# Diesel Fuel System Contamination Test in Upland

> Bad fuel fill or water warning on your diesel? Route 66 Auto Repair in Upland tests fuel for water, debris and gasoline before you pay for bigger repairs.

Source: https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-system-contamination-test  
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:** Before replacing fuel parts, **test the fuel**. We sample it, **show you the results**, and plan the cleanup from there.

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](https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-tank-cleaning) or a [diesel fuel system flush](https://route66autorepairshop.com/diesel-engine-services/diesel-fuel-system-flush) follows.

## Our contamination test process

1. **Sample:** Fuel is drawn from the tank bottom, the separator and the filter into clear containers.
2. **Inspect:** Samples are checked for water separation, sediment, color, smell and growth.
3. **Check filters:** Filter media is examined for debris and slime.
4. **Report:** Findings and next steps are written up, with photos of the samples.

## What's included in a contamination test

- Tank bottom fuel sample
- Separator and filter sample
- Visual water and sediment check
- Filter media inspection
- Photos of samples
- Written cleanup recommendations

## Is it a need-now or need-later repair?

**Need now:**
- Gasoline or heavy water in the fuel
- Stalling or no-start from contamination

**Need later:**
- 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](https://route66autorepairshop.com/diesel-engine-services/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.

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Call (909) 608-7699 or visit https://route66autorepairshop.com/contact for a written estimate.