There's a larger elephant in the room that everyone is forgetting here: The diesel cycle's effect on the cylinder liners
The reason why traditional coolants are not good for diesel engines is because of cylinder liner pitting and cavitation. Every time a diesel's cylinder undergoes a power stroke, the coolant around the cylinder liner erupts with tiny air bubbles that eat the cylinder liner, as cavitation does to metals.
A heavy duty coolant meant for diesel engines has additives that prevent this from happening.
PFCG and Rotella ELC are perfectly acceptable for your engine.
If I were you, I would just do the total flush and convert over to an appropriate coolant.
The reason why traditional coolants are not good for diesel engines is because of cylinder liner pitting and cavitation. Every time a diesel's cylinder undergoes a power stroke, the coolant around the cylinder liner erupts with tiny air bubbles that eat the cylinder liner, as cavitation does to metals.
A heavy duty coolant meant for diesel engines has additives that prevent this from happening.
PFCG and Rotella ELC are perfectly acceptable for your engine.
If I were you, I would just do the total flush and convert over to an appropriate coolant.