Same fuel, same water, same 165 GPH. One separator let 42% of the water through.
FASS paid $14,000 to have 19 filters and water separators run through independent multipass testing at SGS IBR Laboratories in June 2020. Below are the transcribed numbers from every report, with the flow rate each one was run at, because a separation percentage means nothing without it.
- Lab
- SGS IBR
- Tested
- June 2020
- Filters in test
- 19
- Run length
- 50 min
- Water dosed
- 60 mL
The only fair comparison: everything run at 165 GPH
Six filters and separators were tested at 165 gallons per hour, so these can be read against each other directly. Percentages are cumulative water separation at the 50-minute mark.
| Filter | Water removed | Scale | SGS test |
|---|---|---|---|
| FASSXWS-3002XL | 99.3% | 21275A1 | |
| FASSXWS-3002 | 99.1% | 21275A2 | |
| BaldwinBF1212 | 98.8% | 21275A4 | |
| DonaldsonP551001 | 98.6% | 21275A5 | |
| Caterpillar175-2949 | 97.8% | 21275A3 | |
| FleetguardFS1001 / Cummins 3413084 | 97.7% | 21275A6 | |
| AirDogWS100 | 58.1% | 21275A7 |
Worth saying plainly: the OEM and cross-reference filters in this test performed well. Baldwin, Donaldson, Caterpillar and Fleetguard all cleared 97% at 165 GPH. The separation gap here belongs to one product, the AirDog WS100, not to every filter that isn't a FASS.
What 58% looks like in your tank
Take 100 gallons of water passing through the separator over the life of a filter. This is how much of it keeps going toward the injection pump, the rail and the injectors.
Water does not hurt performance. It builds rust in the three most expensive parts of the fuel system.
Rust forms inside the injection pump, the fuel rail and the injector bodies, which hold the tightest tolerances in the truck. It restricts fuel delivery first, then flakes loose and travels downstream through everything it touches. A pump, a rail and a set of injectors is a four-figure repair on most platforms and a five-figure one on some.
Separation falls as flow rises. FASS barely moves.
Faster fuel gives water droplets less time to coalesce and drop out, so most separators lose efficiency as you push volume through them. The XWS-3002XL was run at three flow rates and stayed within half a point. The AirDog WS100 never got near it at either rate it was run.
Blue: FASS XWS-3002XL, tests 21275B2, 21275A1 and 21275E2. Grey: AirDog WS100, tests 21275A7 and 21275D2.
The same effect shows up in the Caterpillar 175-2949, which came in at 99.1% when run at 100 GPH and 97.8% at 165 GPH. If a manufacturer quotes you a separation number without a flow rate attached, it is not a specification.
Every test, transcribed
All sixteen runs, with flow rate and emulsion droplet size. D50 is the median droplet diameter of the water emulsion the filter was asked to separate. Larger droplets separate more easily, so it belongs next to the result.
| Filter | Water removed | Flow | D50 | SGS test |
|---|---|---|---|---|
| FASSXWS-3002XL | 99.4% | 100 GPH | 28 µm | 21275B2 |
| FASSXWS-3002XL | 99.3% | 165 GPH | 17 µm | 21275A1 |
| FASSXWS-3002 | 99.1% | 165 GPH | 16 µm | 21275A2 |
| FASSXWS-3002XL | 98.9% | 250 GPH | 9 µm | 21275E2 |
| FASSXWS-3002 | 98.9% | 250 GPH | 5 µm | 21275E1 |
| AirDogWS100 | 60.6% | 200 GPH | 10 µm | 21275D2 |
| AirDogWS100 | 58.1% | 165 GPH | 17 µm | 21275A7 |
| BaldwinBF1212 | 98.8% | 165 GPH | 19 µm | 21275A4 |
| Caterpillar175-2949 | 99.1% | 100 GPH | 24 µm | 21275B5 |
| Caterpillar175-2949 | 97.8% | 165 GPH | 18 µm | 21275A3 |
| Cummins FleetguardFS1212 | 98.9% | 100 GPH | 29 µm | 21275B6 |
| DonaldsonP551001 | 98.6% | 165 GPH | 17 µm | 21275A5 |
| DonaldsonP558000 | 94.6% | 100 GPH | 26 µm | 21275B3 |
| FleetguardFS1001 / Cummins 3413084 | 97.7% | 165 GPH | 17 µm | 21275A6 |
| PACCARK37-1027-310010 | 99.1% | 200 GPH | 8 µm | 21275D1 |
| Racor900MA | 98.5% | 90 GPH | 23 µm | 21275C |
Source: SGS IBR Laboratories, Multipass fuel/water separation, ULSD, 60 mL water, 22-24 C, 50-minute run, June 2020, corrected 10 July 2020. Commissioned and paid for by FASS Diesel Fuel Systems. Every figure above is the 50-minute cumulative separation value from the report named in the last column; scans are below.
Water is one of three things in your fuel
A separator that only catches water still leaves two problems on the truck. A FASS system handles all three before fuel reaches the injection pump.
Water
Separated and held in the bowl, then drained at service. 99%+ on the Extreme Water Separator across every flow rate tested.
Entrained air and vapor
Aerated fuel throws off injection timing, because compressible vapor does not behave like liquid fuel under pressure. FASS separates air and vapor and returns it to the tank instead of sending it to the engine.
Particulate
Dirt and abrasive contamination are filtered to 2 micron absolute, finer than most OEM-spec filters on a modern diesel.
The raw lab reports
Every sheet below came back from SGS IBR and is reproduced unedited. Open any one to read the full multipass data, including the reading at each five-minute interval.
FASS
AirDog
Racor
PACCAR
Caterpillar
Fleetguard
Cummins Fleetguard
Donaldson
Baldwin
Questions people ask about this test
How much water does a FASS Extreme Water Separator remove?
At 165 GPH the XWS-3002XL removed 99.3% of the water in the fuel and the XWS-3002 removed 99.1%, measured as cumulative separation at the end of a 50-minute multipass run. FASS publishes these as 99.34% and 99.08% from the same test set.
How did the AirDog WS100 compare at the same flow rate?
It removed 58.1% at 165 GPH, and 60.6% in a separate run at 200 GPH. Those are the two lowest results anywhere in the test group.
Did the OEM filters do badly too?
No, and we are not going to claim otherwise. Baldwin, Donaldson, Caterpillar, Fleetguard, PACCAR and Racor all landed between 94.6% and 99.1% depending on part and flow rate. The separation gap in this test is specific to the AirDog unit, not to every non-FASS filter.
Why does flow rate matter when reading these numbers?
Separation efficiency falls as flow rises, because faster fuel gives water droplets less time to coalesce and drop out. The Caterpillar 175-2949 shows it directly: 99.1% at 100 GPH, 97.8% at 165 GPH. Only filters run at the same flow rate can be compared to each other.
Why does water in diesel fuel matter?
Water corrodes the injection pump, fuel rail and injectors. Rust restricts fuel delivery, then breaks loose and travels downstream, which is how a water problem becomes a multi-thousand-dollar injection system repair.
Who ran the test?
SGS IBR Laboratories in Grass Lake, Michigan, an independent third-party lab. FASS commissioned and paid for the testing and published the raw reports.
Put a tested separator on your truck
FASS Motorsports stocks the full FASS Diesel Fuel Systems lineup and ships same day on in-stock systems.
