill motor. It was a very, very tight fit. The result has been no more fretting by the stock hinge pin vibrating around in the hinges. A very recommended modification.

Furthermore, with Wisconsin winter upon us, and daily high temps in the single digits ºF, I am finding that the engine cools a little too well. See the Winter Cooling Mods link for details on the fixes for this.

Update 1-13-05: There has been some discussion recently about the oil cooler flanges cracking where the aluminum spacers meet the cooler. Dan Checkoway brought this to everyone's attention after experiencing cracks. I took a close look at my installation after this. No cracks so far, but that doesn't mean it won't crack in the future. The above photo is the way the plans call for it to be done. I added some reinforcement to the inner part of the flanges where the spacers meet the flanges. Hopefully this will distribute the load more evenly and prevent cracking.