Description
Product Overview
The FS1242 Spin-On Fuel Water Separator Filter is a high-performance replacement filter engineered for diesel engines requiring premium fuel-water separation. As a direct upgrade to the Fleetguard FS1015/FS1015B series, this 10-micron element delivers 96% water separation efficiency to protect your fuel system from water contamination, rust, and particulate debris. Designed for Cummins 8.3L ISC and QSC engines commonly found in Freightliner medium-duty trucks, Kenworth T300, Peterbilt 330, buses, marine vessels, and industrial power equipment.
Key Features
-
10-Micron High-Efficiency Media: Premium pleated cellulose/synthetic blend media captures 96% of emulsified water and 99% of solid particles ≥10 microns. Protects high-pressure common rail injectors and CP3/CP4 fuel pumps from abrasive wear and internal corrosion.
-
Tool-Free Spin-On Design: Quick-twist installation with pre-lubricated O-ring seals. Standard 1-14 UNS-2B thread — hand-tighten 3/4 to 1 turn after gasket contact. Typical replacement takes under 10 minutes with basic hand tools.
-
Direct FS1015/FS1015B Upgrade: Shares identical thread pitch, gasket diameter, and canister dimensions with FS1015, FS1015B, and 3355903 Fleetguard filters. Larger pleat count provides up to 15% more filtration surface area versus OE equivalent.
-
Heavy-Duty Steel Construction: Corrosion-resistant coated steel canister rated for diesel fuel system pressures up to 15 PSI. Operating temperature range: -40°F to +250°F (-40°C to +121°C).
-
Anti-Drain Back Valve: Integrated silicone valve retains fuel in the filter housing when the engine is off, preventing hard starts and reducing injector stiction on cold mornings.
-
Complete Gasket Kit Included: Each filter ships with 2 replacement O-rings — one for the mounting base seal and one for the collection bowl interface. No need to source gaskets separately.
Compatibility
This FS1242 fuel water separator filter fits the following engine and vehicle applications when equipped with the FS1242-compatible spin-on filter housing:
| Engine |
Application |
| Cummins 6CT8.3 / ISC 8.3L |
Freightliner FL70, FL80, M2 106; Kenworth T300, T370; Peterbilt 330, 335; International 4000-Series |
| Cummins QSC 8.3L |
Marine propulsion engines (QSC8.3-500/550/600), industrial generators, construction equipment, irrigation pumps |
| Cummins 6CTA8.3 |
Agricultural tractors, combines, stationary power units, wood chippers |
| Fleetguard FS1242 Housing |
Requires 3831871S collection bowl + 142784S mounting base (reuse existing — filter only) |
⚠️ Fitment Note: This listing includes the spin-on filter element and 2 O-rings only. The 3831871S collection bowl and 142784S mounting base are reusable components from your existing filter housing assembly. Verify your housing matches the FS1242/FS1015 thread pattern before ordering.
Specifications
| Specification |
Value |
| iFJF Part Number |
FJ-1242 |
| Filter Type |
Spin-On Fuel Water Separator |
| Filtration Rating |
10 Micron (Nominal) |
| Water Separation Efficiency |
96% (SAE J1488) |
| Thread Size |
1-14 UNS-2B |
| Outer Diameter |
3.74 in (95 mm) |
| Height |
6.81 in (173 mm) |
| Weight |
0.8 kg (1.76 lbs) |
| Gasket Type |
Nitrile (NBR) O-Ring × 2 |
| Max Working Pressure |
15 PSI (1.03 bar) |
| Service Interval |
Every 10,000-15,000 miles or 12 months |
Cross Reference
| Brand |
Part Numbers |
| Fleetguard / Cummins |
FS1242, FS1015, FS1015B, 3355903 |
| Baldwin |
BF1249-O |
| Donaldson |
P551864 |
| WIX / MANN-Filter |
95242, 33242, WK940/36X |
| Luber-finer |
LFF1017 |
| Fleetrite |
31701062 |
| Purolator |
PS6829, 86242 |
| Other |
6003113610, SK426, DS170 |
Why Choose iFJF FS1242
Every iFJF FS1242 filter is manufactured to meet or exceed Fleetguard OEM specifications at a competitive aftermarket price. Our multi-stage quality control includes: burst pressure testing (150% rated), micron efficiency verification via ISO 19438 multipass testing, O-ring material compatibility checks across diesel and biodiesel blends up to B20, and 100% leak-tested canister seams. Backed by a 1-year warranty and US-based customer support, you get OEM-grade protection without the dealership markup. Thousands of diesel owners and fleet operators trust iFJF filters for their daily operation.
Installation Guide
-
Prepare: Park on level ground. Relieve fuel system pressure and drain the 3831871S collection bowl into an approved container.
-
Remove Old Filter: Use a filter wrench if needed. Clean the mounting base sealing surface with a lint-free shop towel — debris on the seal face is the #1 cause of leaks.
-
Lubricate Gaskets: Apply a thin film of clean diesel fuel to both new O-rings. Never install dry — this prevents gasket binding and twisting during spin-on.
-
Install New Filter: Spin on by hand until the gasket contacts the mounting base, then tighten an additional 3/4 to 1 full turn by hand only. Do not use a filter wrench for installation — over-tightening damages the gasket and canister seal.
-
Prime System: Cycle the key to RUN (not START) 3-4 times to activate the lift pump and purge air. Or use the manual primer if equipped. Start engine and check for leaks at idle.
Frequently Asked Questions
Q: Will this FS1242 filter fit my Freightliner FL70 with Cummins 8.3L?
A: Yes. This filter is a direct fit for Freightliner FL70, FL80, and M2 106 models equipped with the Cummins 6CT8.3 or ISC 8.3L engine and the FS1242/FS1015-compatible spin-on filter housing. Verify your existing filter part number or housing thread size if unsure.
Q: What's the difference between FS1242 and FS1015?
A: FS1242 is the current Fleetguard part number that supersedes FS1015 and FS1015B. Both share identical thread dimensions (1-14 UNS-2B), gasket diameter, and 10-micron filtration rating. The FS1242 specification may include a higher pleat count and improved water-holding capacity depending on manufacturing series.
Q: How often should I replace this fuel water separator?
A: Replace every 10,000-15,000 miles or 12 months, whichever comes first. Shorten the interval if you: operate in high-humidity environments, use biodiesel blends above B5, notice reduced engine power or rough idle, or see water in the collection bowl more frequently than usual.
Q: Do I need to buy the bowl and base separately?
A: No — this listing is the replacement filter element only. Your existing 3831871S collection bowl and 142784S mounting base are designed to be reused for the life of the vehicle. You only need to purchase the spin-on filter cartridge (with included O-rings) for each routine service.
Q: Is this filter suitable for marine diesel engines?
A: Yes. This FS1242 filter is compatible with Cummins QSC 8.3L marine propulsion and auxiliary engines. We recommend more frequent replacement intervals (every 6 months or 250 hours) in marine applications due to elevated humidity, potential fuel condensation, and the critical nature of marine engine reliability.
