My beloved Saab 900 is overheating

[steiraug]

hello, i am new to the forum, i just got a nice Saab 1987 a month ago and in the past week i noticed that the gauge is close to the red mark ,it does overheat especially in traffic stop and go , i checked the extension coolant tank and it is full, the hoses are very very hot, when i get home the fans keeps running for like 3 minutes then stop, i asked the guy who sold it to me if it overheats, he told me it did at one point and it was the thermostat , and he replaced it. i did not notice any coolant leak..the amount in the tank stays the same. any help would be greatly appreciated, i will be devastated if i blow the head.