[prkaye]

Is there a preferred orientation of Vans' oil cooler (wrt which port is oil return and which is oil outlet)? I see no markings on the unit, and it appears to be physically symmetrical.

 

[zilik]

I don't think so

I don't think to cooler really cares which way the oil flows through it. Common practice is to put the inny is the bottom port and the outy the upper port. This way no air gets trapped in the cooler.

 

[prkaye]

Common practice is to put the inny is the bottom port and the outy the upper port.

OK, so it doesn't matter which port is up and which is down when i mount the cooler?

 

[scard]

Think about all the different orientations that people have mounted oil coolers; side-ways, angled a little this way, angled a lot that way, on the firewall, on the baffle... A lot of airplanes flying just fine for a lot of hours with oil coolers oriented every which way.

 

[Mel]

Everyone here is right.

The cooler doesn't care about direction of flow. Like Gary says, it's best to keep oil flowing "up-hill" to prevent air entrapment, but not a requirement.
Now, having said that, I'm talking about standard aircraft coolers. There are some aftermarket automotive coolers that call for flow in a particular direction, but they are seldom used on RVs.