Always prime before installing but, the engine will drain out a lot and the cooler will be dry usually at this point.

During a dry (NO Fuel) startup the amount of cranking can really take its toll on the starter and batteries.

With the plugs removed the engine spins at twice or more RPM and does so easily.

The entire spin up and bleed out should take only a few minutes.

(other than replacing the plugs)

Just an easy way to do it.

Robyn