2020 BMW M340i – Rear Differential Fluid

This video shows you the correct way to change the rear differential fluid on a 2020+ BMW M340i (G20). BMW labels the diff fluid as a "lifetime fill," but on the B58-powered M340i — especially if you drive it hard or tow — fresh gear oil is cheap insurance against premature wear and that telltale rear-end whine or howl. We'll walk you through draining the old fluid, the correct fill level, and the right torque on the plugs. This service applies to: 2019–2024 BMW M340i / M340i xDrive (G20) (Also similar for other B58-equipped G20 3-Series and G22 4-Series rear diffs of the same era) Note: If your car is xDrive, it also has a separate front differential and transfer case that use their own fluids — those are NOT covered here. Also, if your M340i is equipped with the optional M Sport (electronically controlled limited-slip) differential, confirm the correct fluid spec before filling, as it may differ from the open-diff fluid. Parts & Specifications Component: Rear Differential (Final Drive) Gear Oil Recommended Fluid: BMW SAF-XO 75W-90, API GL-5 fully synthetic hypoid gear oil (BMW p/n 07 51 2 293 972), or an equivalent BMW-approved 75W-90 Fluid Capacity: approx. 0.9–1.0 liter (verify for your exact differential) Drain & Fill Plugs: 14mm Allen/hex head Torque Spec: approx. 60 Nm (44 lb-ft) for plugs with an O-ring / 65 Nm (48 lb-ft) for plugs with a sealing washer — verify which yours uses Pro Tip: Always crack the FILL plug loose first, before you drain. If the fill plug is seized and you've already drained the diff, you're stranded with no way to refill. Also, fill until fluid just begins to seep out of the fill hole with the car level — that's your correct level. Tools You Will Need: 14mm Allen/Hex Socket Ratchet and Torque Wrench Fluid Pump or Transfer Pump (to push gear oil into the fill hole) Drain Pan New Drain and Fill Plug Seals (crush washers or O-rings) Floor Jack and Jack Stands (or a lift) Shop Towels and Gloves Steps Covered: Prep & Safety: Lifting and leveling the car so the fill level reads correctly. Cracking the Fill Plug: Loosening the upper fill plug first to confirm it will come out. Draining: Removing the lower drain plug and letting the old fluid fully drain. Inspecting: Checking the old fluid and the magnetic drain plug for metal shavings. Sealing Surfaces: Installing fresh seals/washers on both plugs. Refilling: Pumping in BMW-approved 75W-90 until it seeps from the fill hole. Final Torque: Torquing the drain and fill plugs to spec. Cleanup & Check: Wiping down and checking for leaks after a short drive. Subscribe: / @TheMechanicOC Keywords: BMW M340i rear differential fluid, G20 diff fluid change, M340i gear oil, BMW SAF-XO 75W-90, B58 differential service, BMW lifetime fluid myth, DIY auto repair, TheMechanicOC, Mission Viejo BMW repair, how to change BMW differential fluid, M340i rear end whine, G20 3-series maintenance. DISCLAIMER: While TheMechanicOC strives to make the information provided in this video as accurate as possible, it makes no claims, promises, or guarantees about the accuracy, completeness or applicability of the content. All do-it-yourself projects entail risk. It is the sole responsibility of the viewer to assume this risk. TheMechanicOC is not liable for any loss, damage, or injury resulting from information posted in this video.