Linux diskspace usage

when /var directory of my machine gets filled up (85%) i removed some old logs. but after cleaning df -k command still shows that /var is still 85% full.

It can detect the actual disk space only after I restart the machine. Is there a way to force df to reflect actual free space without rebooting? My machine is a production one and can't afford down time. My OS is Red Hat 6.2
Thanks!

du -h /var will get you what you need.