My sons 1990 Honda Accord has started running hot lately. I know very little about cars but do know that something is not right. When idling at a stop light temp gauge slowly rises to red mark. Also, we were on the highway coming home and temp rose again while driving. We pulled over and let cool. Checked radiator and added 50/50 to top off. (Outside temp has been in the low 100's) We continued back on road ran A/C and made it home safe. Today, drove car top work with no A/C on and temp went up again but then went back down.. it kept doing that whether it was idle or running... HELLLLPP.