n8n Fuel Tank Variance Investigation: Sheets, Gemini & Slack

Detect and explain fuel tank variances automatically—using Sheets, Gemini, and Slack

When a shift closes, this n8n Fuel Tank Variance Investigation workflow receives a webhook, reconciles tank wet-stock in Google Sheets, optionally calls Google Gemini to summarize anomalies, and immediately posts investigation alerts to Slack—all while logging a full audit record.

What this workflow does

• Receives a shift-close POST webhook with station_id and shift_id.
• Fetches reconciliation inputs from Google Sheets, including active tanks, shift tank readings, nozzle totalizer sales, deliveries, and prior audit history.
• Calculates per-tank closing variance by comparing expected vs actual closing volume, applying tolerance and determining variance direction (loss or surplus).
• Runs risk & pattern checks, including a baseline z-score, drift patterns, and identification of data gaps or possible meter/delivery issues.
• Triggers AI investigation when needed: for variances warranting review, the workflow sends the computed context to Google Gemini to generate a non-accusatory JSON investigation summary with likely causes and recommended actions.
• Writes results to Audit_Log in Google Sheets, including the full reconciliation record and any AI verdict/summary.
• Posts Slack notifications for tanks that need attention (alerts, critical variances, delivery shortfalls, or data gaps) and returns a JSON response to the webhook caller.

Use cases

• Automatic shift-end reconciliation for retail fuel operations where tank wet-stock must match expected sales/deliveries.
• Fast investigation routing when z-score/risk thresholds indicate unusual loss/surplus or missing data.
• AI-assisted, structured anomaly notes for auditing teams—without accusatory language.

Technical details

• Integrations/nodes: Webhook, Google Sheets (Service Account), Slack, and optional Google Gemini.
• Workflow building blocks: if, code, merge, slack, webhook, sticky note.

Category: n8n automation workflow — designed for automation engineers and SaaS operators who need reliable variance detection and audit logging with actionable alerts.