# Diesel Fuel System Leak Repair in Upland > Smell diesel or see drips under your truck? Route 66 Auto Repair in Upland traces diesel fuel leaks to the source and quotes the fix in writing. Source: https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-system-leak-repair Updated: 2026-09-17 Business: Route 66 Auto Repair, 1775 W Foothill Blvd, Upland, CA 91786, (909) 608-7699 Hours: Monday to Friday 8 AM–5 PM, Saturday 8 AM–2 PM, Sunday closed **TLDR:** Any diesel leak is worth checking fast. We **trace the leak to its origin**, photograph it, and give a **written estimate** before any repair. Diesel fuel leak repair finds and fixes fuel escaping from filters, lines, pumps or injector fittings. Route 66 Auto Repair in Upland treats any diesel leak as a priority: fuel on a hot exhaust or a slick of diesel under your tire is a safety issue. ASE-certified technicians trace the wet trail to where it starts, photograph it, and write an estimate before a fitting is replaced. ## Where do diesel fuel leaks usually show up? - Diesel smell in the cab after the heater runs - Wet film around the fuel filter housing or water separator - Drips under the frame rail along the supply line - Fuel mist on the engine near injector lines - Stains on the driveway that feel oily and smell like diesel - Fuel economy dropping with no change in driving ## Why does the pressure side matter? The supply side runs at low pressure, so a leak there drips or seeps. The injection side can run at very high pressure. A pinhole there sprays a fine mist that can ignite on hot parts or cut skin. Never feel for a leak with your hand on a running diesel. We inspect high-pressure fittings with the engine off and use clean-and-watch methods rather than touching anything live. If the source is a seal at the injector, our [diesel fuel injector seal replacement](https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-injector-seal-replacement) page covers that repair. ## Our diesel fuel leak repair process 1. **Clean the area:** Old fuel and grime are cleaned off so a fresh leak is easy to see. 2. **Run and watch:** The engine is run and the system pressurized while we watch from a safe distance. 3. **Mark and photograph:** The leak point is marked and photographed so you can see what we saw. 4. **Repair and retest:** Seals, lines or fittings are replaced, torqued to spec, and rechecked after a road test. ## What's included in diesel fuel leak repair - Degrease and visual trace of the fuel system - Supply and return line inspection along the frame - Filter housing and separator seal check - Photos of the leak point - Replacement seals or lines as approved - Post-repair leak check after a road test ## Is it a need-now or need-later repair? **Need now:** - Any fuel on or near the exhaust - Active dripping or a strong smell in the cab - Spray from a high-pressure fitting **Need later:** - Light dampness on a return hose with no drip - An old filter housing seal that is just starting to sweat ## How pricing and timing work A seal at the filter housing is a short job. A line routed over the transmission or behind the engine takes more labor. Many leaks are found and fixed the same day when the board allows. We state the diagnostic fee at the counter before testing, and AAA members save 10% up to $75 on parts and labor. For a full line replacement, see [diesel fuel line repair](https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-line-repair). ## Aftercare Some smell can linger for a day as fuel burns off hot parts. Fresh drips after that need a look. A [diesel fuel line pressure testing](https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-line-pressure-testing) check confirms the repair holds. ## Frequently asked questions ### Is a diesel fuel leak a fire risk? Diesel is harder to ignite than gasoline, but spray on a hot turbo or exhaust manifold can still catch. Treat it as a need-now repair. ### Can I use tape or sealant on a fuel line? No. Fuel dissolves most tapes, and high-pressure lines need the correct fitting and torque. A temporary patch can fail on the freeway. ### Why does my cab smell like diesel but I see no drips? Leaks near the firewall or on top of the engine can evaporate before they drip. The fresh-air intake then pulls the smell into the cab. A cleaned engine bay and a run test usually find it. --- Call (909) 608-7699 or visit https://route66autorepairshop.com/contact for a written estimate.