Ive got a 99 Honda Prelude 150k miles fully stock - engine was replaced with another stock one.

So, when I come to stop lights it overheats but when Im driving it doesnt....

Fans DO NOT kick on UNLESS A/C is on , but I changed the fan relay 3 months ago ????

And sometimes, it doesnt overheat at stoplights , yesterday it did, today it chose not to.... WTF IS GOING ON !!!!!