I do exactly the same - logged everything into Excel, pretty simple: Date, Mileage, work done, and who work was done by. I added in the spotty records from before I owned the car too.

I don't keep a mpg as my odometer sometimes stops working for a few dozen miles & then starts again, plus my speedometer is about 4 mph fast. Someday I'll fix those things, but....the one thing I'm really bad about is procrastination, and no computer program has been able to help me with that yet.

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1976 240D "Katja"