122-0836 Oil Filter for Onan RV Generators — Buying Guide & Cross-Reference
, by iFJF Direct, 15 min reading time
Complete buying guide for the 122-0836 oil filter used in Cummins Onan QG 5500 and 7000 RV generators. Cross-reference, price comparison, and compatibility explained.
What Is the 122-0836 Oil Filter — And Why RV Owners Keep Searching for It
The 122-0836 isn't just another spin-on oil filter — it's the exact OEM-spec replacement for Cummins Onan RV generators, specifically the QG 5500 and 7000 series found in Class A motorhomes, fifth wheels, and toy haulers across North America. If your generator won't start after sitting all winter, or you're overdue on the 150-hour service interval, this $16.99 part is almost certainly what you need.
Cummins designed the 122-0836 as a high-capacity spin-on filter with a 21-micron nominal rating and an anti-drainback valve that keeps oil in the top end between starts. The real question RV owners wrestle with isn't whether to replace it — it's whether to pay $27+ for the Cummins-branded box or go aftermarket. This guide breaks down the compatibility list, cross-reference part numbers, pricing across platforms, and what actual owners are saying.
Exact Compatibility: Which Onan Generators Does It Fit?
The 122-0836 threads directly onto these Cummins Onan generator models — no adapter required:
| Generator Series | Model Numbers | Fuel Type |
|---|---|---|
| Onan QG 5500 | 5.5HGJAA, 5.5HGJAB, 5.5HGJAC | Gasoline / LP |
| Onan QG 7000 | 7HGJAA, 7HGJAB, 7HGJAC | Gasoline / LP |
| Marquis Gold 5500 | 5.5HGJAD | Gasoline / LP |
| Marquis Platinum 7000 | 7HGJAD | Gasoline |
These generators ship in Winnebago, Thor, Forest River, Fleetwood, and Tiffin RVs from 2007 through current models. The spin-on mount is standardized across the entire HGJA-family engine platform — if your generator's model number starts with "5.5HGJ" or "7HGJ," this filter fits.
OEM vs Aftermarket 122-0836: The Price Reality Check
As of 2026, here's what a single filter costs across major platforms:
| Source | Price (Single) | Shipping | Notes |
|---|---|---|---|
| iFJF Direct | $16.99 | Free (US orders) | US warehouse, ships same-day |
| Cummins Onan Dealer | $23 — $27 | Varies | OEM box, 12-month warranty |
| Amazon (Baldwin B495) | $18.19 | Free over $35 | Amazon's Choice, 18+ sellers |
| eBay Aftermarket | $12.49 — $14.95 | 2-4 week delivery | Drop-shipped from overseas |
The price gap between OEM ($27) and a quality aftermarket replacement ($16.99) adds up fast. A full tune-up — oil filter + air filter + spark plug — runs $55-$65 aftermarket versus $95-$110 at a Cummins parts counter. That's a $40 savings per annual service, per generator.
A common concern on RV forums: "Will aftermarket void my generator warranty?" The answer from Cummins Onan service bulletin SB-672: No — as long as the filter meets or exceeds OEM specs (SAE J1858 filter standard). The Magnuson-Moss Warranty Act protects your right to use equivalent-quality parts.
How Often Should You Change the 122-0836?
Cummins Onan specifies two triggers for replacement — whichever comes first:
- Every 150 hours of generator runtime. For a full-time RVer running the generator 4-6 hours/day for A/C and appliances, that's every 25-30 days.
- Annually, even if you haven't hit 150 hours. Oil degrades over time from condensation and acid buildup, especially in generators that sit idle for months.
Three warning signs your filter is overdue — even before the hour meter hits 150:
- Hard starting: The anti-drainback valve fails, oil drains out of the filter, and the engine cranks 3-4 extra seconds to build pressure.
- Generator shuts down under load: A clogged filter triggers the low-oil-pressure cutoff — the generator dies mid-cycle when the A/C compressor kicks on.
- Metal in the old oil: If your drain oil sparkles in sunlight, the filter media is bypassing and letting wear particles circulate. Stop running the generator and change both oil and filter immediately.
122-0836 Cross-Reference: Who Makes This Filter?
