Rot Gut Engine Upgrade
The Rot Gut Engine Upgrade is an upgrade option available from T-Ray that allows you to fuel your vehicle not only with SEC and MFC, but alternately with Rot Gut too! When standard fuel options are limited, it's convenient to have this fuel option as Rot Gut can easily be made with Fruit, Wood, and a Still.
To get the upgrade, you might not need to park the car at the garage in New Reno. If you do park there, don't expect your car to appear inside the garage itself. T-Ray should do the upgrade anyway, and likely only needs the vehicle's Key.