There’s not a single factor that made this engine a disaster, but some of the problems loom larger than the others. Perhaps the biggest issue was it was a converted gasoline engine that used a lot of the same design, so the higher compression ratio with diesel led to all sorts of issues. Using the same head bolts proved to be a huge oversight, as they stretched out and broke, and that led into head-gasket problems. From there, coolant leaked into the engine cylinders and led to failure.
The underappreciated Monte Carlo suffered as a result of this botched engine, and sales declined throughout the 1980s as a result. Even when GM moved away from the V8 diesel and replaced it with a V6, sales of the Monte Carlo struggled to bounce back. Production ended for the line as a whole in 1988 before eventually returning for the 1995 model year with a 3.1L or 3.4L V6 engine depending on the trim.
