Infiniti: 04 g35x

infiniti just replaced my short block motor. The heating system now isn;t
working properly. When I am at ideal the heat is cold but as I spead up
the heat warms but never gets hot!Infiniti has had it for 2 full days and
are now telling me that it is air in the heating system! does this make
sence?

yes it does make sence. when there is air in the heating system a little
amount of water will be allowed in it. so you might want to bleed all the
air out of it.