Folks--

I have a bit of a clearance problem for my oil cooler. As is usual, I
can either mount it where it gets good air flow or I can mount it
where fits nicely--but of course, not both.

I am opting for the good air flow for all the obvious reasons. Part
of what makes this location tricky is the necessity of mounting the
cooler upside-down, i.e. with the fittings facing down rather than on
top.

As I was working this out, I became quite concerned that the cooler
would air lock, since the cooler sits above the engine and the
breather port. In other words, the cooler is the high point in the
oil system and if the fittings are on the bottom, I worry that any air
previously present in the cooler or air that becomes introduced into
it will stay in the cooler and displace a volume of oil.

Now I am not a "wrench" so I bounced this concern off of everyone I
could find, including the engine dealer, several other homebuilders
and some knowledgeable race car guys. Out of approximately 8 guys, 7
told me it was not a problem (the dealer among them) and only 1 shared
my air locking concern.

The No Problem 7 all told me that the normal operating oil pressure
would purge the air from the cooler. Now I like this because it gets
me off the hook, but I can't visualize it. I'm an old SCUBA guy, and
in that realm we always see bubbles compress down until they are
equalized with the ambient pressure, but they never, never, never
purge.

When I voiced that counter-concern, the engine guys all said that the
analogy is not valid because the oil is so much more viscous than
water. Yes it is, but I can't get my head around how that makes the
air purge any differently.

So I am putting this out to a broader audience--what are your thoughts
or observations on mounting an oil cooler upside down? Bonus points
to anyone who has actually done it.

Thanks--

Steve.