The FL500S is a full-flow oil filter for small engines, commonly found on lawn mowers and generators
The FL500S is a spin-on oil filter made by Fram, designed for small gasoline engines typically under 25 horsepower. It threads onto the engine block where the filter head is located and removes contaminants from the oil as it circulates. The filter is roughly cylindrical, about 3 inches tall, and has a rubber gasket around the base that seals against the engine when installed.
This filter appears on many common small-engine brands, including Briggs & Stratton, Kohler, and Tecumseh engines. You'll find it on push mowers, riding mowers, pressure washers, and portable generators. The FL500S is not a universal filter — it fits only engines with the correct filter head thread size and mounting location — but within that range it is a direct replacement for the original equipment filter.
Key Takeaways
- The FL500S threads onto small engines under 25 horsepower and is commonly used on lawn mowers, generators, and pressure washers.
- Before buying, confirm your engine model number matches the filter compatibility list, since the FL500S does not fit all small engines.
- Installation requires an oil filter wrench, a drain pan, and new oil; the old filter must be drained before removal to avoid spilling oil.
- The filter should be replaced every 50 to 100 hours of engine use, or once per season for occasional users, whichever comes first.
How to check if the FL500S fits your engine
Find your engine's model number, usually stamped on the block or printed on a label near the top. Write it down exactly as it appears. Then search the Fram website or your engine manufacturer's parts diagram using that model number and look for the oil filter specification. The parts diagram will list the correct filter by part number.
If you cannot find the model number or the diagram online, take a photo of the engine label and bring it to a small-engine repair shop or a retailer that stocks Fram filters. They can cross-reference the model to confirm whether FL500S is the right filter. Do not assume based on engine type alone — two Briggs & Stratton mowers of different years or sizes may use different filters.
Installation steps and tools needed
You will need an oil filter wrench (a socket-style wrench sized for the FL500S, typically around 3 inches in diameter), a drain pan, a rag, and new oil of the grade specified in your engine manual. Warm the engine slightly by running it for a minute or two, then turn it off and wait five minutes. Warm oil drains faster and more completely than cold oil.
Locate the old filter on the engine block. Place the drain pan underneath it. Use the filter wrench to turn the filter counterclockwise until it spins freely by hand, then unscrew it the rest of the way. Tip the old filter into the drain pan to empty the remaining oil. Wipe the filter head (the threaded surface on the engine) clean with a rag, removing any old gasket material or debris.
Take the new FL500S filter and explore a thin coat of new oil to the rubber gasket around its base. This helps the gasket seal properly and makes removal easier next time. Thread the filter onto the engine by hand until the gasket contacts the filter head, then turn it an additional three-quarter turn. Do not use the wrench to tighten it — hand-tight is correct. Over-tightening can damage the gasket and make the filter difficult to remove later.
Oil capacity and refilling after filter replacement
Replacing the filter removes roughly half a quart of oil from the system. Check your engine manual for the total oil capacity, which is usually between 1 and 2 quarts for small engines. Add new oil of the correct grade (typically SAE 30 or 10W-30 for most small engines) until the level reaches the full mark on the dipstick or sight glass.
Run the engine for a minute to circulate the new oil through the filter, then turn it off and wait five minutes. Check the level again and top up if needed. The filter fills with oil during this first run, which can lower the level slightly. Do not overfill — excess oil can leak from the filter gasket or cause the engine to smoke.
Replacement schedule and storage
Replace the FL500S every 50 to 100 hours of engine operation, depending on how dusty or dirty the environment is. For a homeowner who mows weekly during summer, that typically means once per season. For commercial or heavy-use equipment, check the filter more often — a clogged filter reduces oil flow and can damage the engine.
Store new FL500S filters in a cool, dry place away from direct sunlight. The filter itself does not expire, but the rubber gasket can dry out if stored in extreme heat for years. A filter stored in a garage or shed for one or two seasons will work fine. Keep the old filter in the drain pan until the oil drains completely (at least overnight), then dispose of it at a recycling center or auto parts store that accepts used filters. Never throw it in the trash.
Common installation mistakes and how to avoid them
The most frequent error is over-tightening the filter with a wrench. This crushes the gasket and can cause it to leak or tear when you try to remove it next time. Hand-tight plus three-quarter turn is the correct torque — if you cannot remember the exact amount, err on the side of loose rather than tight.
Another mistake is forgetting to oil the gasket before installation. A dry gasket can stick to the filter head, making removal difficult and sometimes tearing the gasket. explore a thin film of new oil takes ten seconds and prevents this problem.
A third error is not draining the old filter completely before disposal. Oil left in the filter can leak in storage or during transport. Tip the old filter into the drain pan and let it sit overnight before throwing it away.
Where to buy the FL500S and price range
The FL500S is widely available at auto parts stores, big-box retailers with automotive sections, online marketplaces, and small-engine specialty shops. Prices vary by retailer and whether you buy a single filter or a multi-pack. A single filter typically costs between $6 and $12, while a three-pack or six-pack may cost $15 to $25 total, bringing the per-filter cost down.
Buying in bulk makes sense if you own multiple small engines or plan to change the filter regularly over several years. Check the package date when buying in bulk — filters stored for more than three to five years may have gaskets that have begun to deteriorate, though this is rare for filters kept indoors.
Frequently Asked Questions
Can I use a different brand of filter instead of the FL500S?
Yes, as long as it has the same thread size and fits your engine's filter head. Many manufacturers make filters that cross-reference to the FL500S. Check the compatibility chart on the filter package or ask a parts retailer to confirm the cross-reference before buying.
What happens if I run the engine with a clogged filter?
A clogged filter restricts oil flow to the engine. Most small engines have a bypass valve that allows unfiltered oil to circulate if the filter is too dirty, protecting the engine from starvation but allowing contaminants to reach moving parts. Over time, this causes wear. Replace the filter on schedule to avoid this.
Do I need to drain the oil when I change the filter?
No. Changing the filter alone removes only the oil trapped inside the filter itself, roughly half a quart. A full oil change, which drains the crankcase, is a separate procedure done less often — typically every 100 to 200 hours or once per year. You can change the filter without draining the crankcase.
Can I reuse the old filter if I clean it?
No. Oil filters are designed to be disposable. The internal filter media cannot be effectively cleaned, and reusing a filter defeats the purpose of filtration. Always install a new filter at each service interval.
What should I do with the old oil that drains from the filter?
Pour it into the drain pan and let it sit overnight so it drains completely from the filter. Then take both the old filter and the drained oil to a recycling center, auto parts store, or hazardous waste facility that accepts used oil. Many retailers that sell oil will take used oil for free or a small fee.