My uncle has a 1998 Jeep Grand Cherokee with the 4.0 I6. I'm not sure how many miles, probably around 180k. He said it recently developed a loud tapping noise, like it's in the valvetrain. He took it to his mechanic who tried to tighten up the rockers, but he said it's somewhere deeper in the engine. My uncle doesn't want to tear into the engine to fix it. He's decided to just run it till it blows. But in the meantime, he'd like to just quiet the noise. He knows additives aren't going to actually fix the problem. He knows it's going to blow sooner or later. He just doesn't want to hear the noise right now. Should he just use a thicker oil, or are there any additives you'd recommend?