I have a lovely collapsible literature display that contains all the mods done on my car. I used to show it a TON, so it lived in my trunk. It’s been retired from the car show scene for many years on account of me having a kid and the paint flaking off, but the display still remains in my trunk.
But as far as a “golden book,” I also keep a 6 inch thick folder in my trunk that contains absolutely everything. There’s an inspection section, registration section, tire section, history, v8 swap, receipts from the 90s, 00s, and 10s. I even have a speeding ticket the previous owner got in 95.
Keeping all these documents has come in handy. Typically in regards to parts that have a lifetime warranty. Store and manufacturers don’t expect someone will actually keep a receipt that old, which is many times, a requirement. I can’t tell you how many window motors I’ve gone through!
I remember in 2009 needing a tune. The company wouldn’t give me a copy, even though I brought a flash drive. They claimed they keep everything stored in the event that anyone needed a retune. I showed up 9 years later with a print out of the dyno they ran (straight out of my folder), and reminded them of the file they saved. Well, after a relocation, computer and software upgrades, they naturally couldn’t find the archived file and had to retuned the car from scratch.
I’ve also got a mileage spreadsheet on the cloud where I calculate fuel economy, price of gas, etc, and printed out several pages in there. Being able to see why and where fuel economy plummets is pretty useful.
But mostly whenever you are troubleshooting it helps to have that folder. When you’ve had your AC working occasionally, and you can go back and see what all was replaced several years back, you can determine from there where to go. A real shop would fix and recharge, only to send you off with a working AC, that only lasts a year. You return next summer, then what? They might not be able to look up what they did, and charge you the exact same service as before.
