My '93 ES300 has had a problem causing overheating in certain situations (long trips) About six months ago, I took the car in and the mechanicflushed the radiator and replaced the thermostat. The car has been working fine up until yesterday, when I took a trip up to a major metropolitan area on a hot day and had to pull over several times due to temp gauge shooting up. On shorter trip (up to 30 miles) the temperature does just fine. I'm going to take it in next week, but I was just wondering if there was anything I could check myself before doing so. Car has plenty of antifreeze and oil.