Which passenger car has the biggest gas tank for diesel?

There isn't a single definitive answer to which passenger car has the largest diesel fuel tank. The size of a fuel tank can vary even within the same model year and trim level depending on the region and specific options. Also, manufacturers don't always publicly list this specification prominently.

To find the car with the largest diesel tank, you'd need to research current model year specifications for large SUVs and trucks from manufacturers known for diesel options (like Ram, Ford, Chevrolet, and others, and possibly some European manufacturers) and compare their fuel tank capacities. Even then, a new model could come out tomorrow with a larger tank.