When it seems as though nothing you are doing is keeping your servers cooled down when they are under a heavy load, you need to start examining your alternatives. You should start by looking at your rack design to ensure that your servers are getting the cooling air flow that they need. If this is not the problem, you might want to consider adding one or more rack mount fans to the system.
Rack Mount Fans Add Significant Cooling Air Flow
When you add one or more rack mount fans to your server racks, you will be able to increase the flow of cooling air in the rack significantly. This can mean the difference between keeping your servers cooling and running at optimum performance or losing them to overheating due to the lack of the necessary cooling air flow, which can be very expensive.