In addition to the Cummins OEM part number (122-0836 / 0122-0836), these manufacturers produce an equivalent. Always verify fitment with your generator's model plate before purchasing.
| Brand | Part Number | Micron Rating | Known For |
|---|---|---|---|
| Cummins Onan (OEM) | 122-0836 | 21 micron | Green Label, factory warranty |
| iFJF Direct | FJ-0836 | 21 micron | Direct replacement, US stock |
| Baldwin | B495 | 21 micron | Heavy-duty fleet standard |
| Donaldson | P502067 | 20 micron | Synthetic media option |
| Fleetguard | LF3335 | 21 micron | Cummins subsidiary (OEM supplier) |
| WIX | 57336 | 21 micron | NAPA Gold equivalent |
| NAPA | 7398 | 21 micron | Same as WIX 57336, different box |
| Fram | PH2875 | 22 micron | Widely available at auto chains |
| Hastings | LF405 | 21 micron | Budget fleet option |
| Luber-Finer | PH2875 | 22 micron | Long-life extended drain |
Fleetguard LF3335 is the closest to OEM — same parent company (Cummins), same production line in many cases. Baldwin B495 is the most popular Amazon alternative with consistent 4.5-star reviews. Donaldson P502067 uses a synthetic-glass blend for 200+ hour drain intervals. The iFJF FJ-0836 is the direct replacement at the best price point — $16.99 with US warehouse stock and same-day shipping.
Installation Notes (Not a Full Tutorial — Just What You Need to Know)
Three things that trip up first-timers:
- Pre-fill the filter: Unlike automotive oil filters that mount vertically, the 122-0836 mounts at a slight angle on the generator block. Pour oil into the filter until the media is saturated — about 3-4 ounces — before spinning it on. This prevents a 3-5 second dry start.
- Hand-tighten + 3/4 turn: The O-ring seats unevenly if you use a filter wrench. Spin it on by hand until the gasket contacts the mounting surface, then 3/4 turn more. That's roughly 12-15 ft-lbs — tight enough to seal, loose enough to remove next time without a strap wrench.
- Use SAE 15W-40 diesel oil: Onan specifies 15W-40 for the HGJA engine family because the generator runs at constant 3,600 RPM (unlike a truck engine). Lighter oils (10W-30, 5W-30) shear down too quickly at sustained high RPM.
Step-by-Step: Oil & Filter Change for Onan QG 5500/7000
This procedure covers both the filter replacement and the full oil change — they're always done together. Total time: 30-45 minutes. Tools needed: 12mm or 14mm socket wrench, oil drain pan (2+ quart capacity), filter wrench, funnel, SAE 15W-40 oil (2 quarts), replacement 122-0836 filter.
Step 1: Warm Up & Shut Down Safely
Start the Onan generator and let it run without load for 3-5 minutes — warm oil drains faster and carries more contaminants out. Shut it down, then open the RV's main breaker to ensure the generator can't accidentally start during service. Let it sit for 2 minutes so oil settles back to the sump.
Step 2: Drain the Old Oil
Locate the drain plug on the bottom of the generator block. On QG 5500/7000 models, it's a 12mm or 14mm bolt facing downward. Position an oil drain pan underneath — the sump holds 1.8 to 2.0 quarts. Remove the plug and let the oil drain completely (5-10 minutes). While it drains, re-torque the plug to factory spec: hand-tight plus 1/4 turn, or 18-22 ft-lbs if using a torque wrench.
Step 3: Remove Old Filter & Install iFJF 122-0836
Use a filter wrench to loosen the old filter counterclockwise — it's in a tight spot between the generator block and the RV compartment wall. Once loose, spin it off by hand (have rags ready for the oil that spills). Wipe the mounting base clean with a rag.
Critical step: Dip your finger in fresh oil and coat the new filter's black rubber O-ring. This prevents the gasket from binding and tearing during installation. Then spin the new 122-0836 on by hand until the gasket contacts the base, and give it 3/4 to 1 full turn more by hand only. Do NOT use the filter wrench to tighten — overtightening damages the threads and can crack the filter housing.
Step 4: Add Fresh Oil
Remove the oil fill cap (top of generator) and insert a funnel. Pour in 1.8 quarts of SAE 15W-40 — slightly under the 2.0 quart maximum. Replace the cap. Wait 60 seconds for oil to settle into the sump and fill the new filter.
