Briggs and Stratton 84005958 Fuel Tank Cap

What It Is

The Briggs & Stratton 84005958 Fuel Tank Cap is a direct OEM replacement cap designed for select Briggs & Stratton lawn mower engines. It seals the fuel tank to prevent leaks and evaporation, and includes a built-in vent to equalize pressure during operation.

Fitment & Compatibility

Before buying, confirm your engine model number (found on the valve cover or blower housing). This cap fits specific Briggs & Stratton engines, primarily those on walk-behind mowers and some riding mowers from brands like Toro, Snapper, and Murray that use Briggs engines. It does not fit all Briggs engines—cross-reference with your existing cap’s part number or measure the cap diameter (approximately 1.5 inches) and thread pitch. This is an OEM part, not an aftermarket universal cap, so it matches the original fit exactly. Check that your tank neck is not cracked or warped, as a damaged neck won’t seal even with a new cap.

Key Things to Know

• Quality: OEM part, built to original specs—no fitment guesswork, and the vent mechanism is reliable.
• Installation: Trivial—unscrew old cap, screw on new one. No tools needed. Takes 30 seconds.
• Common gotcha: The vent can clog if debris or old gas residue is present. If the engine runs rough or stalls after the cap is tightened, the vent may be blocked—try loosening the cap slightly to test.
• Price note: At $36.40, it’s pricier than generic caps, but it’s the correct fit for many older Briggs engines where aftermarket caps often don’t seal or vent properly.

Should You Buy It

Buy this cap if you have a Briggs & Stratton engine with a damaged or missing fuel cap and you want a guaranteed, no-hassle seal. It’s ideal for owners of older walk-behind mowers (e.g., 1990s–2010s models) where aftermarket caps fail to match the venting or threading. Skip it if you can verify a cheaper universal cap works for your specific model—or if your tank neck is damaged, as a new cap won’t fix that.