Always Know Your Real Cost Per Mile

You know what you spent on gas last month. Sort of. Maybe you looked at your credit card statement and had a vague sense of the total. But do you know your actual MPG for that tank? What about the trend over the last six months? How does your efficiency this winter compare to last summer? Is that drop in MPG normal — or is it a sign your engine is running rich, your tires are underinflated, or your alignment is off?

Most people have no idea. And without that data, you’re not just flying blind on efficiency — you’re missing one of the cheapest and earliest diagnostic signals your car gives you.

OpenClaw can track every fill-up, calculate real MPG per tank, log expenses, and tell you when something changes. It turns a habit you’ve never thought about into data you can use.

The Problem With Not Tracking

Gas is your second-largest variable expense after rent or mortgage for most commuters. For someone driving 15,000 miles a year at $3.50/gallon with a 30 MPG car, that’s $1,750 annually. A 10% drop in efficiency — from 30 MPG to 27 MPG — costs you $175 a year. You wouldn’t knowingly waste $175. But without tracking, you never know it’s happening.

The efficiency signal is also a maintenance early warning. A sudden drop in MPG often appears before other symptoms. Bad oxygen sensors, misaligned wheels, underinflated tires, a clogged air filter — all show up as reduced efficiency first. Catching it early means catching it cheaply. But you have to be watching.

How It Works

Logging a Fill-Up

When you fill up, send OpenClaw the basics:

“Prius fill-up: 9.2 gallons, $28.47, odometer 47,892. Shell on Broadway.”

OpenClaw parses this and adds it to your vehicle fuel log:

## Fill-Up Log — Prius

| Date | Odometer | Gallons | Price/Gal | Total | MPG (tank) | Notes |
|------|----------|---------|-----------|-------|------------|-------|
| Jun 19 | 47,892 | 9.2 | $3.095 | $28.47 | 34.1 | Shell Broadway |
| Jun 5 | 47,245 | 8.8 | $3.18 | $27.98 | 33.6 | Chevron |
| May 21 | 46,615 | 9.1 | $3.25 | $29.58 | 32.8 | Shell — started highway trip |

The MPG is calculated from the distance since the last fill-up (current odometer minus previous). OpenClaw flags outliers: if your tank MPG suddenly drops from 34 to 28, it asks if something changed — new driving pattern, heavy cargo, cold weather — or if it should flag a potential maintenance issue.

Running MPG vs. Lifetime Average

Over time, OpenClaw tracks your rolling average:

📊 PRIUS — Fuel Summary (Last 5 Fill-ups)

• Average MPG (rolling): 33.6
• Lifetime average: 34.1
• Efficiency trend: ↓ 1.5% (3-month rolling vs. lifetime)
• Total spend (last 30 days): $112.83
• Gallons used (last 30 days): 34.6

💡 Note: Your 3-month rolling average (33.6 MPG) is tracking slightly below your lifetime average (34.1). This could be weather-related — winter typically drops MPG 5-8%. If it's not winter, consider checking tire pressure or scheduling a service check.

Budget Tracking

Set a monthly fuel budget:

“Set my monthly fuel budget to $200 for the Prius.”

OpenClaw tracks cumulative spend and warns you when you’re on track to exceed it:

“⚠️ Prius fuel spend: $167 through the 19th. On pace for ~$263 this month (budget: $200). The main driver is price — you’ve averaged $3.20/gallon vs. your $2.90 assumption. Gallons used is actually slightly below budget pace.”

This is useful because there are two ways to bust a fuel budget: driving more or prices going up. OpenClaw separates them, so you know whether you need to drive less or just accept higher prices.

Efficiency Anomaly Detection

This is where it pays off. OpenClaw monitors for MPG drops that can’t be explained by context:

”📉 PRIUS — Efficiency Alert

Tank MPG: 28.4 (vs. rolling average 33.6) Distance since last fill-up: 281 miles on 9.8 gallons

This is the lowest tank MPG in 6 months. No weather or driving pattern explanation logged.

Possible causes: tire pressure drop, degraded oxygen sensor, dirty air filter, driving pattern change. Recommend checking tire pressure first — it’s free and takes 2 minutes.”

You don’t need to be watching for this. OpenClaw is.

Comparing Vehicles

If you have multiple vehicles, OpenClaw can compare them:

“Compare fuel costs for the Prius and the Subaru.”

🚗 PRIUS (2022)
• Avg MPG: 34.1 | Cost/mile: $0.091
• Spend (last 30 days): $112.83
• Best tank: 36.8 mpg (May 3)

🚙 SUBARU (2019)
• Avg MPG: 24.3 | Cost/mile: $0.132
• Spend (last 30 days): $189.47
• Best tank: 26.1 mpg (Apr 12)

📊 SUBARU COSTS 45% MORE PER MILE

If you’re deciding whether to take the Subaru on a long trip versus renting something efficient, OpenClaw can calculate the cost difference.

Setting Up the Cron Job

A weekly check-in keeps your data fresh and surfaces trends before they become expensive:

{
  "schedule": { "kind": "cron", "expr": "0 9 * * 1", "tz": "America/Vancouver" },
  "payload": {
    "kind": "agentTurn",
    "message": "Review the fuel log at ~/vehicles/fuel-log.md for all vehicles. Check rolling MPG vs. lifetime average. Flag any tank with MPG more than 10% below the vehicle's rolling average without a logged explanation. Check cumulative monthly spend vs. budget for each vehicle. Send a concise summary with any alerts."
  },
  "delivery": { "mode": "announce" },
  "sessionTarget": "isolated"
}

Monday morning, your fuel summary arrives. You see the numbers, any anomalies, and where you stand on budget. It takes 30 seconds to log the weekend’s fill-up and 30 seconds to read the summary.

What You Need to Set It Up

• OpenClaw on Telegram or any messaging channel
• A fuel log file — one per vehicle, starts empty and builds over time
• Your first fill-up entry — to set the baseline
• A budget (optional) — set a monthly target per vehicle

That’s it. No OBD-II reader, no Bluetooth, no app. Just start logging when you fill up.

Limitations

Manual logging is required — OpenClaw can’t read your fuel gauge. You have to send the data when you fill up. If you never log, nothing happens.

MPG accuracy depends on fill-to-fill consistency — The most accurate MPG tracking comes from filling the tank completely every time. If you frequently add a few gallons without topping off, your tank MPG numbers will be noisy. Log a note if you didn’t fill completely and OpenClaw will note the measurement may be imprecise.

No trip-specific segmentation — OpenClaw calculates tank MPG and rolling averages. It doesn’t automatically know that the tank ending at 46,615 was a highway trip versus a commute week. You can add notes, but it won’t infer it.

Gas price tracking is local — OpenClaw logs the prices you report. It doesn’t pull real-time gas prices. If you want to know if you should fill up before prices rise, that’s a separate check.

Doesn’t track total cost of ownership — This is fuel and fuel-related expense tracking. Insurance, registration, and maintenance are separate systems (you could extend this setup to track those, but it’s not built in by default).

Why This Works

Most people know roughly what they spend on gas but have no idea if that number is normal, whether it changed, or why. The difference between 30 MPG and 33 MPG at $3.50/gallon over 15,000 miles is $175 — comparable to a full oil change. You’re either paying that in efficiency or keeping it.

OpenClaw makes the logging frictionless enough that you actually do it. One message after every fill-up. The weekly summary makes the data actionable. The anomaly detection catches problems early.

You don’t need to think about it. It thinks about it for you — and tells you when there’s something worth knowing.