In the wake of an NHSTA "formal safety investigation," GM today announced plans to add enhancements to the Chevy Volt's battery coolant system, in the hopes of preventing any post-crash electrical fires. As a result, some 8,000 Volt drivers will have to bring their cars back to their dealerships, as part of a move that's one notch below a formal recall. GM made the decision following federal investigation that saw three batteries erupt in flames after side-impact crash tests. Regulators blame…