There are coolers that are an
S
S
pipe with cooling fins,
and there are coolers that are
II======II
II======II
II======II
II...........II
2 in/outlets into a finned cavity.
With the continuous S pipe design, the air would be pushed straight through, but with the other form, mounted with the pipes at the bottom, I can't see how ther air could possibly be bled, just compressed into a smaller pocket at the top when under pressure.
Household central heating radiators are fitted in this way, and to remove the air lock, need bleeding from a valve at the top.
Unless the exit pipe extends inside the cooler to the top, how could an oil cooler be without the same physics?