NHC MOTORS · SERVICE RECORD

BMW 520d GT: Oil Traces Around the Rear Differential Found During an Engine Oil Change

While changing the engine oil and filter on a 2016 BMW 520d GT, we found a wet area around the rear differential. It shows why the underside is worth checking at every oil change.

Draining the old engine oil on the lift.

2016 BMW 520d GT

Checking the underside during an engine oil change can turn up traces you would never notice in the parking lot. On this 520d GT, there was oil around the rear differential housing and the shaft connections.

We inspected this area while changing the engine oil and filter. In this case, we used the time spent draining and refilling the oil to check the condition of the rest of the car as well.

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We Changed the Engine Oil and Oil Filter

After checking the oil condition, we drained the old engine oil. We refilled with PETRONAS 5000AV 5W-30, fitted a MAHLE OX 404 D oil filter and added BG DOC.

At regular oil changes, we also check how much oil went in last time and how much was topped up in between. Comparing that with the amount drained shows whether the engine's oil consumption has changed.

Checking the engine oil condition before draining.

The MAHLE OX 404 D oil filter used for this change.

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The Area Around the Rear Differential Was Wet

We found oil traces on the rear differential housing and around the shaft connections. The engine and the differential use different oils. Oil on the underside does not automatically mean the engine is leaking.

Where oil shows up is not always where the leak starts. To decide what needs repairing, the surrounding area has to be checked and, if necessary, cleaned so we can see which spot gets wet again. If oil is dripping onto your parking space or the wet area is getting larger, have it inspected without delay.

Oil traces on the surface of the differential housing.

Close-up of the wet area around the axle shaft connection.

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We Also Checked the Belt Area and Tire Pressures

In the engine bay, we checked the belt and pulley area. We also set the tire pressures and topped up the washer fluid.

When you book an oil change, let us know about any noise you've been hearing or stains on your parking space. It helps us check those areas while the car is on the lift.

What We Checked During the Oil Change

Engine

Engine oil and oil filter service

Rear drivetrain

Checked traces on the differential housing and shaft connections

Engine bay

Inspected the belt and pulley area

Engine oil and rear differential oil are separate systems. For any oil traces, we find where the leak starts before deciding what to repair.

Frequently asked questions

If there is oil on the underside, does that mean the engine is leaking oil?

The first step is to identify which system the oil is coming from. On this car, the traces were around the rear differential housing and shaft connections, so we checked that location separately from the engine oil service.

Do oil traces around the differential need to be repaired right away?

Where the oil has collected may not be where the leak starts. We check the surrounding connections as well and, if necessary, clean the area to see whether the same spot gets wet again. If oil is dripping onto the ground or the wet area is spreading, please book an inspection of that area.

At Your Oil Change, Tell Us About Anything That Has Been Bothering You

At the oil change, we also inspect the underside and explain what needs attention now and what needs further checking. Please mention any stains where you park or new noises when you book.

We explain the work and estimate before proceeding with your consent.

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031-258-1617 · NHC Motors, Suwon · By appointment

Published 2026-09-26