Step 5: Check Level & Test for Leaks
Pull the dipstick, wipe it clean, reinsert fully, then pull again. Oil should be at or slightly below the FULL mark — do not overfill. Start the generator and let it idle for 2 minutes. Watch the filter base and drain plug for any drips. If no leaks, shut down, recheck the dipstick, and top off if needed (the new filter absorbs about 3-4 ounces of oil on first fill). Reset the service reminder: press and hold the Stop button for 10 seconds until the Service light flashes 3 times.
Pro Tip: Dispose of used oil and the old filter at any auto parts store (AutoZone, O'Reilly, NAPA) — they accept it for free in most states.
Complete Onan QG Maintenance: All Three Filters
The 122-0836 oil filter is one part of a three-filter system on the Onan QG 5500/7000 generator. Cummins recommends replacing all three during the annual 150-hour service:
| Filter | Onan OEM | iFJF Part | Price | Interval |
|---|---|---|---|---|
| Oil Filter | 122-0836 | FJ-0836 | $16.99 | 150 hrs / annual |
| Air Filter | 140-3116 | 140-3116 | $22.99 | 150 hrs / annual |
| Fuel Pump | 149-2341-01 | 149-2341-01 | $45.99 | 300 hrs / 2 years |
| 💡 Tune-Up Kit | — | All 3 + Spark Plug | $85.99 | Best value (-15%) |
Buying the complete tune-up kit saves 15% versus individual filters and includes the spark plug. Everything ships from the same US warehouse.
FAQ
Will the 122-0836 fit a Cummins Onan QG 4000?
No. The QG 4000 (4KYFA-series) uses a smaller filter — Onan part number 122-0800. The 122-0836 is physically larger (3.6″ diameter vs 2.9″) and won't thread onto the QG 4000 mounting stud.
Is an aftermarket 122-0836 as reliable as OEM?
Aftermarket filters using SAE J1858-certified media (Baldwin B495, Fleetguard LF3335, Donaldson P502067) match or exceed OEM filtration efficiency. The key spec to check is the anti-drainback valve material — silicone valves (found in Fleetguard and Baldwin) last longer than the nitrile rubber used in budget alternatives. Budget eBay drop-shipped filters often fail the drainback test within 6 months.
How do I reset the maintenance reminder after changing the filter?
Onan QG generators with digital displays store service reminders: press and hold the "Stop" button for 10 seconds while the generator is OFF. The "Service" light will flash 3 times and clear. On older Marquis models without digital displays, there's no electronic reminder — log the hours in your RV maintenance notebook.
Can I use an automotive oil filter instead?
No — don't do this. Several online forums suggest using a Ford FL-820S or Motorcraft equivalent, but these filters lack the anti-drainback valve spec required for the Onan horizontal mounting position. The bypass pressure is also different (12 PSI for the FL-820S vs 18 PSI for the 122-0836), which means the automotive filter stays in bypass mode longer during cold starts, sending unfiltered oil to the generator bearings.
Does this filter come with a new O-ring?
Yes — every 122-0836 replacement includes a pre-lubricated nitrile O-ring in the box. Don't reuse the old O-ring even if it "looks fine" — heat cycling hardens the rubber over time, and a 50-cent O-ring failure dumps your entire oil charge onto the RV compartment floor in about 90 seconds.
What's the difference between 122-0836 and 0122-0836?
They're the same part. Cummins dropped the leading zero in their parts catalog circa 2010. The "0122-0836" prefix appears on older generator manuals (pre-2010 Marquis Gold); the "122-0836" format is current. Both numbers reference the identical filter — same dimensions, same thread pitch (3/4″-16 UNF), same bypass valve rating.
Why Buy from iFJF Direct?
🛒 122-0836 Oil Filter — $16.99, Ships from US Warehouse
The 122-0836 replacement filter fits every Onan QG 5500 and 7000 series generator from 2007 to current models. SAE J1858-certified filtration, silicone anti-drainback valve, and pre-lubricated O-ring included.
599 units in stock. Orders placed by 2 PM EST ship same day. RV owners who stock up for the season typically buy 2-3 at a time — the filter doesn't expire, and you'll need one every 150 hours regardless.
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