Oil Cooler Orientation

[skippydiesel]

Most  Rotax 9 oil coolers seem to be mounted, with the in/out ports at the top, oriented across to the aircraft longitudinal axis and almost vertical (allowing for cowling shape) at the front of the engine compartment. This often results in long contorted hose runs and when new / replacing hose, the potential for air to remain trapped within the system, much reducing its cooling efficiency.

 

My Zephyr had the cooler almost flat, slight upward tilt on the inward side, mounted low, on the right (aircraft) side of the firewall, in/out ports facing forward. It worked very well.

 

I plan to have my Sonex/Rotax 912 ULS oil cooler mounted below the crank case, between the two front exhaust pipes.

 

Version 1. It would look as per my first sentence (quite conventional), however this brings the sides of the cooler quite close to the exhaust pipes. For my piece of mind I would fit some form of heat shielding. Future (5 year) servicing may be a tad fiddly, with  access being tight.  The hose runs would be quite long and curved, increasing the potential for the hose to collapse when hot. Then there is the usual concern about air trapped in the system and the need for much "purging" to ensure a completely oil filled system.

 

Version 2. The alternative would be to rotate the cooler 90 degrees. (Imagine holding the cooler at arms length, in/out ports at the top , now rotate the cooler 90 degrees, to your left, so that ports are on one side) Still located between the two exhaust pipes, now with much greater clearances all round.  In/out ports would be on the aircraft right side, with a definite upper/lower port. The side ports,appear to facilitate almost straight hose routing,  with shorter runs/lengths. "Purging" the system of air would be straight forward with little chance of air entrapment.

 

 I can see no down side to Version 2  (can you?)

[scsirob]

I'm using your Version 2 on my CAMit engine install. Works a treat, most of the year I have to block a large portion of the cooler to get the oil over 80 degrees C.

Thinking about exchanging for a smaller cooler.

 

[skippydiesel]

Wow! thatch one very nice looking set up. What brand/size cooler is that?

[cscotthendry]

With version 2, if the cooler is above the level of the tank, the oil can drain out of the cooler and create an air pocket in the oil system that has to be purged by the oil pump every time the engine is started. Since the cooler is usually on the suction side of the oil system, this could introduce air into the lifters and possibly cause a valve strike.
This is why oil coolers are almost always mounted with the connections facing up and why rotax advise not draining the cooler during oil changes and why they have that involved method for purging air out of the system if you do completely drain all the oil.

[scsirob]

7 minutes ago, skippydiesel said:

Wow! thatch one very nice looking set up. What brand/size cooler is that?

Thanks! I built a plenum around the sump so the air passes along the sump and through the oil cooler, then down and out through the bottom of the cowl. That way it doesn't upset the low pressure needed for head cooling too much. Got two 3-into-1 CAMit mufflers, so there's ample space.

 

The cooler is a universal type, I got it from a local VW hotrod shop: https://www.hotrod.nl/shop/contents/nl/p3271_Oliekoeler_element_48_rijen_____280_x_190_x_40_mm_.html

I've seen similar ones in webshops around the world. In retrospect I should have gotten one size smaller, perhaps I'll swap it out later this year.