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A diesel fuel system contamination test checks your fuel for water, dirt, microbial growth and the wrong fuel. Route 66 Auto Repair in Upland runs it on diesel pickups and vans after a questionable fill-up, a water-in-fuel light, or repeated filter clogs. Our ASE-certified technicians sample from the tank and filters, show you what they found, and tell you in writing what needs to happen next.
When should you test for fuel contamination?
- Right after putting gasoline in a diesel by mistake (do not start it)
- Water-in-fuel light that returns after draining
- Rough running right after a fill-up at an unfamiliar station
- Dark, cloudy fuel in the separator bowl
- Repeat injector or pump failures
What if you put gasoline in your diesel?
Do not start the engine, or shut it off right away if you already did. Gasoline removes the lubrication that the high-pressure pump depends on. Have it towed in rather than driving. We accept tow-ins and have an after-hours key drop.
Once here, we test the fuel, drain the tank and lines if needed, replace filters, and check pump and injector behavior. If contamination is heavy, diesel fuel tank cleaning or a diesel fuel system flush follows.
Our contamination test process
Step 1: Sample
Fuel is drawn from the tank bottom, the separator and the filter into clear containers.
Step 2: Inspect
Samples are checked for water separation, sediment, color, smell and growth.
Step 3: Check filters
Filter media is examined for debris and slime.
Step 4: Report
Findings and next steps are written up, with photos of the samples.
What's included in a contamination test
Included on the work order
- 01Tank bottom fuel sample
- 02Separator and filter sample
- 03Visual water and sediment check
- 04Filter media inspection
- 05Photos of samples
- 06Written cleanup recommendations
Is it a need-now or need-later repair?
Need now: call
- Gasoline or heavy water in the fuel
- Stalling or no-start from contamination
Need later: book
- Slight haze with no drivability symptoms
- Light sediment in an old filter
How pricing and timing work
The test itself is usually quick. Cleanup cost depends on what we find: a filter change, a drain, a tank cleaning, or checks on the pump and injectors. The diagnostic fee is stated at the counter before testing and applies to approved related repair. For symptoms beyond the fuel, diesel fuel system diagnostics goes further.
Aftercare
Keep your receipt if you suspect a bad fill; the station may want it. Drain the separator as your manual says, and have a sample checked again at the next filter change if the result was borderline.
Frequently asked questions
Can I drive after putting gas in my diesel?
No. Gasoline can damage the injection pump quickly. Leave it off and have it towed in.
How does water get into diesel?
From condensation in the tank, poorly kept station tanks, or a failed cap seal. Diesel holds water more readily than gasoline.
Will you send a sample to a lab?
Our test is a shop inspection. If you need a lab report, for example for a claim, we can help you collect a clean sample.