Mercedes-Benz GLS-Class, X166 (USA / CAN)

Additional Notes

• Across all variants of the Mercedes-Benz GLS-Class X166 covered here, the front differential capacity is uniformly specified at 0.8 liter, regardless of whether the housing is standard or light alloy construction. Both housing types share the same fill volume for the front axle.
• The rear differential presents three distinct fixed capacity values — 0.95 liter, 1.1 liter, and 1.2 liter — listed as separate entries for each variant. These multiple values reflect the presence of different rear differential unit variants that may be fitted to the same model designation, each requiring a different fluid volume.
• Rear differentials with light alloy housings across all X166 variants carry a fill instruction rather than a fixed volume: fluid is added until it reaches the lower edge of the level plug opening. This method accounts for slight dimensional variation in cast alloy housings, where a fixed volume figure could result in overfilling or underfilling depending on the specific unit.
• The GLS 350d 4MATIC (166.823/824) and GLS 450 4MATIC (166.864) each appear in two separate model year groupings — 2015-2017 and 2017-2019 — with identical differential capacity figures across both periods. The year 2017 marks a specification boundary point for both variants, though the fluid volumes themselves remain unchanged between the two groupings.
• The GLS 550 4MATIC (166.873) specifications cover only the 2015-2017 period, while the GLS 63 AMG 4MATIC (166.875) spans 2015-2019 as a single continuous grouping without a mid-range split. The 63 AMG is the only variant in the dataset presented under a single uninterrupted year range.
• All differential fluid specifications across every variant and model year in the dataset are designated for normal use conditions. No severe-duty or alternative service interval figures appear for any of the front or rear differential positions listed.
• The 0.95 liter rear differential capacity represents the smallest of the three fixed rear fill volumes specified. At roughly 150 ml less than the 1.1 liter figure and 250 ml less than the 1.2 liter figure, the difference is meaningful in a service context where overfilling a differential can cause seal damage or fluid aeration under load.