问:1999年旁蒂克大艾姆粗糙和气味奇怪的运行

我把我的1999旁蒂克大艾姆v6机械由于过热。之前他在这汽车跑好但过热。有时透支温度计。它也有冷却剂泄漏。他取代了摄入垫片,它不再泄漏,但现在运行得非常粗糙和不稳定。我的头反射的座位摇那么糟糕。它有一个奇怪的气味来自排气。我不能很清楚的解释它闻起来像(可能与冷却剂?)它似乎没有过热,一滴不漏了。但蛇形皮带是分解。也许他没有把它放在对吧? I just hope my car isn't screwed. it can still hit 70 mph just fine though, while it's in motion at 60 mph I don't really notice it anything, it doesn't show any signs of dying, just rough running, shredding belt, and odd smell coming from exhaust. I just want to know what's wrong with it or if it's safe to drive if I replace the belt

我的车有170000英里。
我的车有一个自动变速器。