I have a 92' Jeep wrangler. Just recently, there has been a loud noise coming from under my hood followed by a back fire when changing from 2nd to 3rd gear. I noticed the exhaust manifolds bolts and the head gaskets bolts were loose. I tightened both the manifold and head and the noise is still there. Just to top it off, my temp guage now is rising. I have already replaced the thermostat...... Any ideas?