The Jeep 4.0L inline-six was the last true Jeep/AMC engine design before Chrysler bought everything and folded it into the Pentastar family. It was the final derivative of the old 4.2 inline-six and debuted in the 1987 model year. It’s last year in an American Jeep would be 2006, when the TJ Wrangler ended production. But you’re not here for a history lesson, so for the complete background on the 4.0L click HERE.
What does this have to do with heat?
The 4.0L is a massive hunk of cast iron American greatness. But all that cast iron means it’s a giant heat source under the hood, and once it gets hot it holds that heat for a while. And everything around it underhood soaks up all that heat, which can negatively affect performance, reliability, and component life. But with some application of Heatshield Products thermal barriers, the amo