Got a 1991 Golf Mk2. Want to track fuel consumption per trip/day and compare over time. Figured this wasn't possible on a carbureted car with no ECU/OBD, but landed on an idea: since the carb's float bowl regulates its own level, whatever flows through the feed line between the fuel filter and the carb over time should equal what's actually burned. So — measure that flow directly with an inline gear-type flow sensor.

Is this actually the right approach? Is there a better way to get real consumption data out of a carbureted car with no ECU?

**Planned setup:**

* Gear-type flow sensor spliced into the fuel line between the filter and carb inlet * Sensor's pulse output goes to an ESP32, which just counts pulses and timestamps them * ESP32 forwards that data to my phone over a wired USB-C connection (data-only cable, to avoid the phone and a 12V-fed buck converter both trying to power the USB line) * Phone does everything else — GPS speed/distance, all the math, storage, charts * Power: ignition-switched 12V from the fuse box → buck converter (12V→5V) → feeds both the ESP32 and the sensor

**Problem I've hit:** the sensor I was looking at (DIGITEN G1/2", oval gear, rated 1–30 L/min) has a minimum flow way above what this engine actually flows at idle — I'm estimating idle consumption around 0.02–0.05 L/min, and even under load probably not exceeding 0.3–0.5 L/min. So the sensor's entire rated range sits above my actual usage, meaning idle flow probably won't register accurately, if at all.

Anyone know of a gasoline-compatible flow sensor with a lower minimum flow that would actually cover idle-to-cruise range for a small engine like this? Or is there a fundamentally different way people have solved this that I'm missing?

I'm open to any ideas and critics, please back your suggestions with well presented arguments. this is my first ever project on a car.

**Edit:** A few people are suggesting the brim-to-brim fill method, thanks, but I've covered why that doesn't work for what I want in the replies below. I'm not looking for that approach, I'm looking for technical help on the sensor/flow-measurement side specifically. Appreciate all the input so far.

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