Mark, how much space do you have between rad & fan with the G35? I have a 52mm 3 core rad and my G35 fan only has 15 mm space at the bottom. I moved the rad top further forward to have a bit more there.
I also put 3 x 18ml into my hub but it's never been hot enough to lock it.

Edit: forgot to add I use a 77 degree Tridon thermostat.