Oil purge

First of all, you do not need to purge on every oil change if you do things properly. I have never purged after my first time when the engine was first started.

2nd, a new o-ring is only needed if the old one is leaking. Carefully reuse the old one and run the engine. It will be easy to see if there is any leakage/weepage on the bottom edge of the valve cover; if there is, replace the o-ring. I don't recommend this practice if the o-ring is internal and leakage can't be readily observed or if its very difficult to replace.

Thanks. I just put a new (larger) oil cooler in and a thermostat.  I didn’t fill the oil cooler before attaching all the hoses and it could prove difficult to remove them to do so. Will the oil cooler fill ok if I spin the prop enough?

The oil cooler will fill just fine by spinning the prop.

The thermostat is NOT an All or Nothing device.

When the engine is cold the thermostat is Open and allows Oil to bypass the Oil cooler but some oil is still passing through the cooler.

When the thermostat closes, all the oil passes through the cooler.

Once you see Oil pressure by turning the prop, the hoses are filled and the pump is primed.

Start the engine and monitor the oil pressure.

You should see 15+ psi within 5 seconds and then it may fluctuate for the next 10-30 seconds.

Within a minute, the complete volume of Oil (4L) has passed through the engine at least once and any air is now gone.

Will it get any air at the very top out do you think. Above the outlet hose. (Seepic)

The picture didn't attach.

As long as the OUT connection is on the top, or is the upper connection if on the side, the cooler will fill completely.

There may be cooling fins above the connection but I doubt the design has any Oil chamber above the connection.