Server RAM space filling up and load average increasing

I have a site egully.com
The server configurations are Xeon-2 processor (Quad Core) , 8GB RAM.
I am facing the following problem; Normally the average load remains in the region of 1-3% and the RAM usage is between 2-4GB
Sometimes the RAM space gets filled up and because of lack of space the other connections in queue goes in loop. This is where the problem starts ; the RAM doesn't get empty and the requests keeps on increasing. The load average shoots upto 25-30 and the system goes down.
The system only revives once we restart "apache". I have observed that the RAM is clogged by some temp files and also lot of httpd files (Apache) and once we restart apache all files are gone and system comes back to normal. Everything works fine till another such high load cycle comes again.

Is there any way by which the files in the RAM can be auto deleted once it reaches certain size or if the load average reaches certain value. Any kind of suggestion will be highly appreciable

My my.cnf settings are as follows :

[mysqld]
datadir = /var/lib/mysql/
tmpdir = /var/tmp/

bind-address = 127.0.0.1
max_connections=200
key_buffer_size=768M
table_cache=256

join_buffer_size=1M
read_buffer_size=1M
sort_buffer_size=4M
tmp_table_size=4M
read_rnd_buffer_size=1M
max_heap_table_size=4M
#myisam_sort_buffer_size=128M
thread_cache_size=4
#thread_cache=32
#query_cache_type=1
query_cache_limit=3M
query_cache_size=8M
thread_concurrency=8
wait_timeout = 10
connect_timeout = 10
interactive_timeout = 10
long_query_time=1
#max_allowed_packet=128M
skip-bdb
#innodb_buffer_pool_size=1024M
innodb_file_per_table = 1

#innodb_additional_mem_pool_size=20M

# Set the log file size to about 25% of the buffer pool size
#innodb_log_file_size=256M
#innodb_log_buffer_size=8M

#innodb_flush_log_at_trx_commit=1
#innodb_lock_wait_timeout=60
log_slow_queries = /var/lib/mysql/slow_log

[isamchk]
#key_buffer = 16M
#sort_buffer_size = 1M
#read_buffer = 1M
#write_buffer = 1M

[myisamchk]
#key_buffer = 16M
#sort_buffer_size = 1M
#read_buffer = 1M
#write_buffer = 1M

[mysqlhotcopy]
interactive-timeout