Not my project - found this courtesy of Hack-a-Day.
This free and open source software tool is designed to make it easy for individuals to keep track of both the routine maintenance needs of their vehicles, as well as keep track of any previous or upcoming repairs and upgrades.
Demo here: https://demo.lubelogger.com/Login/Index
User/pass: test/1234
I think if you’re nerdy enough to self host stuff, you can definitely figure out LubeLogger. You don’t have to use all aspects of it… you can just use it for tracking gas mileage if you want.
If you want it to keep track of maintenance like oil changes and stuff, you have to add them manually and tell it how often you want them done.
For tracking gas mileage and maintenance reminders, all you need are 3 tabs - Service Records, Fuel, and Reminders. You can ignore everything else.